diff --git a/Changes.md b/Changes.md
index 8c724204ff..310d9fd0e8 100644
--- a/Changes.md
+++ b/Changes.md
@@ -5,6 +5,9 @@ Unreleased
   ([#1040](https://github.com/melange-re/melange/pull/1040))
 - runtime: add some bindings to `Js.Bigint`
   ([#1044](https://github.com/melange-re/melange/pull/1044))
+- core: emit `throw new Error(..)` rather than throwing a JS object with the
+  Melange exception payload
+  ([#1036](https://github.com/melange-re/melange/pull/1036))
 
 3.0.0 2024-01-28
 ---------------
diff --git a/jscomp/core/j.mli b/jscomp/core/j.mli
index 7acfb5680a..9274429f7b 100644
--- a/jscomp/core/j.mli
+++ b/jscomp/core/j.mli
@@ -142,7 +142,7 @@ and expression_desc =
   (* A string is UTF-8 encoded, the string may contain
      escape sequences.
      The first argument is used to mark it is non-pure, please
-     don't optimize it, since it does have side effec,
+     don't optimize it, since it does have side effects,
      examples like "use asm;" and our compiler may generate "error;..."
      which is better to leave it alone
      The last argument is passed from as `j` from `{j||j}`
diff --git a/jscomp/core/js_dump.ml b/jscomp/core/js_dump.ml
index 58153629eb..db263d0602 100644
--- a/jscomp/core/js_dump.ml
+++ b/jscomp/core/js_dump.ml
@@ -130,8 +130,11 @@ let throw_indent = String.length L.throw / Js_pp.indent_length
 let semi cxt = string cxt L.semi
 let comma cxt = string cxt L.comma
 
+let new_error name cause =
+  E.new_ (E.js_global Js_dump_lit.error) [ name; cause ]
+
 let exn_block_as_obj ~(stack : bool) (el : J.expression list) (ext : J.tag_info)
-    : J.expression_desc =
+    : J.expression =
   let field_name =
     match ext with
     | Blk_extension -> (
@@ -140,11 +143,32 @@ let exn_block_as_obj ~(stack : bool) (el : J.expression list) (ext : J.tag_info)
         fun i -> match i with 0 -> L.exception_id | i -> ss.(i - 1))
     | _ -> assert false
   in
-  Object
-    (if stack then
-       List.mapi ~f:(fun i e -> (Js_op.Lit (field_name i), e)) el
-       @ [ (Js_op.Lit "Error", E.new_ (E.js_global "Error") []) ]
-     else List.mapi ~f:(fun i e -> (Js_op.Lit (field_name i), e)) el)
+  let cause =
+    {
+      J.expression_desc =
+        Object (List.mapi ~f:(fun i e -> (Js_op.Lit (field_name i), e)) el);
+      comment = None;
+      loc = None;
+    }
+  in
+  if stack then
+    new_error (List.hd el)
+      {
+        J.expression_desc = Object [ (Lit Js_dump_lit.cause, cause) ];
+        comment = None;
+        loc = None;
+      }
+  else cause
+
+let exn_ref_as_obj e : J.expression =
+  let cause = { J.expression_desc = e; comment = None; loc = None } in
+  new_error
+    (E.record_access cause Js_dump_lit.exception_id 0l)
+    {
+      J.expression_desc = Object [ (Lit Js_dump_lit.cause, cause) ];
+      comment = None;
+      loc = None;
+    }
 
 let rec iter_lst cxt ls element inter =
   match ls with
@@ -785,7 +809,7 @@ and expression_desc cxt ~(level : int) x : cxt =
                ])
       | _ -> assert false)
   | Caml_block (el, _, _, ((Blk_extension | Blk_record_ext _) as ext)) ->
-      expression_desc cxt ~level (exn_block_as_obj ~stack:false el ext)
+      expression cxt ~level (exn_block_as_obj ~stack:false el ext)
   | Caml_block (el, _, tag, Blk_record_inlined p) ->
       let objs =
         let tails =
@@ -809,9 +833,7 @@ and expression_desc cxt ~(level : int) x : cxt =
         let tails =
           List.mapi
             ~f:(fun i e ->
-              ( Js_op.Lit
-                  (Js_exp_make.variant_pos ~constr:p.name (Int32.of_int i)),
-                e ))
+              (Js_op.Lit (E.variant_pos ~constr:p.name (Int32.of_int i)), e))
             el
           @
           if !Js_config.debug && not_is_cons then
@@ -1218,8 +1240,13 @@ and statement_desc top cxt (s : J.statement_desc) : cxt =
       let e =
         match e.expression_desc with
         | Caml_block (el, _, _, ((Blk_extension | Blk_record_ext _) as ext)) ->
-            { e with expression_desc = exn_block_as_obj ~stack:true el ext }
-        | _ -> e
+            {
+              e with
+              expression_desc =
+                (exn_block_as_obj ~stack:true el ext).expression_desc;
+            }
+        | exp ->
+            { e with expression_desc = (exn_ref_as_obj exp).expression_desc }
       in
       string cxt L.throw;
       space cxt;
diff --git a/jscomp/core/js_dump_lit.ml b/jscomp/core/js_dump_lit.ml
index e9685ada57..85ea269e3e 100644
--- a/jscomp/core/js_dump_lit.ml
+++ b/jscomp/core/js_dump_lit.ml
@@ -80,6 +80,8 @@ let minus_minus = "--"
 (** debug symbols *)
 
 let case = "case"
+let cause = "cause"
+let error = "Error"
 let exception_id = "MEL_EXN_ID"
 let polyvar_hash = "NAME"
 let polyvar_value = "VAL"
diff --git a/jscomp/core/js_exp_make.ml b/jscomp/core/js_exp_make.ml
index cd8ca59c39..358051b26b 100644
--- a/jscomp/core/js_exp_make.ml
+++ b/jscomp/core/js_exp_make.ml
@@ -350,7 +350,7 @@ let poly_var_value_access (e : t) =
       match l with _ :: v :: _ -> v | _ -> assert false)
   | _ -> make_expression (Static_index (e, Js_dump_lit.polyvar_value, Some 1l))
 
-let extension_access (e : t) name (pos : int32) : t =
+let extension_access (e : t) ?name (pos : int32) : t =
   match e.expression_desc with
   | Array (l, _) (* Float i -- should not appear here *)
   | Caml_block (l, _, _, _)
diff --git a/jscomp/core/js_exp_make.mli b/jscomp/core/js_exp_make.mli
index 31611b725c..9d903bf6ef 100644
--- a/jscomp/core/js_exp_make.mli
+++ b/jscomp/core/js_exp_make.mli
@@ -155,7 +155,7 @@ val inline_record_access : t -> string -> Int32.t -> t
 val variant_pos : constr:string -> int32 -> string
 val variant_access : t -> int32 -> t
 val cons_access : t -> int32 -> t
-val extension_access : t -> string option -> Int32.t -> t
+val extension_access : t -> ?name:string -> Int32.t -> t
 val record_assign : t -> int32 -> string -> t -> t
 val poly_var_tag_access : t -> t
 val poly_var_value_access : t -> t
diff --git a/jscomp/core/js_of_lam_block.ml b/jscomp/core/js_of_lam_block.ml
index b04730a4a5..e03dcc8c60 100644
--- a/jscomp/core/js_of_lam_block.ml
+++ b/jscomp/core/js_of_lam_block.ml
@@ -48,8 +48,8 @@ let field (field_info : Lam_compat.field_dbg_info) e (i : int32) =
         e i
   | Fld_poly_var_content -> E.poly_var_value_access e
   | Fld_poly_var_tag -> E.poly_var_tag_access e
-  | Fld_record_extension { name } -> E.extension_access e (Some name) i
-  | Fld_extension -> E.extension_access e None i
+  | Fld_record_extension { name } -> E.extension_access e ~name i
+  | Fld_extension -> E.extension_access e i
   | Fld_variant -> E.variant_access e i
   | Fld_cons -> E.cons_access e i
   | Fld_record_inline { name } -> E.inline_record_access e name i
diff --git a/jscomp/core/lam_convert.cppo.ml b/jscomp/core/lam_convert.cppo.ml
index d8aed3d2df..6d84d43ce2 100644
--- a/jscomp/core/lam_convert.cppo.ml
+++ b/jscomp/core/lam_convert.cppo.ml
@@ -24,14 +24,17 @@
 
 open Import
 
-let caml_id_field_info : Lambda.field_dbg_info =
-  Fld_record { name = Js_dump_lit.exception_id; mutable_flag = Immutable }
-
-let lam_caml_id : Lam_primitive.t = Pfield (0, caml_id_field_info)
 let prim = Lam.prim
 
-let lam_extension_id loc (head : Lam.t) =
-  prim ~primitive:lam_caml_id ~args:[ head ] loc
+let lam_extension_id =
+  let lam_caml_id : Lam_primitive.t =
+    let caml_id_field_info : Lambda.field_dbg_info =
+      Fld_record { name = Js_dump_lit.exception_id; mutable_flag = Immutable }
+    in
+    Pfield (0, caml_id_field_info)
+  in
+  fun loc (head : Lam.t) ->
+    prim ~primitive:lam_caml_id ~args:[ head ] loc
 
 let lazy_block_info : Lam.Tag_info.t =
   let lazy_done = "LAZY_DONE" and lazy_val = "VAL" in
diff --git a/jscomp/runtime/caml_format.ml b/jscomp/runtime/caml_format.ml
index 6d902535b9..f709e25eb9 100644
--- a/jscomp/runtime/caml_format.ml
+++ b/jscomp/runtime/caml_format.ml
@@ -616,7 +616,7 @@ let float_of_string : string -> exn -> float =
         return Infinity;
     if (/^-inf(inity)?$/i.test(s))
         return -Infinity;
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, { cause: exn });
 }
 |}]
 
diff --git a/jscomp/runtime/caml_js_exceptions.ml b/jscomp/runtime/caml_js_exceptions.ml
index e46ea78452..3693e336b1 100644
--- a/jscomp/runtime/caml_js_exceptions.ml
+++ b/jscomp/runtime/caml_js_exceptions.ml
@@ -1,6 +1,7 @@
 open Melange_mini_stdlib
 
 type t = Any : 'a -> t [@@unboxed]
+type js_error = { cause : exn }
 
 exception Error of t
 
@@ -9,7 +10,10 @@ exception Error of t
    [Error] is defined here
 *)
 let internalToOCamlException (e : Obj.t) =
-  if Caml_exceptions.caml_is_extension e then (Obj.magic e : exn)
+  if
+    (not (Js_internal.testAny e))
+    && Caml_exceptions.caml_is_extension (Obj.magic e : js_error).cause
+  then (Obj.magic e : js_error).cause
   else Error (Any e)
 
 let caml_as_js_exn exn = match exn with Error t -> Some t | _ -> None
diff --git a/jscomp/runtime/caml_lexer.ml b/jscomp/runtime/caml_lexer.ml
index 949223b834..06000d6428 100644
--- a/jscomp/runtime/caml_lexer.ml
+++ b/jscomp/runtime/caml_lexer.ml
@@ -159,7 +159,7 @@ let caml_lex_engine_aux : lex_tables -> int -> lexbuf -> exn -> int =
         if (state < 0) {
             lexbuf.lex_curr_pos = lexbuf.lex_last_pos;
             if (lexbuf.lex_last_action == -1)
-                throw exn
+              throw new Error(exn.MEL_EXN_ID, { cause: exn })
             else
                 return lexbuf.lex_last_action;
         }
@@ -305,7 +305,7 @@ let caml_new_lex_engine_aux : lex_tables -> int -> lexbuf -> exn -> int =
         if (state < 0) {
             lexbuf.lex_curr_pos = lexbuf.lex_last_pos;
             if (lexbuf.lex_last_action == -1)
-                throw exn;
+                throw new Error(exn.MEL_EXN_ID, { cause: exn })
             else
                 return lexbuf.lex_last_action;
         }
diff --git a/jscomp/test/dist/jscomp/test/406_primitive_test.js b/jscomp/test/dist/jscomp/test/406_primitive_test.js
index 6a78c9e7c5..33075caabe 100644
--- a/jscomp/test/dist/jscomp/test/406_primitive_test.js
+++ b/jscomp/test/dist/jscomp/test/406_primitive_test.js
@@ -32,11 +32,12 @@ function f(param) {
   try {
     for(var i = 0; i <= 200; ++i){
       if (i === 10) {
-        throw {
-              MEL_EXN_ID: A,
-              _1: 0,
-              Error: new Error()
-            };
+        throw new Error(A, {
+                  cause: {
+                    MEL_EXN_ID: A,
+                    _1: 0
+                  }
+                });
       }
       
     }
@@ -47,7 +48,9 @@ function f(param) {
     if (exn.MEL_EXN_ID === A) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/adt_optimize_test.js b/jscomp/test/dist/jscomp/test/adt_optimize_test.js
index 1bd3635451..50c11f1c70 100644
--- a/jscomp/test/dist/jscomp/test/adt_optimize_test.js
+++ b/jscomp/test/dist/jscomp/test/adt_optimize_test.js
@@ -159,15 +159,16 @@ function f11(x) {
   if (x.TAG === /* D */0) {
     return 1;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/adt_optimize_test.ml",
-          191,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/adt_optimize_test.ml",
+                191,
+                9
+              ]
+            }
+          });
 }
 
 exports.f = f;
diff --git a/jscomp/test/dist/jscomp/test/app_root_finder.js b/jscomp/test/dist/jscomp/test/app_root_finder.js
index e2a8a25b9e..9f2d475f47 100644
--- a/jscomp/test/dist/jscomp/test/app_root_finder.js
+++ b/jscomp/test/dist/jscomp/test/app_root_finder.js
@@ -15,10 +15,11 @@ function find_package_json(_dir) {
     }
     var new_dir = Path.dirname(dir);
     if (new_dir === dir) {
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
     _dir = new_dir;
     continue ;
diff --git a/jscomp/test/dist/jscomp/test/argv_test.js b/jscomp/test/dist/jscomp/test/argv_test.js
index 5760d8453c..b7a4223d47 100644
--- a/jscomp/test/dist/jscomp/test/argv_test.js
+++ b/jscomp/test/dist/jscomp/test/argv_test.js
@@ -50,27 +50,29 @@ Stdlib__Arg.parse_argv(undefined, [
     ], arg_spec, anno_fun, usage_msg);
 
 if (compile.contents !== true) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/argv_test.ml",
-          20,
-          0
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/argv_test.ml",
+                20,
+                0
+              ]
+            }
+          });
 }
 
 if (test.contents !== false) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/argv_test.ml",
-          21,
-          0
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/argv_test.ml",
+                21,
+                0
+              ]
+            }
+          });
 }
 
 exports.anno_fun = anno_fun;
diff --git a/jscomp/test/dist/jscomp/test/arith_parser.js b/jscomp/test/dist/jscomp/test/arith_parser.js
index 3b78ada359..7ac52de29f 100644
--- a/jscomp/test/dist/jscomp/test/arith_parser.js
+++ b/jscomp/test/dist/jscomp/test/arith_parser.js
@@ -45,11 +45,12 @@ var yynames_block = "NUMERAL\0IDENT\0";
 
 var yyact = [
   (function (param) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "parser",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "parser"
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -115,11 +116,12 @@ var yyact = [
       return Stdlib__Parsing.peek_val(__caml_parser_env, 1);
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     })
 ];
 
diff --git a/jscomp/test/dist/jscomp/test/arity_infer.js b/jscomp/test/dist/jscomp/test/arity_infer.js
index 42a29a1d51..b516d29a54 100644
--- a/jscomp/test/dist/jscomp/test/arity_infer.js
+++ b/jscomp/test/dist/jscomp/test/arity_infer.js
@@ -11,19 +11,21 @@ function f0(x) {
         return x + 1 | 0;
       });
   } else {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   return tmp(3);
 }
 
 function f1(x) {
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
   return Curry._1(undefined, x);
 }
 
@@ -51,10 +53,11 @@ function f3(x) {
           });
         break;
     default:
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
   }
   return tmp(3);
 }
diff --git a/jscomp/test/dist/jscomp/test/array_safe_get.js b/jscomp/test/dist/jscomp/test/array_safe_get.js
index e54806b761..1be243b74d 100644
--- a/jscomp/test/dist/jscomp/test/array_safe_get.js
+++ b/jscomp/test/dist/jscomp/test/array_safe_get.js
@@ -21,7 +21,9 @@ catch (raw_exn){
     console.log(exn._1);
     y = 0;
   } else {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/array_test.js b/jscomp/test/dist/jscomp/test/array_test.js
index 8f39b41094..e23d859f10 100644
--- a/jscomp/test/dist/jscomp/test/array_test.js
+++ b/jscomp/test/dist/jscomp/test/array_test.js
@@ -21,10 +21,11 @@ function starts_with(xs, prefix, p) {
   try {
     for(var i = 0; i < len2; ++i){
       if (!Curry._2(p, Caml_array.get(xs, i), Caml_array.get(prefix, i))) {
-        throw {
-              MEL_EXN_ID: H,
-              Error: new Error()
-            };
+        throw new Error(H, {
+                  cause: {
+                    MEL_EXN_ID: H
+                  }
+                });
       }
       
     }
@@ -35,7 +36,9 @@ function starts_with(xs, prefix, p) {
     if (exn.MEL_EXN_ID === H) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/ast_abstract_test.js b/jscomp/test/dist/jscomp/test/ast_abstract_test.js
index 4276a61e24..9677aee644 100644
--- a/jscomp/test/dist/jscomp/test/ast_abstract_test.js
+++ b/jscomp/test/dist/jscomp/test/ast_abstract_test.js
@@ -111,15 +111,16 @@ function bToJs(param) {
 
 function bFromJs(param) {
   if (!(param <= 3 && 0 <= param)) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "_none_",
-            0,
-            -1
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "_none_",
+                  0,
+                  -1
+                ]
+              }
+            });
   }
   return param - 0 | 0;
 }
@@ -142,15 +143,16 @@ function cToJs(param) {
 
 function cFromJs(param) {
   if (!(param <= 6 && 3 <= param)) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "_none_",
-            0,
-            -1
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "_none_",
+                  0,
+                  -1
+                ]
+              }
+            });
   }
   return param - 3 | 0;
 }
@@ -173,15 +175,16 @@ function hToJs(param) {
 
 function hFromJs(param) {
   if (!(param <= 1 && 0 <= param)) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "_none_",
-            0,
-            -1
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "_none_",
+                  0,
+                  -1
+                ]
+              }
+            });
   }
   return param - 0 | 0;
 }
diff --git a/jscomp/test/dist/jscomp/test/ast_mapper_defensive_test.js b/jscomp/test/dist/jscomp/test/ast_mapper_defensive_test.js
index 74c0364d57..2358b75ea3 100644
--- a/jscomp/test/dist/jscomp/test/ast_mapper_defensive_test.js
+++ b/jscomp/test/dist/jscomp/test/ast_mapper_defensive_test.js
@@ -34,15 +34,16 @@ function aToJs(param) {
 
 function aFromJs(param) {
   if (!(param <= 2 && 0 <= param)) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "_none_",
-            0,
-            -1
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "_none_",
+                  0,
+                  -1
+                ]
+              }
+            });
   }
   return param - 0 | 0;
 }
diff --git a/jscomp/test/dist/jscomp/test/bb.js b/jscomp/test/dist/jscomp/test/bb.js
index b03e5bc94f..2b35bc51e6 100644
--- a/jscomp/test/dist/jscomp/test/bb.js
+++ b/jscomp/test/dist/jscomp/test/bb.js
@@ -21,15 +21,16 @@ function ff(x) {
     case "c" :
         return "c";
     default:
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bb.ml",
-              17,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bb.ml",
+                    17,
+                    9
+                  ]
+                }
+              });
   }
 }
 
@@ -46,15 +47,16 @@ function test(x) {
         match = "c";
         break;
     default:
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bb.ml",
-              26,
-              13
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bb.ml",
+                    26,
+                    13
+                  ]
+                }
+              });
   }
   if (match === "b") {
     return "b";
diff --git a/jscomp/test/dist/jscomp/test/bdd.js b/jscomp/test/dist/jscomp/test/bdd.js
index c83c9f4f8b..dd4c277a7a 100644
--- a/jscomp/test/dist/jscomp/test/bdd.js
+++ b/jscomp/test/dist/jscomp/test/bdd.js
@@ -66,15 +66,16 @@ function resize(newSize) {
       }
       var n = bucket.hd;
       if (typeof n === "number") {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/bdd.ml",
-                54,
-                27
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/bdd.ml",
+                      54,
+                      27
+                    ]
+                  }
+                });
       }
       var ind = hashVal(getId(n._0), getId(n._3), n._1) & newSz_1;
       Caml_array.set(newArr, ind, {
@@ -130,15 +131,16 @@ function mkNode(low, v, high) {
     if (b) {
       var n = b.hd;
       if (typeof n === "number") {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/bdd.ml",
-                99,
-                31
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/bdd.ml",
+                      99,
+                      31
+                    ]
+                  }
+                });
       }
       if (v === n._1 && idl === getId(n._0) && idh === getId(n._3)) {
         return n;
@@ -374,15 +376,16 @@ function main(param) {
   if (succeeded) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bdd.ml",
-          233,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bdd.ml",
+                233,
+                2
+              ]
+            }
+          });
 }
 
 main(undefined);
diff --git a/jscomp/test/dist/jscomp/test/bench.js b/jscomp/test/dist/jscomp/test/bench.js
index 330a1f1741..3867376f5a 100644
--- a/jscomp/test/dist/jscomp/test/bench.js
+++ b/jscomp/test/dist/jscomp/test/bench.js
@@ -24,11 +24,12 @@ function init(l, f) {
     return [];
   }
   if (l < 0) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Array.init",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Array.init"
+              }
+            });
   }
   var res = Caml_array.make(l, f$1(0));
   for(var i = 1; i < l; ++i){
diff --git a/jscomp/test/dist/jscomp/test/big_polyvar_test.js b/jscomp/test/dist/jscomp/test/big_polyvar_test.js
index e46ea9e679..ec4d83e079 100644
--- a/jscomp/test/dist/jscomp/test/big_polyvar_test.js
+++ b/jscomp/test/dist/jscomp/test/big_polyvar_test.js
@@ -25,3615 +25,3916 @@ function eq(x, y) {
 }
 
 if (!eq(tFromJs("variant0"), "variant0")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          610,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                610,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant1"), "variant1")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          611,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                611,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant2"), "variant2")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          612,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                612,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant3"), "variant3")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          613,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                613,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant4"), "variant4")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          614,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                614,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant5"), "variant5")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          615,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                615,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant6"), "variant6")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          616,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                616,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant7"), "variant7")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          617,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                617,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant8"), "variant8")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          618,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                618,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant9"), "variant9")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          619,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                619,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant10"), "variant10")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          620,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                620,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant11"), "variant11")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          621,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                621,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant12"), "variant12")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          622,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                622,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant13"), "variant13")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          623,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                623,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant14"), "variant14")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          624,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                624,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant15"), "variant15")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          625,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                625,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant16"), "variant16")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          626,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                626,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant17"), "variant17")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          627,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                627,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant18"), "variant18")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          628,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                628,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant19"), "variant19")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          629,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                629,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant20"), "variant20")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          630,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                630,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant21"), "variant21")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          631,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                631,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant22"), "variant22")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          632,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                632,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant23"), "variant23")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          633,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                633,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant24"), "variant24")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          634,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                634,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant25"), "variant25")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          635,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                635,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant26"), "variant26")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          636,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                636,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant27"), "variant27")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          637,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                637,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant28"), "variant28")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          638,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                638,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant29"), "variant29")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          639,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                639,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant30"), "variant30")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          640,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                640,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant31"), "variant31")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          641,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                641,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant32"), "variant32")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          642,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                642,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant33"), "variant33")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          643,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                643,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant34"), "variant34")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          644,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                644,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant35"), "variant35")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          645,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                645,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant36"), "variant36")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          646,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                646,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant37"), "variant37")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          647,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                647,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant38"), "variant38")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          648,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                648,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant39"), "variant39")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          649,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                649,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant40"), "variant40")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          650,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                650,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant41"), "variant41")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          651,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                651,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant42"), "variant42")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          652,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                652,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant43"), "variant43")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          653,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                653,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant44"), "variant44")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          654,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                654,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant45"), "variant45")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          655,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                655,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant46"), "variant46")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          656,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                656,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant47"), "variant47")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          657,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                657,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant48"), "variant48")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          658,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                658,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant49"), "variant49")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          659,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                659,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant50"), "variant50")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          660,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                660,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant51"), "variant51")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          661,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                661,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant52"), "variant52")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          662,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                662,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant53"), "variant53")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          663,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                663,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant54"), "variant54")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          664,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                664,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant55"), "variant55")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          665,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                665,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant56"), "variant56")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          666,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                666,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant57"), "variant57")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          667,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                667,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant58"), "variant58")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          668,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                668,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant59"), "variant59")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          669,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                669,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant60"), "variant60")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          670,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                670,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant61"), "variant61")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          671,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                671,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant62"), "variant62")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          672,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                672,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant63"), "variant63")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          673,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                673,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant64"), "variant64")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          674,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                674,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant65"), "variant65")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          675,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                675,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant66"), "variant66")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          676,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                676,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant67"), "variant67")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          677,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                677,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant68"), "variant68")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          678,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                678,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant69"), "variant69")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          679,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                679,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant70"), "variant70")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          680,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                680,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant71"), "variant71")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          681,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                681,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant72"), "variant72")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          682,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                682,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant73"), "variant73")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          683,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                683,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant74"), "variant74")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          684,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                684,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant75"), "variant75")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          685,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                685,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant76"), "variant76")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          686,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                686,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant77"), "variant77")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          687,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                687,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant78"), "variant78")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          688,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                688,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant79"), "variant79")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          689,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                689,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant80"), "variant80")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          690,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                690,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant81"), "variant81")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          691,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                691,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant82"), "variant82")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          692,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                692,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant83"), "variant83")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          693,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                693,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant84"), "variant84")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          694,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                694,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant85"), "variant85")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          695,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                695,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant86"), "variant86")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          696,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                696,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant87"), "variant87")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          697,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                697,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant88"), "variant88")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          698,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                698,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant89"), "variant89")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          699,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                699,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant90"), "variant90")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          700,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                700,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant91"), "variant91")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          701,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                701,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant92"), "variant92")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          702,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                702,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant93"), "variant93")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          703,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                703,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant94"), "variant94")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          704,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                704,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant95"), "variant95")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          705,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                705,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant96"), "variant96")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          706,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                706,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant97"), "variant97")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          707,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                707,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant98"), "variant98")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          708,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                708,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant99"), "variant99")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          709,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                709,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant100"), "variant100")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          710,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                710,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant101"), "variant101")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          711,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                711,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant102"), "variant102")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          712,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                712,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant103"), "variant103")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          713,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                713,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant104"), "variant104")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          714,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                714,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant105"), "variant105")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          715,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                715,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant106"), "variant106")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          716,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                716,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant107"), "variant107")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          717,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                717,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant108"), "variant108")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          718,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                718,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant109"), "variant109")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          719,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                719,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant110"), "variant110")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          720,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                720,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant111"), "variant111")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          721,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                721,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant112"), "variant112")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          722,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                722,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant113"), "variant113")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          723,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                723,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant114"), "variant114")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          724,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                724,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant115"), "variant115")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          725,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                725,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant116"), "variant116")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          726,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                726,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant117"), "variant117")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          727,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                727,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant118"), "variant118")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          728,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                728,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant119"), "variant119")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          729,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                729,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant120"), "variant120")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          730,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                730,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant121"), "variant121")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          731,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                731,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant122"), "variant122")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          732,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                732,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant123"), "variant123")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          733,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                733,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant124"), "variant124")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          734,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                734,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant125"), "variant125")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          735,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                735,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant126"), "variant126")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          736,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                736,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant127"), "variant127")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          737,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                737,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant128"), "variant128")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          738,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                738,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant129"), "variant129")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          739,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                739,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant130"), "variant130")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          740,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                740,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant131"), "variant131")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          741,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                741,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant132"), "variant132")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          742,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                742,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant133"), "variant133")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          743,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                743,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant134"), "variant134")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          744,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                744,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant135"), "variant135")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          745,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                745,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant136"), "variant136")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          746,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                746,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant137"), "variant137")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          747,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                747,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant138"), "variant138")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          748,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                748,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant139"), "variant139")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          749,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                749,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant140"), "variant140")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          750,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                750,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant141"), "variant141")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          751,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                751,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant142"), "variant142")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          752,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                752,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant143"), "variant143")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          753,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                753,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant144"), "variant144")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          754,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                754,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant145"), "variant145")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          755,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                755,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant146"), "variant146")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          756,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                756,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant147"), "variant147")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          757,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                757,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant148"), "variant148")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          758,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                758,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant149"), "variant149")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          759,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                759,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant150"), "variant150")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          760,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                760,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant151"), "variant151")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          761,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                761,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant152"), "variant152")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          762,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                762,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant153"), "variant153")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          763,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                763,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant154"), "variant154")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          764,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                764,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant155"), "variant155")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          765,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                765,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant156"), "variant156")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          766,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                766,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant157"), "variant157")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          767,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                767,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant158"), "variant158")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          768,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                768,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant159"), "variant159")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          769,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                769,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant160"), "variant160")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          770,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                770,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant161"), "variant161")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          771,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                771,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant162"), "variant162")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          772,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                772,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant163"), "variant163")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          773,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                773,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant164"), "variant164")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          774,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                774,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant165"), "variant165")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          775,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                775,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant166"), "variant166")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          776,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                776,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant167"), "variant167")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          777,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                777,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant168"), "variant168")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          778,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                778,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant169"), "variant169")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          779,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                779,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant170"), "variant170")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          780,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                780,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant171"), "variant171")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          781,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                781,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant172"), "variant172")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          782,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                782,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant173"), "variant173")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          783,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                783,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant174"), "variant174")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          784,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                784,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant175"), "variant175")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          785,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                785,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant176"), "variant176")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          786,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                786,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant177"), "variant177")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          787,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                787,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant178"), "variant178")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          788,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                788,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant179"), "variant179")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          789,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                789,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant180"), "variant180")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          790,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                790,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant181"), "variant181")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          791,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                791,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant182"), "variant182")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          792,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                792,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant183"), "variant183")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          793,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                793,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant184"), "variant184")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          794,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                794,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant185"), "variant185")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          795,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                795,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant186"), "variant186")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          796,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                796,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant187"), "variant187")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          797,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                797,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant188"), "variant188")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          798,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                798,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant189"), "variant189")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          799,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                799,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant190"), "variant190")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          800,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                800,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant191"), "variant191")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          801,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                801,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant192"), "variant192")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          802,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                802,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant193"), "variant193")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          803,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                803,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant194"), "variant194")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          804,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                804,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant195"), "variant195")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          805,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                805,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant196"), "variant196")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          806,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                806,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant197"), "variant197")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          807,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                807,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant198"), "variant198")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          808,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                808,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant199"), "variant199")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          809,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                809,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant200"), "variant200")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          810,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                810,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant201"), "variant201")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          811,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                811,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant202"), "variant202")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          812,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                812,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant203"), "variant203")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          813,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                813,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant204"), "variant204")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          814,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                814,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant205"), "variant205")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          815,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                815,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant206"), "variant206")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          816,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                816,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant207"), "variant207")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          817,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                817,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant208"), "variant208")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          818,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                818,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant209"), "variant209")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          819,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                819,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant210"), "variant210")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          820,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                820,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant211"), "variant211")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          821,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                821,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant212"), "variant212")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          822,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                822,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant213"), "variant213")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          823,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                823,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant214"), "variant214")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          824,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                824,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant215"), "variant215")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          825,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                825,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant216"), "variant216")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          826,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                826,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant217"), "variant217")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          827,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                827,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant218"), "variant218")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          828,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                828,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant219"), "variant219")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          829,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                829,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant220"), "variant220")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          830,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                830,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant221"), "variant221")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          831,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                831,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant222"), "variant222")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          832,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                832,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant223"), "variant223")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          833,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                833,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant224"), "variant224")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          834,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                834,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant225"), "variant225")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          835,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                835,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant226"), "variant226")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          836,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                836,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant227"), "variant227")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          837,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                837,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant228"), "variant228")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          838,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                838,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant229"), "variant229")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          839,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                839,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant230"), "variant230")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          840,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                840,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant231"), "variant231")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          841,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                841,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant232"), "variant232")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          842,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                842,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant233"), "variant233")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          843,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                843,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant234"), "variant234")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          844,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                844,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant235"), "variant235")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          845,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                845,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant236"), "variant236")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          846,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                846,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant237"), "variant237")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          847,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                847,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant238"), "variant238")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          848,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                848,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant239"), "variant239")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          849,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                849,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant240"), "variant240")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          850,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                850,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant241"), "variant241")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          851,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                851,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant242"), "variant242")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          852,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                852,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant243"), "variant243")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          853,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                853,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant244"), "variant244")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          854,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                854,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant245"), "variant245")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          855,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                855,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant246"), "variant246")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          856,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                856,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant247"), "variant247")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          857,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                857,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant248"), "variant248")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          858,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                858,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant249"), "variant249")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          859,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                859,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant250"), "variant250")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          860,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                860,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant251"), "variant251")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          861,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                861,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant252"), "variant252")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          862,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                862,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant253"), "variant253")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          863,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                863,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant254"), "variant254")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          864,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                864,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant255"), "variant255")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          865,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                865,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant256"), "variant256")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          866,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                866,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant257"), "variant257")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          867,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                867,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant258"), "variant258")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          868,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                868,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant259"), "variant259")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          869,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                869,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant260"), "variant260")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          870,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                870,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant261"), "variant261")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          871,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                871,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant262"), "variant262")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          872,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                872,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant263"), "variant263")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          873,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                873,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant264"), "variant264")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          874,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                874,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant265"), "variant265")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          875,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                875,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant266"), "variant266")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          876,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                876,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant267"), "variant267")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          877,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                877,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant268"), "variant268")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          878,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                878,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant269"), "variant269")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          879,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                879,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant270"), "variant270")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          880,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                880,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant271"), "variant271")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          881,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                881,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant272"), "variant272")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          882,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                882,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant273"), "variant273")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          883,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                883,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant274"), "variant274")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          884,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                884,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant275"), "variant275")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          885,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                885,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant276"), "variant276")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          886,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                886,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant277"), "variant277")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          887,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                887,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant278"), "variant278")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          888,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                888,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant279"), "variant279")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          889,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                889,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant280"), "variant280")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          890,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                890,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant281"), "variant281")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          891,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                891,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant282"), "variant282")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          892,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                892,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant283"), "variant283")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          893,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                893,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant284"), "variant284")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          894,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                894,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant285"), "variant285")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          895,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                895,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant286"), "variant286")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          896,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                896,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant287"), "variant287")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          897,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                897,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant288"), "variant288")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          898,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                898,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant289"), "variant289")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          899,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                899,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant290"), "variant290")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          900,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                900,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant291"), "variant291")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          901,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                901,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant292"), "variant292")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          902,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                902,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant293"), "variant293")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          903,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                903,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant294"), "variant294")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          904,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                904,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant295"), "variant295")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          905,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                905,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant296"), "variant296")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          906,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                906,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant297"), "variant297")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          907,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                907,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant298"), "variant298")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          908,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                908,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("variant299"), "variant299")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          909,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                909,
+                2
+              ]
+            }
+          });
 }
 
 if (!eq(tFromJs("xx"), undefined)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/big_polyvar_test.ml",
-          910,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/big_polyvar_test.ml",
+                910,
+                2
+              ]
+            }
+          });
 }
 
 exports.tToJs = tToJs;
diff --git a/jscomp/test/dist/jscomp/test/bs_array_test.js b/jscomp/test/dist/jscomp/test/bs_array_test.js
index ce2dfa2274..71e7b2adec 100644
--- a/jscomp/test/dist/jscomp/test/bs_array_test.js
+++ b/jscomp/test/dist/jscomp/test/bs_array_test.js
@@ -137,15 +137,16 @@ var v$1 = [
 ];
 
 if (!Belt__Belt_Array.set(v$1, 0, 0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_array_test.ml",
-          38,
-          33
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_array_test.ml",
+                38,
+                33
+              ]
+            }
+          });
 }
 
 b("File \"jscomp/test/bs_array_test.ml\", line 38, characters 4-11", Belt__Belt_Array.getExn(v$1, 0) === 0);
@@ -156,15 +157,16 @@ var v$2 = [
 ];
 
 if (!Belt__Belt_Array.set(v$2, 1, 0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_array_test.ml",
-          39,
-          32
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_array_test.ml",
+                39,
+                32
+              ]
+            }
+          });
 }
 
 b("File \"jscomp/test/bs_array_test.ml\", line 39, characters 4-11", Belt__Belt_Array.getExn(v$2, 1) === 0);
@@ -279,15 +281,16 @@ function addone(x) {
 
 function makeMatrixExn(sx, sy, init) {
   if (!(sx >= 0 && sy >= 0)) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/bs_array_test.ml",
-            80,
-            2
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/bs_array_test.ml",
+                  80,
+                  2
+                ]
+              }
+            });
   }
   var res = new Array(sx);
   for(var x = 0; x < sx; ++x){
diff --git a/jscomp/test/dist/jscomp/test/bs_hashtbl_string_test.js b/jscomp/test/dist/jscomp/test/bs_hashtbl_string_test.js
index 97be2944bf..9a6f819c7e 100644
--- a/jscomp/test/dist/jscomp/test/bs_hashtbl_string_test.js
+++ b/jscomp/test/dist/jscomp/test/bs_hashtbl_string_test.js
@@ -52,15 +52,16 @@ function bench(param) {
   }
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Belt__Belt_HashMap.has(empty, i$1)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bs_hashtbl_string_test.ml",
-              50,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bs_hashtbl_string_test.ml",
+                    50,
+                    4
+                  ]
+                }
+              });
     }
     
   }
@@ -74,15 +75,16 @@ function bench2(m) {
   }
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Belt__Belt_HashMap.has(empty, String(i$1))) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bs_hashtbl_string_test.ml",
-              76,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bs_hashtbl_string_test.ml",
+                    76,
+                    4
+                  ]
+                }
+              });
     }
     
   }
@@ -92,15 +94,16 @@ function bench2(m) {
   if (empty.size === 0) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_hashtbl_string_test.ml",
-          82,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_hashtbl_string_test.ml",
+                82,
+                2
+              ]
+            }
+          });
 }
 
 function bench3(m) {
@@ -112,15 +115,16 @@ function bench3(m) {
   }
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Belt__Belt_MapDict.has(table, String(i$1), cmp)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bs_hashtbl_string_test.ml",
-              98,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bs_hashtbl_string_test.ml",
+                    98,
+                    4
+                  ]
+                }
+              });
     }
     
   }
@@ -130,15 +134,16 @@ function bench3(m) {
   if (Belt__Belt_MapDict.size(table) === 0) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_hashtbl_string_test.ml",
-          105,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_hashtbl_string_test.ml",
+                105,
+                2
+              ]
+            }
+          });
 }
 
 var Sx = Belt__Belt_Id.comparable(Caml.caml_string_compare);
@@ -150,15 +155,16 @@ function bench4(param) {
   }
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Belt__Belt_HashMapString.has(table, String(i$1))) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bs_hashtbl_string_test.ml",
-              118,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bs_hashtbl_string_test.ml",
+                    118,
+                    4
+                  ]
+                }
+              });
     }
     
   }
@@ -168,15 +174,16 @@ function bench4(param) {
   if (Belt__Belt_HashMapString.isEmpty(table)) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_hashtbl_string_test.ml",
-          124,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_hashtbl_string_test.ml",
+                124,
+                2
+              ]
+            }
+          });
 }
 
 function bench5(param) {
@@ -189,15 +196,16 @@ function bench5(param) {
   console.time("bs_hashtbl_string_test.ml 137");
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Belt__Belt_HashMap.has(table, i$1)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bs_hashtbl_string_test.ml",
-              138,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bs_hashtbl_string_test.ml",
+                    138,
+                    6
+                  ]
+                }
+              });
     }
     
   }
@@ -210,15 +218,16 @@ function bench5(param) {
   if (Belt__Belt_HashMap.isEmpty(table)) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_hashtbl_string_test.ml",
-          144,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_hashtbl_string_test.ml",
+                144,
+                2
+              ]
+            }
+          });
 }
 
 function bench6(param) {
@@ -228,15 +237,16 @@ function bench6(param) {
   }
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Belt__Belt_HashMapInt.has(table, i$1)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bs_hashtbl_string_test.ml",
-              156,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bs_hashtbl_string_test.ml",
+                    156,
+                    4
+                  ]
+                }
+              });
     }
     
   }
@@ -246,15 +256,16 @@ function bench6(param) {
   if (table.size === 0) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_hashtbl_string_test.ml",
-          162,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_hashtbl_string_test.ml",
+                162,
+                2
+              ]
+            }
+          });
 }
 
 function bench7(param) {
@@ -264,15 +275,16 @@ function bench7(param) {
   }
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Belt__Belt_HashSetInt.has(table, i$1)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bs_hashtbl_string_test.ml",
-              181,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bs_hashtbl_string_test.ml",
+                    181,
+                    4
+                  ]
+                }
+              });
     }
     
   }
@@ -282,15 +294,16 @@ function bench7(param) {
   if (table.size === 0) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_hashtbl_string_test.ml",
-          192,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_hashtbl_string_test.ml",
+                192,
+                2
+              ]
+            }
+          });
 }
 
 console.time("bs_hashtbl_string_test.ml 203");
diff --git a/jscomp/test/dist/jscomp/test/bs_queue_test.js b/jscomp/test/dist/jscomp/test/bs_queue_test.js
index ec234b5829..a9423ebb50 100644
--- a/jscomp/test/dist/jscomp/test/bs_queue_test.js
+++ b/jscomp/test/dist/jscomp/test/bs_queue_test.js
@@ -45,42 +45,45 @@ var q = {
 };
 
 if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q), []) && q.length === 0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          21,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                21,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray((Belt__Belt_MutableQueue.add(q, 1), q)), [1]) && q.length === 1)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          22,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                22,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray((Belt__Belt_MutableQueue.add(q, 2), q)), [
           1,
           2
         ]) && q.length === 2)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          23,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                23,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray((Belt__Belt_MutableQueue.add(q, 3), q)), [
@@ -88,15 +91,16 @@ if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray((Belt__Belt_MutableQue
           2,
           3
         ]) && q.length === 3)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          24,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                24,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray((Belt__Belt_MutableQueue.add(q, 4), q)), [
@@ -105,27 +109,29 @@ if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray((Belt__Belt_MutableQue
           3,
           4
         ]) && q.length === 4)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          25,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                25,
+                2
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.popExn(q) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          26,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                26,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q), [
@@ -133,102 +139,110 @@ if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q), [
           3,
           4
         ]) && q.length === 3)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          26,
-          27
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                26,
+                27
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.popExn(q) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          27,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                27,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q), [
           3,
           4
         ]) && q.length === 2)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          27,
-          27
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                27,
+                27
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.popExn(q) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          28,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                28,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q), [4]) && q.length === 1)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          28,
-          27
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                28,
+                27
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.popExn(q) !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          29,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                29,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q), []) && q.length === 0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          29,
-          27
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                29,
+                27
+              ]
+            }
+          });
 }
 
 if (!does_raise(Belt__Belt_MutableQueue.popExn, q)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          30,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                30,
+                2
+              ]
+            }
+          });
 }
 
 var q$1 = {
@@ -238,63 +252,68 @@ var q$1 = {
 };
 
 if (Belt__Belt_MutableQueue.popExn((Belt__Belt_MutableQueue.add(q$1, 1), q$1)) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          35,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                35,
+                2
+              ]
+            }
+          });
 }
 
 if (!does_raise(Belt__Belt_MutableQueue.popExn, q$1)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          35,
-          34
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                35,
+                34
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.popExn((Belt__Belt_MutableQueue.add(q$1, 2), q$1)) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          36,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                36,
+                2
+              ]
+            }
+          });
 }
 
 if (!does_raise(Belt__Belt_MutableQueue.popExn, q$1)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          36,
-          34
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                36,
+                34
+              ]
+            }
+          });
 }
 
 if (q$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          37,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                37,
+                2
+              ]
+            }
+          });
 }
 
 var q$2 = {
@@ -304,135 +323,146 @@ var q$2 = {
 };
 
 if (Belt__Belt_MutableQueue.peekExn((Belt__Belt_MutableQueue.add(q$2, 1), q$2)) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          42,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                42,
+                2
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.peekExn((Belt__Belt_MutableQueue.add(q$2, 2), q$2)) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          43,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                43,
+                2
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.peekExn((Belt__Belt_MutableQueue.add(q$2, 3), q$2)) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          44,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                44,
+                2
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.peekExn(q$2) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          45,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                45,
+                2
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.popExn(q$2) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          45,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                45,
+                28
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.peekExn(q$2) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          46,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                46,
+                2
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.popExn(q$2) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          46,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                46,
+                28
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.peekExn(q$2) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          47,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                47,
+                2
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.popExn(q$2) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          47,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                47,
+                28
+              ]
+            }
+          });
 }
 
 if (!does_raise(Belt__Belt_MutableQueue.peekExn, q$2)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          48,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                48,
+                2
+              ]
+            }
+          });
 }
 
 if (!does_raise(Belt__Belt_MutableQueue.peekExn, q$2)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          49,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                49,
+                2
+              ]
+            }
+          });
 }
 
 var q$3 = {
@@ -448,27 +478,29 @@ for(var i = 1; i <= 10; ++i){
 Belt__Belt_MutableQueue.clear(q$3);
 
 if (q$3.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          56,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                56,
+                2
+              ]
+            }
+          });
 }
 
 if (!does_raise(Belt__Belt_MutableQueue.popExn, q$3)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          57,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                57,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(q$3, {
@@ -476,29 +508,31 @@ if (!Caml_obj.caml_equal(q$3, {
         first: undefined,
         last: undefined
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          58,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                58,
+                2
+              ]
+            }
+          });
 }
 
 Belt__Belt_MutableQueue.add(q$3, 42);
 
 if (Belt__Belt_MutableQueue.popExn(q$3) !== 42) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          60,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                60,
+                2
+              ]
+            }
+          });
 }
 
 var q1 = {
@@ -525,15 +559,16 @@ if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1), [
         9,
         10
       ])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          67,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                67,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2), [
@@ -548,67 +583,72 @@ if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2), [
         9,
         10
       ])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          68,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                68,
+                2
+              ]
+            }
+          });
 }
 
 if (q1.length !== 10) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          69,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                69,
+                2
+              ]
+            }
+          });
 }
 
 if (q2.length !== 10) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          70,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                70,
+                2
+              ]
+            }
+          });
 }
 
 for(var i$2 = 1; i$2 <= 10; ++i$2){
   if (Belt__Belt_MutableQueue.popExn(q1) !== i$2) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/bs_queue_test.ml",
-            72,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/bs_queue_test.ml",
+                  72,
+                  4
+                ]
+              }
+            });
   }
   
 }
 
 for(var i$3 = 1; i$3 <= 10; ++i$3){
   if (Belt__Belt_MutableQueue.popExn(q2) !== i$3) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/bs_queue_test.ml",
-            75,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/bs_queue_test.ml",
+                  75,
+                  4
+                ]
+              }
+            });
   }
   
 }
@@ -620,92 +660,99 @@ var q$4 = {
 };
 
 if (q$4.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          81,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                81,
+                2
+              ]
+            }
+          });
 }
 
 for(var i$4 = 1; i$4 <= 10; ++i$4){
   Belt__Belt_MutableQueue.add(q$4, i$4);
   if (q$4.length !== i$4) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/bs_queue_test.ml",
-            84,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/bs_queue_test.ml",
+                  84,
+                  4
+                ]
+              }
+            });
   }
   if (q$4.length === 0) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/bs_queue_test.ml",
-            85,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/bs_queue_test.ml",
+                  85,
+                  4
+                ]
+              }
+            });
   }
   
 }
 
 for(var i$5 = 10; i$5 >= 1; --i$5){
   if (q$4.length !== i$5) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/bs_queue_test.ml",
-            88,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/bs_queue_test.ml",
+                  88,
+                  4
+                ]
+              }
+            });
   }
   if (q$4.length === 0) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/bs_queue_test.ml",
-            89,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/bs_queue_test.ml",
+                  89,
+                  4
+                ]
+              }
+            });
   }
   Belt__Belt_MutableQueue.popExn(q$4);
 }
 
 if (q$4.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          92,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                92,
+                2
+              ]
+            }
+          });
 }
 
 if (q$4.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          93,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                93,
+                2
+              ]
+            }
+          });
 }
 
 var q$5 = {
@@ -724,15 +771,16 @@ var i$7 = {
 
 Belt__Belt_MutableQueue.forEach(q$5, (function (j) {
         if (i$7.contents !== j) {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/bs_queue_test.ml",
-                  100,
-                  24
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/bs_queue_test.ml",
+                        100,
+                        24
+                      ]
+                    }
+                  });
         }
         i$7.contents = i$7.contents + 1 | 0;
       }));
@@ -750,101 +798,109 @@ var q2$1 = {
 };
 
 if (q1$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          105,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                105,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$1), [])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          105,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                105,
+                26
+              ]
+            }
+          });
 }
 
 if (q2$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          106,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                106,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$1), [])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          106,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                106,
+                26
+              ]
+            }
+          });
 }
 
 Belt__Belt_MutableQueue.transfer(q1$1, q2$1);
 
 if (q1$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          108,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                108,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$1), [])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          108,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                108,
+                26
+              ]
+            }
+          });
 }
 
 if (q2$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          109,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                109,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$1), [])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          109,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                109,
+                26
+              ]
+            }
+          });
 }
 
 var q1$2 = {
@@ -864,15 +920,16 @@ for(var i$8 = 1; i$8 <= 4; ++i$8){
 }
 
 if (q1$2.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          115,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                115,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$2), [
@@ -881,77 +938,83 @@ if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$2), [
         3,
         4
       ])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          115,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                115,
+                26
+              ]
+            }
+          });
 }
 
 if (q2$2.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          116,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                116,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$2), [])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          116,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                116,
+                26
+              ]
+            }
+          });
 }
 
 Belt__Belt_MutableQueue.transfer(q1$2, q2$2);
 
 if (q1$2.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          118,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                118,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$2), [])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          118,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                118,
+                26
+              ]
+            }
+          });
 }
 
 if (q2$2.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          119,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                119,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$2), [
@@ -960,15 +1023,16 @@ if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$2), [
         3,
         4
       ])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          119,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                119,
+                26
+              ]
+            }
+          });
 }
 
 var q1$3 = {
@@ -988,39 +1052,42 @@ for(var i$9 = 5; i$9 <= 8; ++i$9){
 }
 
 if (q1$3.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          125,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                125,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$3), [])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          125,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                125,
+                26
+              ]
+            }
+          });
 }
 
 if (q2$3.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          126,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                126,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$3), [
@@ -1029,53 +1096,57 @@ if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$3), [
         7,
         8
       ])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          126,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                126,
+                26
+              ]
+            }
+          });
 }
 
 Belt__Belt_MutableQueue.transfer(q1$3, q2$3);
 
 if (q1$3.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          128,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                128,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$3), [])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          128,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                128,
+                26
+              ]
+            }
+          });
 }
 
 if (q2$3.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          129,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                129,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$3), [
@@ -1084,15 +1155,16 @@ if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$3), [
         7,
         8
       ])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          129,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                129,
+                26
+              ]
+            }
+          });
 }
 
 var q1$4 = {
@@ -1116,15 +1188,16 @@ for(var i$11 = 5; i$11 <= 8; ++i$11){
 }
 
 if (q1$4.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          136,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                136,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$4), [
@@ -1133,27 +1206,29 @@ if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$4), [
         3,
         4
       ])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          136,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                136,
+                26
+              ]
+            }
+          });
 }
 
 if (q2$4.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          137,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                137,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$4), [
@@ -1162,41 +1237,44 @@ if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$4), [
         7,
         8
       ])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          137,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                137,
+                26
+              ]
+            }
+          });
 }
 
 Belt__Belt_MutableQueue.transfer(q1$4, q2$4);
 
 if (q1$4.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          139,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                139,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q1$4), [])) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          139,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                139,
+                26
+              ]
+            }
+          });
 }
 
 var v = [
@@ -1211,27 +1289,29 @@ var v = [
 ];
 
 if (q2$4.length !== 8) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          141,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                141,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Belt__Belt_MutableQueue.toArray(q2$4), v)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          141,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                141,
+                26
+              ]
+            }
+          });
 }
 
 if (Belt__Belt_MutableQueue.reduce(q2$4, 0, (function (x, y) {
@@ -1239,15 +1319,16 @@ if (Belt__Belt_MutableQueue.reduce(q2$4, 0, (function (x, y) {
         })) !== Belt__Belt_Array.reduce(v, 0, (function (x, y) {
           return x - y | 0;
         }))) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_queue_test.ml",
-          143,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_queue_test.ml",
+                143,
+                2
+              ]
+            }
+          });
 }
 
 console.log("OK");
diff --git a/jscomp/test/dist/jscomp/test/bs_rbset_int_bench.js b/jscomp/test/dist/jscomp/test/bs_rbset_int_bench.js
index f64cadb1a6..cb3c9f425a 100644
--- a/jscomp/test/dist/jscomp/test/bs_rbset_int_bench.js
+++ b/jscomp/test/dist/jscomp/test/bs_rbset_int_bench.js
@@ -13,15 +13,16 @@ function bench(param) {
   console.time("bs_rbset_int_bench.ml 11");
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Rbset.mem(i$1, data)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bs_rbset_int_bench.ml",
-              12,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bs_rbset_int_bench.ml",
+                    12,
+                    4
+                  ]
+                }
+              });
     }
     
   }
@@ -34,15 +35,16 @@ function bench(param) {
   if (Rbset.cardinal(data) === 0) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_rbset_int_bench.ml",
-          17,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_rbset_int_bench.ml",
+                17,
+                2
+              ]
+            }
+          });
 }
 
 console.time("bs_rbset_int_bench.ml 21");
diff --git a/jscomp/test/dist/jscomp/test/bs_set_bench.js b/jscomp/test/dist/jscomp/test/bs_set_bench.js
index 9acad395cc..6c99dbac06 100644
--- a/jscomp/test/dist/jscomp/test/bs_set_bench.js
+++ b/jscomp/test/dist/jscomp/test/bs_set_bench.js
@@ -13,15 +13,16 @@ function bench(param) {
   console.time("bs_set_bench.ml 11");
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Belt__Belt_SetInt.has(data, i$1)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/bs_set_bench.ml",
-              12,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/bs_set_bench.ml",
+                    12,
+                    4
+                  ]
+                }
+              });
     }
     
   }
@@ -34,15 +35,16 @@ function bench(param) {
   if (Belt__Belt_SetInt.size(data) === 0) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/bs_set_bench.ml",
-          17,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/bs_set_bench.ml",
+                17,
+                2
+              ]
+            }
+          });
 }
 
 console.time("bs_set_bench.ml 21");
diff --git a/jscomp/test/dist/jscomp/test/caml_sys_poly_fill_test.js b/jscomp/test/dist/jscomp/test/caml_sys_poly_fill_test.js
index fa21c65bfb..f465a723f7 100644
--- a/jscomp/test/dist/jscomp/test/caml_sys_poly_fill_test.js
+++ b/jscomp/test/dist/jscomp/test/caml_sys_poly_fill_test.js
@@ -57,7 +57,9 @@ catch (raw_exn){
   if (exn.MEL_EXN_ID === Stdlib.Not_found) {
     tmp = "Z";
   } else {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/chn_test.js b/jscomp/test/dist/jscomp/test/chn_test.js
index d6e689a3c8..08f6004dfa 100644
--- a/jscomp/test/dist/jscomp/test/chn_test.js
+++ b/jscomp/test/dist/jscomp/test/chn_test.js
@@ -40,15 +40,16 @@ function convert(s) {
                     if (x$1 !== undefined) {
                       return x$1;
                     }
-                    throw {
-                          MEL_EXN_ID: "Assert_failure",
-                          _1: [
-                            "jscomp/test/chn_test.ml",
-                            20,
-                            22
-                          ],
-                          Error: new Error()
-                        };
+                    throw new Error("Assert_failure", {
+                              cause: {
+                                MEL_EXN_ID: "Assert_failure",
+                                _1: [
+                                  "jscomp/test/chn_test.ml",
+                                  20,
+                                  22
+                                ]
+                              }
+                            });
                   })));
 }
 
diff --git a/jscomp/test/dist/jscomp/test/class6_test.js b/jscomp/test/dist/jscomp/test/class6_test.js
index 1ac872bd87..86d379bd13 100644
--- a/jscomp/test/dist/jscomp/test/class6_test.js
+++ b/jscomp/test/dist/jscomp/test/class6_test.js
@@ -116,10 +116,11 @@ function lookup_obj(obj, _param) {
       _param = param.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/class_fib_open_recursion_test.js b/jscomp/test/dist/jscomp/test/class_fib_open_recursion_test.js
index a85c0778be..1a14d42164 100644
--- a/jscomp/test/dist/jscomp/test/class_fib_open_recursion_test.js
+++ b/jscomp/test/dist/jscomp/test/class_fib_open_recursion_test.js
@@ -70,7 +70,9 @@ function memo_fib_init($$class) {
               Stdlib__Hashtbl.add(self$2[cache], x, v);
               return v;
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }));
   return function (env, self) {
diff --git a/jscomp/test/dist/jscomp/test/class_repr.js b/jscomp/test/dist/jscomp/test/class_repr.js
index 7e81b215d6..2076479c33 100644
--- a/jscomp/test/dist/jscomp/test/class_repr.js
+++ b/jscomp/test/dist/jscomp/test/class_repr.js
@@ -49,27 +49,29 @@ var v = Curry._2(x[0], undefined, 3);
 var u = Caml_oo.caml_set_oo_id(Caml_obj.caml_obj_dup(v));
 
 if (Caml_oo_curry.js1(291546447, 1, v) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/class_repr.ml",
-          28,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/class_repr.ml",
+                28,
+                9
+              ]
+            }
+          });
 }
 
 if (Caml_oo_curry.js1(291546447, 2, u) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/class_repr.ml",
-          30,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/class_repr.ml",
+                30,
+                9
+              ]
+            }
+          });
 }
 
 function xx_init($$class) {
@@ -105,15 +107,16 @@ var v1 = Curry._2(xx[0], undefined, 3);
 var v2 = Caml_oo_curry.js1(-977586732, 3, v1);
 
 if (Caml_oo_curry.js1(-804710761, 4, v1) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/class_repr.ml",
-          42,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/class_repr.ml",
+                42,
+                9
+              ]
+            }
+          });
 }
 
 if (typeof Stdlib__Sys.backend_type !== "number" && Stdlib__Sys.backend_type._0 === "Melange") {
@@ -124,15 +127,16 @@ if (typeof Stdlib__Sys.backend_type !== "number" && Stdlib__Sys.backend_type._0
 }
 
 if (Caml_oo_curry.js1(-804710761, 9, v2) !== 9) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/class_repr.ml",
-          57,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/class_repr.ml",
+                57,
+                9
+              ]
+            }
+          });
 }
 
 function point_init($$class) {
@@ -168,15 +172,16 @@ var point = CamlinternalOO.make_class([
 var v$1 = Curry._1(point[0], undefined);
 
 if (Caml_oo_curry.js1(590348294, 10, v$1) !== 5) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/class_repr.ml",
-          104,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/class_repr.ml",
+                104,
+                2
+              ]
+            }
+          });
 }
 
 function xx0_init($$class) {
diff --git a/jscomp/test/dist/jscomp/test/const_defs_test.js b/jscomp/test/dist/jscomp/test/const_defs_test.js
index 4504b11731..56778ba060 100644
--- a/jscomp/test/dist/jscomp/test/const_defs_test.js
+++ b/jscomp/test/dist/jscomp/test/const_defs_test.js
@@ -5,11 +5,12 @@
 var u = 3;
 
 function f(param) {
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "hi",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "hi"
+            }
+          });
 }
 
 exports.u = u;
diff --git a/jscomp/test/dist/jscomp/test/custom_error_test.js b/jscomp/test/dist/jscomp/test/custom_error_test.js
index 0e8865fee1..92bddaa587 100644
--- a/jscomp/test/dist/jscomp/test/custom_error_test.js
+++ b/jscomp/test/dist/jscomp/test/custom_error_test.js
@@ -16,7 +16,9 @@ function test_js_error(param) {
       console.log(exn._1.stack);
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return Caml_option.some(e);
 }
@@ -29,9 +31,13 @@ function test_js_error2(param) {
     var e = Caml_js_exceptions.internalToOCamlException(raw_e);
     if (e.MEL_EXN_ID === Js__Js_exn.$$Error) {
       console.log(e._1.stack);
-      throw e;
+      throw new Error(e.MEL_EXN_ID, {
+                cause: e
+              });
     }
-    throw e;
+    throw new Error(e.MEL_EXN_ID, {
+              cause: e
+            });
   }
 }
 
@@ -46,7 +52,9 @@ function example1(param) {
       console.log(exn._1.stack);
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return Caml_option.some(v);
 }
@@ -60,7 +68,9 @@ function example2(param) {
     if (exn.MEL_EXN_ID === Js__Js_exn.$$Error) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/defunctor_make_test.js b/jscomp/test/dist/jscomp/test/defunctor_make_test.js
index 2019042b09..df5d7c7825 100644
--- a/jscomp/test/dist/jscomp/test/defunctor_make_test.js
+++ b/jscomp/test/dist/jscomp/test/defunctor_make_test.js
@@ -51,17 +51,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -83,17 +85,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add(x, data, compare, param) {
diff --git a/jscomp/test/dist/jscomp/test/demo_int_map.js b/jscomp/test/dist/jscomp/test/demo_int_map.js
index afd98df9e8..7d3417f0a1 100644
--- a/jscomp/test/dist/jscomp/test/demo_int_map.js
+++ b/jscomp/test/dist/jscomp/test/demo_int_map.js
@@ -47,17 +47,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -79,17 +81,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add(x, data, m) {
@@ -147,10 +151,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/earger_curry_test.js b/jscomp/test/dist/jscomp/test/earger_curry_test.js
index 694970c4bf..9dd7215d07 100644
--- a/jscomp/test/dist/jscomp/test/earger_curry_test.js
+++ b/jscomp/test/dist/jscomp/test/earger_curry_test.js
@@ -25,11 +25,12 @@ function init(l, f) {
     return [];
   }
   if (l < 0) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Array.init",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Array.init"
+              }
+            });
   }
   var res = Caml_array.make(l, f$1(0));
   for(var i = 1; i < l; ++i){
diff --git a/jscomp/test/dist/jscomp/test/equal_exception_test.js b/jscomp/test/dist/jscomp/test/equal_exception_test.js
index 21c8eac24c..80bc63eef7 100644
--- a/jscomp/test/dist/jscomp/test/equal_exception_test.js
+++ b/jscomp/test/dist/jscomp/test/equal_exception_test.js
@@ -13,56 +13,62 @@ var v = "gso";
 
 function is_equal(param) {
   if (Caml_bytes.get(Stdlib__Bytes.make(3, /* 'a' */97), 0) !== /* 'a' */97) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/equal_exception_test.ml",
-            9,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/equal_exception_test.ml",
+                  9,
+                  4
+                ]
+              }
+            });
   }
   if (Stdlib__Bytes.make(3, /* 'a' */97)[0] !== /* 'a' */97) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/equal_exception_test.ml",
-            10,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/equal_exception_test.ml",
+                  10,
+                  4
+                ]
+              }
+            });
   }
   var u = Stdlib__Bytes.make(3, /* 'a' */97);
   u[0] = /* 'b' */98;
   if (u[0] !== /* 'b' */98) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/equal_exception_test.ml",
-            13,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/equal_exception_test.ml",
+                  13,
+                  4
+                ]
+              }
+            });
   }
   
 }
 
 function is_exception(param) {
   try {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -73,7 +79,9 @@ function is_normal_exception(_x) {
     _1: 3
   };
   try {
-    throw v;
+    throw new Error(v.MEL_EXN_ID, {
+              cause: v
+            });
   }
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
@@ -81,19 +89,24 @@ function is_normal_exception(_x) {
       if (exn._1 === 3) {
         return ;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
 function is_arbitrary_exception(param) {
   var A = /* @__PURE__ */Caml_exceptions.create("A");
   try {
-    throw {
-          MEL_EXN_ID: A,
-          Error: new Error()
-        };
+    throw new Error(A, {
+              cause: {
+                MEL_EXN_ID: A
+              }
+            });
   }
   catch (exn){
     return ;
@@ -143,27 +156,29 @@ var Not_found = /* @__PURE__ */Caml_exceptions.create("Equal_exception_test.Not_
 if (Caml_obj.caml_equal(e, {
         MEL_EXN_ID: Not_found
       }) !== false) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/equal_exception_test.ml",
-          50,
-          3
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/equal_exception_test.ml",
+                50,
+                3
+              ]
+            }
+          });
 }
 
 if (Not_found === Stdlib.Not_found !== false) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/equal_exception_test.ml",
-          51,
-          3
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/equal_exception_test.ml",
+                51,
+                3
+              ]
+            }
+          });
 }
 
 Mt.from_suites("exception", suites);
diff --git a/jscomp/test/dist/jscomp/test/exception_raise_test.js b/jscomp/test/dist/jscomp/test/exception_raise_test.js
index 4e52223981..cc808e33b3 100644
--- a/jscomp/test/dist/jscomp/test/exception_raise_test.js
+++ b/jscomp/test/dist/jscomp/test/exception_raise_test.js
@@ -105,15 +105,16 @@ catch (raw_exn$3){
   if (exn$3.MEL_EXN_ID === A || exn$3.MEL_EXN_ID === Js__Js_exn.$$Error) {
     a0 = exn$3._1;
   } else {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/exception_raise_test.ml",
-            102,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/exception_raise_test.ml",
+                  102,
+                  9
+                ]
+              }
+            });
   }
 }
 
@@ -170,15 +171,16 @@ var suites = {
                       _1: 2
                     };
             }
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/exception_raise_test.ml",
-                    119,
-                    15
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/exception_raise_test.ml",
+                          119,
+                          15
+                        ]
+                      }
+                    });
           })
       ],
       tl: /* [] */0
@@ -204,10 +206,11 @@ catch (raw_e$2){
 }
 
 try {
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 catch (raw_e$3){
   var e$1 = Caml_js_exceptions.internalToOCamlException(raw_e$3);
diff --git a/jscomp/test/dist/jscomp/test/exception_rebound_err_test.js b/jscomp/test/dist/jscomp/test/exception_rebound_err_test.js
index 96263d1cbb..615c989965 100644
--- a/jscomp/test/dist/jscomp/test/exception_rebound_err_test.js
+++ b/jscomp/test/dist/jscomp/test/exception_rebound_err_test.js
@@ -76,7 +76,9 @@ function f(g) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return 1;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/exception_value_test.js b/jscomp/test/dist/jscomp/test/exception_value_test.js
index f384550f2d..bc5fb10485 100644
--- a/jscomp/test/dist/jscomp/test/exception_value_test.js
+++ b/jscomp/test/dist/jscomp/test/exception_value_test.js
@@ -8,32 +8,35 @@ var Js__Js_exn = require("melange.js/js_exn.js");
 var Stdlib = require("melange/stdlib.js");
 
 function f(param) {
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function assert_f(x) {
   if (x <= 3) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/exception_value_test.ml",
-            9,
-            12
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/exception_value_test.ml",
+                  9,
+                  12
+                ]
+              }
+            });
   }
   return 3;
 }
 
 function hh(param) {
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 var A = /* @__PURE__ */Caml_exceptions.create("Exception_value_test.A");
@@ -56,7 +59,9 @@ function test_not_found(f, param) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return 2;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -68,9 +73,13 @@ function test_js_error2(param) {
     var e = Caml_js_exceptions.internalToOCamlException(raw_e);
     if (e.MEL_EXN_ID === Js__Js_exn.$$Error) {
       console.log(e._1.stack);
-      throw e;
+      throw new Error(e.MEL_EXN_ID, {
+                cause: e
+              });
     }
-    throw e;
+    throw new Error(e.MEL_EXN_ID, {
+              cause: e
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/exn_error_pattern.js b/jscomp/test/dist/jscomp/test/exn_error_pattern.js
index eae775f530..82c3c7fef1 100644
--- a/jscomp/test/dist/jscomp/test/exn_error_pattern.js
+++ b/jscomp/test/dist/jscomp/test/exn_error_pattern.js
@@ -73,7 +73,9 @@ eq("File \"jscomp/test/exn_error_pattern.ml\", line 33, characters 5-12", f({
 var tmp;
 
 try {
-  throw new Error("x");
+  throw new Error(new Error("x").MEL_EXN_ID, {
+            cause: new Error("x")
+          });
 }
 catch (raw_e){
   tmp = Caml_js_exceptions.internalToOCamlException(raw_e);
diff --git a/jscomp/test/dist/jscomp/test/ext_array_test.js b/jscomp/test/dist/jscomp/test/ext_array_test.js
index 7898765162..0bfe6b035d 100644
--- a/jscomp/test/dist/jscomp/test/ext_array_test.js
+++ b/jscomp/test/dist/jscomp/test/ext_array_test.js
@@ -106,11 +106,12 @@ function filter_map(f, a) {
 
 function range(from, to_) {
   if (from > to_) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_array_test.range",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_array_test.range"
+              }
+            });
   }
   return Stdlib__Array.init((to_ - from | 0) + 1 | 0, (function (i) {
                 return i + from | 0;
@@ -120,11 +121,12 @@ function range(from, to_) {
 function map2i(f, a, b) {
   var len = a.length;
   if (len !== b.length) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_array_test.map2i",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_array_test.map2i"
+              }
+            });
   }
   return Stdlib__Array.mapi((function (i, a) {
                 return Curry._3(f, i, a, b[i]);
diff --git a/jscomp/test/dist/jscomp/test/ext_bytes_test.js b/jscomp/test/dist/jscomp/test/ext_bytes_test.js
index aab299f06e..785da8b8da 100644
--- a/jscomp/test/dist/jscomp/test/ext_bytes_test.js
+++ b/jscomp/test/dist/jscomp/test/ext_bytes_test.js
@@ -137,10 +137,11 @@ function starts_with(xs, prefix, p) {
   try {
     for(var i = 0; i < len2; ++i){
       if (!Curry._2(p, Caml_bytes.get(xs, i), Caml_bytes.get(prefix, i))) {
-        throw {
-              MEL_EXN_ID: H,
-              Error: new Error()
-            };
+        throw new Error(H, {
+                  cause: {
+                    MEL_EXN_ID: H
+                  }
+                });
       }
       
     }
@@ -151,7 +152,9 @@ function starts_with(xs, prefix, p) {
     if (exn.MEL_EXN_ID === H) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/ext_filename_test.js b/jscomp/test/dist/jscomp/test/ext_filename_test.js
index c63fd0bab7..d0321ae4d1 100644
--- a/jscomp/test/dist/jscomp/test/ext_filename_test.js
+++ b/jscomp/test/dist/jscomp/test/ext_filename_test.js
@@ -96,7 +96,9 @@ function chop_extension(locOpt, name) {
                       _1: "Filename.chop_extension ( %s : %s )"
                     }), loc, name);
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -109,7 +111,9 @@ function chop_extension_if_any(fname) {
     if (exn.MEL_EXN_ID === Stdlib.Invalid_argument) {
       return fname;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -394,11 +398,12 @@ if (Stdlib__Sys.unix) {
   simple_convert_node_path_to_os_path = Ext_string_test.replace_slash_backward;
 } else {
   var s = "Unknown OS : " + Stdlib__Sys.os_type;
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: s,
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: s
+            }
+          });
 }
 
 var $slash$slash = Stdlib__Filename.concat;
diff --git a/jscomp/test/dist/jscomp/test/ext_list_test.js b/jscomp/test/dist/jscomp/test/ext_list_test.js
index 056ba4ab43..59d0f4803d 100644
--- a/jscomp/test/dist/jscomp/test/ext_list_test.js
+++ b/jscomp/test/dist/jscomp/test/ext_list_test.js
@@ -205,20 +205,22 @@ function filter_map2(f, _xs, _ys) {
         _xs = us;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Ext_list_test.filter_map2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Ext_list_test.filter_map2"
+                }
+              });
     }
     if (!ys) {
       return /* [] */0;
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_list_test.filter_map2",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_list_test.filter_map2"
+              }
+            });
   };
 }
 
@@ -244,20 +246,22 @@ function filter_map2i(f, xs, ys) {
           _i = i + 1 | 0;
           continue ;
         }
-        throw {
-              MEL_EXN_ID: "Invalid_argument",
-              _1: "Ext_list_test.filter_map2i",
-              Error: new Error()
-            };
+        throw new Error("Invalid_argument", {
+                  cause: {
+                    MEL_EXN_ID: "Invalid_argument",
+                    _1: "Ext_list_test.filter_map2i"
+                  }
+                });
       }
       if (!ys) {
         return /* [] */0;
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Ext_list_test.filter_map2i",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Ext_list_test.filter_map2i"
+                }
+              });
     };
   };
   return aux(0, xs, ys);
@@ -294,18 +298,20 @@ function flat_map2(f, lx, ly) {
         _acc = Stdlib__List.rev_append(Curry._2(f, lx$1.hd, ly$1.hd), acc);
         continue ;
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Ext_list_test.flat_map2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Ext_list_test.flat_map2"
+                }
+              });
     }
     if (ly$1) {
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Ext_list_test.flat_map2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Ext_list_test.flat_map2"
+                }
+              });
     }
     return Stdlib__List.rev(acc);
   };
@@ -346,11 +352,12 @@ function map2_last(f, l1, l2) {
         }
         
       } else {
-        throw {
-              MEL_EXN_ID: "Invalid_argument",
-              _1: "List.map2_last",
-              Error: new Error()
-            };
+        throw new Error("Invalid_argument", {
+                  cause: {
+                    MEL_EXN_ID: "Invalid_argument",
+                    _1: "List.map2_last"
+                  }
+                });
       }
     }
     if (l2) {
@@ -360,20 +367,22 @@ function map2_last(f, l1, l2) {
               tl: map2_last(f, l1$1, l2.tl)
             };
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.map2_last",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.map2_last"
+              }
+            });
   }
   if (!l2) {
     return /* [] */0;
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "List.map2_last",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "List.map2_last"
+            }
+          });
 }
 
 function map_last(f, l1) {
@@ -405,28 +414,31 @@ function fold_right2_last(f, l1, l2, accu) {
         }
         
       } else {
-        throw {
-              MEL_EXN_ID: "Invalid_argument",
-              _1: "List.fold_right2",
-              Error: new Error()
-            };
+        throw new Error("Invalid_argument", {
+                  cause: {
+                    MEL_EXN_ID: "Invalid_argument",
+                    _1: "List.fold_right2"
+                  }
+                });
       }
     }
     if (l2) {
       return Curry._4(f, false, last1, l2.hd, fold_right2_last(f, l1$1, l2.tl, accu));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.fold_right2"
+              }
+            });
   }
   if (l2) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.fold_right2"
+              }
+            });
   }
   return accu;
 }
@@ -439,11 +451,12 @@ function take(n, l) {
   var arr = Stdlib__Array.of_list(l);
   var arr_length = arr.length;
   if (arr_length < n) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_list_test.take",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_list_test.take"
+              }
+            });
   }
   return [
           Stdlib__Array.to_list(Stdlib__Array.sub(arr, 0, n)),
@@ -526,11 +539,12 @@ function exclude_tail(x) {
       };
       continue ;
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_list_test.exclude_tail",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_list_test.exclude_tail"
+              }
+            });
   };
 }
 
@@ -579,21 +593,23 @@ function drop(_n, _h) {
     var h = _h;
     var n = _n;
     if (n < 0) {
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Ext_list_test.drop",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Ext_list_test.drop"
+                }
+              });
     }
     if (n === 0) {
       return h;
     }
     if (Caml_obj.caml_equal(h, /* [] */0)) {
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Ext_list_test.drop",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Ext_list_test.drop"
+                }
+              });
     }
     _h = Stdlib__List.tl(h);
     _n = n - 1 | 0;
@@ -762,22 +778,24 @@ function reduce_from_right(fn, lst) {
                   return Curry._2(fn, y, x);
                 }), match.hd, match.tl);
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Ext_list_test.reduce",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Ext_list_test.reduce"
+            }
+          });
 }
 
 function reduce_from_left(fn, lst) {
   if (lst) {
     return Stdlib__List.fold_left(fn, lst.hd, lst.tl);
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Ext_list_test.reduce_from_left",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Ext_list_test.reduce_from_left"
+            }
+          });
 }
 
 function create_ref_empty(param) {
@@ -791,11 +809,12 @@ function ref_top(x) {
   if (match) {
     return match.hd;
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Ext_list_test.ref_top",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Ext_list_test.ref_top"
+            }
+          });
 }
 
 function ref_empty(x) {
@@ -820,11 +839,12 @@ function ref_pop(refs) {
     refs.contents = match.tl;
     return match.hd;
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Ext_list_test.ref_pop",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Ext_list_test.ref_pop"
+            }
+          });
 }
 
 function rev_except_last(xs) {
@@ -848,11 +868,12 @@ function rev_except_last(xs) {
       };
       continue ;
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_list_test.rev_except_last",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_list_test.rev_except_last"
+              }
+            });
   };
 }
 
@@ -872,11 +893,12 @@ function last(_xs) {
       _xs = xs.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_list_test.last",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_list_test.last"
+              }
+            });
   };
 }
 
@@ -894,15 +916,16 @@ function assoc_by_string(def, k, _lst) {
     if (def !== undefined) {
       return Caml_option.valFromOption(def);
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ext_list_test.ml",
-            399,
-            14
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ext_list_test.ml",
+                  399,
+                  14
+                ]
+              }
+            });
   };
 }
 
@@ -920,15 +943,16 @@ function assoc_by_int(def, k, _lst) {
     if (def !== undefined) {
       return Caml_option.valFromOption(def);
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ext_list_test.ml",
-            409,
-            14
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ext_list_test.ml",
+                  409,
+                  14
+                ]
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/ext_pervasives_test.js b/jscomp/test/dist/jscomp/test/ext_pervasives_test.js
index 536e6ca31e..0511a82604 100644
--- a/jscomp/test/dist/jscomp/test/ext_pervasives_test.js
+++ b/jscomp/test/dist/jscomp/test/ext_pervasives_test.js
@@ -16,7 +16,9 @@ function $$finally(v, action, f) {
   }
   catch (e$1){
     Curry._1(action, v);
-    throw e$1;
+    throw new Error(e$1.MEL_EXN_ID, {
+              cause: e$1
+            });
   }
   Curry._1(action, v);
   return e;
@@ -54,10 +56,11 @@ function is_pos_pow(n) {
         _c = c + 1 | 0;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: E,
-            Error: new Error()
-          };
+      throw new Error(E, {
+                cause: {
+                  MEL_EXN_ID: E
+                }
+              });
     };
   }
   catch (raw_exn){
@@ -65,18 +68,21 @@ function is_pos_pow(n) {
     if (exn.MEL_EXN_ID === E) {
       return -1;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
 function failwithf(loc, fmt) {
   return Stdlib__Format.ksprintf((function (s) {
                 var s$1 = loc + s;
-                throw {
-                      MEL_EXN_ID: "Failure",
-                      _1: s$1,
-                      Error: new Error()
-                    };
+                throw new Error("Failure", {
+                          cause: {
+                            MEL_EXN_ID: "Failure",
+                            _1: s$1
+                          }
+                        });
               }), fmt);
 }
 
@@ -86,11 +92,12 @@ function invalid_argf(fmt) {
 
 function bad_argf(fmt) {
   return Stdlib__Format.ksprintf((function (x) {
-                throw {
-                      MEL_EXN_ID: Stdlib__Arg.Bad,
-                      _1: x,
-                      Error: new Error()
-                    };
+                throw new Error(Stdlib__Arg.Bad, {
+                          cause: {
+                            MEL_EXN_ID: Stdlib__Arg.Bad,
+                            _1: x
+                          }
+                        });
               }), fmt);
 }
 
diff --git a/jscomp/test/dist/jscomp/test/ext_string_test.js b/jscomp/test/dist/jscomp/test/ext_string_test.js
index 838a21d560..6c93fad7b8 100644
--- a/jscomp/test/dist/jscomp/test/ext_string_test.js
+++ b/jscomp/test/dist/jscomp/test/ext_string_test.js
@@ -218,11 +218,12 @@ function unsafe_for_all_range(s, _start, finish, p) {
 function for_all_range(s, start, finish, p) {
   var len = s.length;
   if (start < 0 || finish >= len) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_string_test.for_all_range",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_string_test.for_all_range"
+              }
+            });
   }
   return unsafe_for_all_range(s, start, finish, p);
 }
@@ -273,10 +274,11 @@ function find(startOpt, sub, s) {
   try {
     while((i + n | 0) <= s_len) {
       if (unsafe_is_sub(sub, 0, s, i, n)) {
-        throw {
-              MEL_EXN_ID: Local_exit,
-              Error: new Error()
-            };
+        throw new Error(Local_exit, {
+                  cause: {
+                    MEL_EXN_ID: Local_exit
+                  }
+                });
       }
       i = i + 1 | 0;
     };
@@ -287,7 +289,9 @@ function find(startOpt, sub, s) {
     if (exn.MEL_EXN_ID === Local_exit) {
       return i;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -298,11 +302,12 @@ function contain_substring(s, sub) {
 function non_overlap_count(sub, s) {
   var sub_len = sub.length;
   if (sub.length === 0) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_string_test.non_overlap_count",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_string_test.non_overlap_count"
+              }
+            });
   }
   var _acc = 0;
   var _off = 0;
@@ -325,10 +330,11 @@ function rfind(sub, s) {
   try {
     while(i >= 0) {
       if (unsafe_is_sub(sub, 0, s, i, n)) {
-        throw {
-              MEL_EXN_ID: Local_exit,
-              Error: new Error()
-            };
+        throw new Error(Local_exit, {
+                  cause: {
+                    MEL_EXN_ID: Local_exit
+                  }
+                });
       }
       i = i - 1 | 0;
     };
@@ -339,7 +345,9 @@ function rfind(sub, s) {
     if (exn.MEL_EXN_ID === Local_exit) {
       return i;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -349,11 +357,12 @@ function tail_from(s, x) {
     return Stdlib__String.sub(s, x, len - x | 0);
   }
   var s$1 = "Ext_string_test.tail_from " + (s + (" : " + String(x)));
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: s$1,
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: s$1
+            }
+          });
 }
 
 function digits_of_str(s, offset, x) {
@@ -568,11 +577,12 @@ function unsafe_no_char_idx(x, ch, _i, last_idx) {
 function no_char(x, ch, i, len) {
   var str_len = x.length;
   if (i < 0 || i >= str_len || len >= str_len) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Ext_string_test.no_char",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Ext_string_test.no_char"
+              }
+            });
   }
   return unsafe_no_char(x, ch, i, len);
 }
diff --git a/jscomp/test/dist/jscomp/test/extensible_variant_test.js b/jscomp/test/dist/jscomp/test/extensible_variant_test.js
index f78aca15ca..d37cd21b4e 100644
--- a/jscomp/test/dist/jscomp/test/extensible_variant_test.js
+++ b/jscomp/test/dist/jscomp/test/extensible_variant_test.js
@@ -24,15 +24,16 @@ function to_int(x) {
   if (x.MEL_EXN_ID === Int$1) {
     return x._2;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/extensible_variant_test.ml",
-          16,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/extensible_variant_test.ml",
+                16,
+                9
+              ]
+            }
+          });
 }
 
 var suites_0 = [
diff --git a/jscomp/test/dist/jscomp/test/flexible_array_test.js b/jscomp/test/dist/jscomp/test/flexible_array_test.js
index cea6ccc9bb..819f90df23 100644
--- a/jscomp/test/dist/jscomp/test/flexible_array_test.js
+++ b/jscomp/test/dist/jscomp/test/flexible_array_test.js
@@ -25,10 +25,11 @@ function sub(_tr, _k) {
       _tr = tr._2;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -65,10 +66,11 @@ function update(tr, k, w) {
             _2: /* Lf */0
           };
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function $$delete(tr, n) {
@@ -93,10 +95,11 @@ function $$delete(tr, n) {
             };
     }
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function loext(tr, w) {
@@ -128,20 +131,22 @@ function lorem(tr) {
     if (!tr._2) {
       return /* Lf */0;
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/flexible_array_test.ml",
-            66,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/flexible_array_test.ml",
+                  66,
+                  9
+                ]
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 var empty = [
@@ -157,11 +162,12 @@ function get(param, i) {
   if (i >= 0 && i < param[1]) {
     return sub(param[0], i + 1 | 0);
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Array.get",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Array.get"
+            }
+          });
 }
 
 function set(param, i, v) {
@@ -172,11 +178,12 @@ function set(param, i, v) {
             k
           ];
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Array.set",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Array.set"
+            }
+          });
 }
 
 function push_front(param, v) {
@@ -194,11 +201,12 @@ function pop_front(param) {
             k - 1 | 0
           ];
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Array.pop_front",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Array.pop_front"
+            }
+          });
 }
 
 function push_back(param, v) {
@@ -217,11 +225,12 @@ function pop_back(param) {
             k - 1 | 0
           ];
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Array.pop_back",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Array.pop_back"
+            }
+          });
 }
 
 function pp(fmt, s) {
@@ -326,15 +335,16 @@ if (!Caml_obj.caml_equal(x, of_array([
             5,
             6
           ]))) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/flexible_array_test.ml",
-          166,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/flexible_array_test.ml",
+                166,
+                4
+              ]
+            }
+          });
 }
 
 var v = Stdlib__Array.init(500, (function (i) {
diff --git a/jscomp/test/dist/jscomp/test/flow_parser_reg_test.js b/jscomp/test/dist/jscomp/test/flow_parser_reg_test.js
index cc74f1d7b7..9e8c8c6731 100644
--- a/jscomp/test/dist/jscomp/test/flow_parser_reg_test.js
+++ b/jscomp/test/dist/jscomp/test/flow_parser_reg_test.js
@@ -2133,10 +2133,11 @@ function eat(f) {
             todo: match.tl
           };
   }
-  throw {
-        MEL_EXN_ID: No_good,
-        Error: new Error()
-      };
+  throw new Error(No_good, {
+            cause: {
+              MEL_EXN_ID: No_good
+            }
+          });
 }
 
 function start(str) {
@@ -2186,10 +2187,11 @@ function parse_hex_symbol(f) {
   var match = f.todo;
   if (match) {
     if (match.hd !== 48) {
-      throw {
-            MEL_EXN_ID: No_good,
-            Error: new Error()
-          };
+      throw new Error(No_good, {
+                cause: {
+                  MEL_EXN_ID: No_good
+                }
+              });
     }
     var match$1 = match.tl;
     if (match$1) {
@@ -2198,22 +2200,25 @@ function parse_hex_symbol(f) {
         return eat(eat(f));
       }
       if (match$2 !== 120) {
-        throw {
-              MEL_EXN_ID: No_good,
-              Error: new Error()
-            };
+        throw new Error(No_good, {
+                  cause: {
+                    MEL_EXN_ID: No_good
+                  }
+                });
       }
       return eat(eat(f));
     }
-    throw {
-          MEL_EXN_ID: No_good,
-          Error: new Error()
-        };
+    throw new Error(No_good, {
+              cause: {
+                MEL_EXN_ID: No_good
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: No_good,
-        Error: new Error()
-      };
+  throw new Error(No_good, {
+            cause: {
+              MEL_EXN_ID: No_good
+            }
+          });
 }
 
 function parse_exponent(f) {
@@ -2225,12 +2230,15 @@ function parse_exponent(f) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Failure) {
-      throw {
-            MEL_EXN_ID: No_good,
-            Error: new Error()
-          };
+      throw new Error(No_good, {
+                cause: {
+                  MEL_EXN_ID: No_good
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return {
           negative: f.negative,
@@ -2276,10 +2284,11 @@ function parse_body(_f) {
         };
         continue ;
       }
-      throw {
-            MEL_EXN_ID: No_good,
-            Error: new Error()
-          };
+      throw new Error(No_good, {
+                cause: {
+                  MEL_EXN_ID: No_good
+                }
+              });
     }
     var ref_char_code;
     if (c >= /* '0' */48 && c <= /* '9' */57) {
@@ -2289,10 +2298,11 @@ function parse_body(_f) {
     } else if (c >= /* 'a' */97 && c <= /* 'f' */102) {
       ref_char_code = 87;
     } else {
-      throw {
-            MEL_EXN_ID: No_good,
-            Error: new Error()
-          };
+      throw new Error(No_good, {
+                cause: {
+                  MEL_EXN_ID: No_good
+                }
+              });
     }
     var value = c - ref_char_code | 0;
     var e = f.decimal_exponent;
@@ -2319,15 +2329,16 @@ function float_of_string(str) {
       try {
         var f = parse_body(parse_hex_symbol(parse_sign(start(str))));
         if (!Caml_obj.caml_equal(f.todo, /* [] */0)) {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "lexer_flow.mll",
-                  546,
-                  4
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "lexer_flow.mll",
+                        546,
+                        4
+                      ]
+                    }
+                  });
         }
         var ret = f.mantissa;
         var decimal_exponent = f.decimal_exponent;
@@ -2342,12 +2353,18 @@ function float_of_string(str) {
       catch (raw_exn){
         var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
         if (exn.MEL_EXN_ID === No_good) {
-          throw e;
+          throw new Error(e.MEL_EXN_ID, {
+                    cause: e
+                  });
         }
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     } else {
-      throw e;
+      throw new Error(e.MEL_EXN_ID, {
+                cause: e
+              });
     }
   }
 }
@@ -2412,15 +2429,16 @@ function unicode_fix_cols(lb) {
 
 function oct_to_int(x) {
   if (x > 55 || x < 48) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "lexer_flow.mll",
-            604,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "lexer_flow.mll",
+                  604,
+                  11
+                ]
+              }
+            });
   }
   return x - /* '0' */48 | 0;
 }
@@ -2439,15 +2457,16 @@ function hexa_to_int(x) {
   } else if (!(x > 57 || x < 48)) {
     return x - /* '0' */48 | 0;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "lexer_flow.mll",
-          610,
-          11
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "lexer_flow.mll",
+                610,
+                11
+              ]
+            }
+          });
 }
 
 function utf16to8(code) {
@@ -3103,7 +3122,9 @@ function token(env, lexbuf) {
                       /* T_IDENTIFIER */0
                     ];
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
       case 23 :
           return [
@@ -5155,7 +5176,9 @@ function type_token(env, lexbuf) {
                 }
               ];
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
           return illegal_number(match$4[0], lexbuf, w$3, match$4[1]);
@@ -5181,7 +5204,9 @@ function type_token(env, lexbuf) {
                       }
                     ];
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
       case 15 :
           var neg$8 = Stdlib__Lexing.sub_lexeme(lexbuf, lexbuf.lex_start_pos, Caml_array.get(lexbuf.lex_mem, 0));
@@ -5224,7 +5249,9 @@ function type_token(env, lexbuf) {
                       /* T_IDENTIFIER */0
                     ];
             }
-            throw exn$2;
+            throw new Error(exn$2.MEL_EXN_ID, {
+                      cause: exn$2
+                    });
           }
       case 22 :
           return [
@@ -5500,17 +5527,19 @@ function bal(l, v, r) {
       if (lr) {
         return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -5530,17 +5559,19 @@ function bal(l, v, r) {
     if (rl) {
       return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add(x, t) {
@@ -5817,15 +5848,16 @@ function record_export(env, param) {
 function lookahead(iOpt, env) {
   var i = iOpt !== undefined ? iOpt : 0;
   if (i >= 2) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "parser_env.ml",
-            288,
-            2
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "parser_env.ml",
+                  288,
+                  2
+                ]
+              }
+            });
   }
   var t = env.lookahead.contents;
   lex_until(t, i);
@@ -5833,11 +5865,12 @@ function lookahead(iOpt, env) {
   if (match !== undefined) {
     return match[1];
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "Lookahead.peek failed",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "Lookahead.peek failed"
+            }
+          });
 }
 
 function with_strict(in_strict_mode, env) {
@@ -5998,11 +6031,12 @@ function lex_env(iOpt, env) {
   if (match !== undefined) {
     return match[0];
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "Lookahead.peek failed",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "Lookahead.peek failed"
+            }
+          });
 }
 
 function is_line_terminator(env) {
@@ -6202,11 +6236,12 @@ function pop_lex_mode(env) {
   if (match) {
     new_stack = match.tl;
   } else {
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "Popping lex mode from empty stack",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "Popping lex mode from empty stack"
+              }
+            });
   }
   env.lex_mode_stack.contents = new_stack;
   env.lookahead.contents = create$1(env.lex_env.contents, Stdlib__List.hd(env.lex_mode_stack.contents));
@@ -6220,18 +6255,20 @@ function double_pop_lex_mode(env) {
     if (match$1) {
       new_stack = match$1.tl;
     } else {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "Popping lex mode from empty stack",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "Popping lex mode from empty stack"
+                }
+              });
     }
   } else {
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "Popping lex mode from empty stack",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "Popping lex mode from empty stack"
+              }
+            });
   }
   env.lex_mode_stack.contents = new_stack;
   env.lookahead.contents = create$1(env.lex_env.contents, Stdlib__List.hd(env.lex_mode_stack.contents));
@@ -6335,7 +6372,9 @@ function to_parse(env, parse) {
       env.lookahead.contents = create$1(env.lex_env.contents, Stdlib__List.hd(env.lex_mode_stack.contents));
       return /* FailedToParse */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -6395,17 +6434,19 @@ function bal$1(l, v, r) {
       if (lr) {
         return create$2(create$2(ll, lv, lr.l), lr.v, create$2(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -6425,17 +6466,19 @@ function bal$1(l, v, r) {
     if (rl) {
       return create$2(create$2(l, v, rl.l), rl.v, create$2(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$1(x, t) {
@@ -6524,17 +6567,19 @@ function bal$2(l, x, d, r) {
       if (lr) {
         return create$3(create$3(ll, lv, ld, lr.l), lr.v, lr.d, create$3(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -6556,17 +6601,19 @@ function bal$2(l, x, d, r) {
     if (rl) {
       return create$3(create$3(l, x, d, rl.l), rl.v, rl.d, create$3(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add$2(x, data, m) {
@@ -6624,10 +6671,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -6677,17 +6725,19 @@ function bal$3(l, v, r) {
       if (lr) {
         return create$4(create$4(ll, lv, lr.l), lr.v, create$4(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -6707,17 +6757,19 @@ function bal$3(l, v, r) {
     if (rl) {
       return create$4(create$4(l, v, rl.l), rl.v, create$4(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$3(x, t) {
@@ -7333,30 +7385,32 @@ function rev_nonempty_acc(acc) {
   if (acc) {
     end_loc = acc.hd[0];
   } else {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "parser_flow.ml",
-            127,
-            13
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "parser_flow.ml",
+                  127,
+                  13
+                ]
+              }
+            });
   }
   var acc$1 = Stdlib__List.rev(acc);
   var start_loc;
   if (acc$1) {
     start_loc = acc$1.hd[0];
   } else {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "parser_flow.ml",
-            131,
-            13
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "parser_flow.ml",
+                  131,
+                  13
+                ]
+              }
+            });
   }
   return [
           btwn(start_loc, end_loc),
@@ -7960,15 +8014,16 @@ function annotation(env) {
   if (loc !== undefined) {
     end_loc = loc;
   } else {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "parser_flow.ml",
-            121,
-            16
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "parser_flow.ml",
+                  121,
+                  16
+                ]
+              }
+            });
   }
   return [
           btwn(start_loc, end_loc),
@@ -9027,7 +9082,9 @@ function number(env, number_type) {
               error$1(env, /* WindowsFloatOfString */59);
               value$1 = 789.0;
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
           break;
@@ -9160,15 +9217,16 @@ function primary$1(env) {
           var match$4 = Curry._2(Parser_env_Peek.token, undefined, env);
           var match$5;
           if (typeof match$4 === "number") {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "parser_flow.ml",
-                    1699,
-                    15
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "parser_flow.ml",
+                          1699,
+                          15
+                        ]
+                      }
+                    });
           }
           if (match$4.TAG === /* T_REGEXP */3) {
             var match$6 = match$4._0;
@@ -9180,15 +9238,16 @@ function primary$1(env) {
               match$6[2]
             ];
           } else {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "parser_flow.ml",
-                    1699,
-                    15
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "parser_flow.ml",
+                          1699,
+                          15
+                        ]
+                      }
+                    });
           }
           var raw_flags = match$5[2];
           pop_lex_mode(env);
@@ -9507,10 +9566,11 @@ function assignment_but_not_arrow_function(env) {
 }
 
 function error_callback(param, param$1) {
-  throw {
-        MEL_EXN_ID: Parser_env_Try.Rollback,
-        Error: new Error()
-      };
+  throw new Error(Parser_env_Try.Rollback, {
+            cause: {
+              MEL_EXN_ID: Parser_env_Try.Rollback
+            }
+          });
 }
 
 function try_assignment_but_not_arrow_function(env) {
@@ -9520,27 +9580,30 @@ function try_assignment_but_not_arrow_function(env) {
   if (typeof match === "number") {
     if (match !== 10) {
       if (match === 77) {
-        throw {
-              MEL_EXN_ID: Parser_env_Try.Rollback,
-              Error: new Error()
-            };
+        throw new Error(Parser_env_Try.Rollback, {
+                  cause: {
+                    MEL_EXN_ID: Parser_env_Try.Rollback
+                  }
+                });
       }
       
     } else {
-      throw {
-            MEL_EXN_ID: Parser_env_Try.Rollback,
-            Error: new Error()
-          };
+      throw new Error(Parser_env_Try.Rollback, {
+                cause: {
+                  MEL_EXN_ID: Parser_env_Try.Rollback
+                }
+              });
     }
   }
   if (!Curry._2(Parser_env_Peek.is_identifier, undefined, env$1)) {
     return ret;
   }
   if (Curry._2(Parser_env_Peek.value, undefined, env$1) === "checks") {
-    throw {
-          MEL_EXN_ID: Parser_env_Try.Rollback,
-          Error: new Error()
-        };
+    throw new Error(Parser_env_Try.Rollback, {
+              cause: {
+                MEL_EXN_ID: Parser_env_Try.Rollback
+              }
+            });
   }
   var match$1 = ret[1];
   if (typeof match$1 === "number") {
@@ -9553,10 +9616,11 @@ function try_assignment_but_not_arrow_function(env) {
     return ret;
   }
   if (!Curry._1(Parser_env_Peek.is_line_terminator, env$1)) {
-    throw {
-          MEL_EXN_ID: Parser_env_Try.Rollback,
-          Error: new Error()
-        };
+    throw new Error(Parser_env_Try.Rollback, {
+              cause: {
+                MEL_EXN_ID: Parser_env_Try.Rollback
+              }
+            });
   }
   return ret;
 }
@@ -10095,15 +10159,16 @@ function template_parts(env, _quasis, _expressions) {
       var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
       var match$2;
       if (typeof match$1 === "number") {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "parser_flow.ml",
-                1602,
-                19
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "parser_flow.ml",
+                      1602,
+                      19
+                    ]
+                  }
+                });
       }
       if (match$1.TAG === /* T_TEMPLATE_PART */2) {
         var match$3 = match$1._0;
@@ -10122,15 +10187,16 @@ function template_parts(env, _quasis, _expressions) {
           tail
         ];
       } else {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "parser_flow.ml",
-                1602,
-                19
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "parser_flow.ml",
+                      1602,
+                      19
+                    ]
+                  }
+                });
       }
       var loc = match$2[0];
       pop_lex_mode(env);
@@ -10306,23 +10372,26 @@ function error_callback$1(param) {
         if (param === 47) {
           return ;
         }
-        throw {
-              MEL_EXN_ID: Parser_env_Try.Rollback,
-              Error: new Error()
-            };
+        throw new Error(Parser_env_Try.Rollback, {
+                  cause: {
+                    MEL_EXN_ID: Parser_env_Try.Rollback
+                  }
+                });
       }
       if (param > 43 || param < 29) {
         return ;
       }
-      throw {
-            MEL_EXN_ID: Parser_env_Try.Rollback,
-            Error: new Error()
-          };
+      throw new Error(Parser_env_Try.Rollback, {
+                cause: {
+                  MEL_EXN_ID: Parser_env_Try.Rollback
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: Parser_env_Try.Rollback,
-          Error: new Error()
-        };
+    throw new Error(Parser_env_Try.Rollback, {
+              cause: {
+                MEL_EXN_ID: Parser_env_Try.Rollback
+              }
+            });
   };
 }
 
@@ -10543,15 +10612,16 @@ function _method(env, kind) {
   var params;
   switch (kind) {
     case /* Init */0 :
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "parser_flow.ml",
-                1954,
-                16
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "parser_flow.ml",
+                      1954,
+                      16
+                    ]
+                  }
+                });
     case /* Get */1 :
         params = /* [] */0;
         break;
@@ -10899,11 +10969,12 @@ function check_property(env, prop_map, prop) {
                   key = Stdlib.string_of_float(s._0);
                   break;
               case /* RegExp */3 :
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "RegExp cannot be property key",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "RegExp cannot be property key"
+                            }
+                          });
               
             }
           }
@@ -10912,15 +10983,16 @@ function check_property(env, prop_map, prop) {
           key = match$1._0[1].name;
           break;
       case /* Computed */2 :
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "parser_flow.ml",
-                  2103,
-                  30
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "parser_flow.ml",
+                        2103,
+                        30
+                      ]
+                    }
+                  });
       
     }
     var prev_kinds;
@@ -10932,7 +11004,9 @@ function check_property(env, prop_map, prop) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         prev_kinds = /* Empty */0;
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
     var match$2 = prop$1.kind;
@@ -11783,15 +11857,16 @@ function declare_export_declaration(allow_export_typeOpt, env) {
         }
         switch (exit$2) {
           case 3 :
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "parser_flow.ml",
-                      3480,
-                      17
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "parser_flow.ml",
+                            3480,
+                            17
+                          ]
+                        }
+                      });
           case 4 :
               if (typeof token$5 === "number") {
                 if (token$5 !== 25) {
@@ -12419,11 +12494,12 @@ function fold(acc) {
                   tl: acc
                 };
       case /* Expression */4 :
-          throw {
-                MEL_EXN_ID: "Failure",
-                _1: "Parser error: No such thing as an expression pattern!",
-                Error: new Error()
-              };
+          throw new Error("Failure", {
+                    cause: {
+                      MEL_EXN_ID: "Failure",
+                      _1: "Parser error: No such thing as an expression pattern!"
+                    }
+                  });
       
     }
   };
@@ -14006,15 +14082,16 @@ function statement(env) {
                               _0: init._0
                             });
                       } else {
-                        throw {
-                              MEL_EXN_ID: "Assert_failure",
-                              _1: [
-                                "parser_flow.ml",
-                                2573,
-                                22
-                              ],
-                              Error: new Error()
-                            };
+                        throw new Error("Assert_failure", {
+                                  cause: {
+                                    MEL_EXN_ID: "Assert_failure",
+                                    _1: [
+                                      "parser_flow.ml",
+                                      2573,
+                                      22
+                                    ]
+                                  }
+                                });
                       }
                       token$4(env, /* T_OF */60);
                       var right = Curry._1(Parse.assignment, env);
@@ -14045,15 +14122,16 @@ function statement(env) {
                             _0: init._0
                           });
                     } else {
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "parser_flow.ml",
-                              2556,
-                              22
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "parser_flow.ml",
+                                    2556,
+                                    22
+                                  ]
+                                }
+                              });
                     }
                     token$4(env, /* T_IN */15);
                     var right$1 = Curry._1(Parse.expression, env);
@@ -14309,11 +14387,12 @@ function module_item(env) {
                       var $$interface$1 = $$interface(env$1);
                       var match$2 = $$interface$1[1];
                       if (typeof match$2 === "number") {
-                        throw {
-                              MEL_EXN_ID: "Failure",
-                              _1: "Internal Flow Error! Parsed `export interface` into something other than an interface declaration!",
-                              Error: new Error()
-                            };
+                        throw new Error("Failure", {
+                                  cause: {
+                                    MEL_EXN_ID: "Failure",
+                                    _1: "Internal Flow Error! Parsed `export interface` into something other than an interface declaration!"
+                                  }
+                                });
                       }
                       if (match$2.TAG === /* InterfaceDeclaration */21) {
                         record_export(env$1, [
@@ -14321,11 +14400,12 @@ function module_item(env) {
                               extract_ident_name(match$2._0.id)
                             ]);
                       } else {
-                        throw {
-                              MEL_EXN_ID: "Failure",
-                              _1: "Internal Flow Error! Parsed `export interface` into something other than an interface declaration!",
-                              Error: new Error()
-                            };
+                        throw new Error("Failure", {
+                                  cause: {
+                                    MEL_EXN_ID: "Failure",
+                                    _1: "Internal Flow Error! Parsed `export interface` into something other than an interface declaration!"
+                                  }
+                                });
                       }
                       var end_loc = $$interface$1[0];
                       return [
@@ -14352,11 +14432,12 @@ function module_item(env) {
                         var type_alias$1 = type_alias(env$1);
                         var match$3 = type_alias$1[1];
                         if (typeof match$3 === "number") {
-                          throw {
-                                MEL_EXN_ID: "Failure",
-                                _1: "Internal Flow Error! Parsed `export type` into something other than a type alias!",
-                                Error: new Error()
-                              };
+                          throw new Error("Failure", {
+                                    cause: {
+                                      MEL_EXN_ID: "Failure",
+                                      _1: "Internal Flow Error! Parsed `export type` into something other than a type alias!"
+                                    }
+                                  });
                         }
                         if (match$3.TAG === /* TypeAlias */7) {
                           record_export(env$1, [
@@ -14364,11 +14445,12 @@ function module_item(env) {
                                 extract_ident_name(match$3._0.id)
                               ]);
                         } else {
-                          throw {
-                                MEL_EXN_ID: "Failure",
-                                _1: "Internal Flow Error! Parsed `export type` into something other than a type alias!",
-                                Error: new Error()
-                              };
+                          throw new Error("Failure", {
+                                    cause: {
+                                      MEL_EXN_ID: "Failure",
+                                      _1: "Internal Flow Error! Parsed `export type` into something other than a type alias!"
+                                    }
+                                  });
                         }
                         var end_loc$1 = type_alias$1[0];
                         return [
@@ -14565,11 +14647,12 @@ function module_item(env) {
               var loc$4 = stmt[0];
               var names;
               if (typeof match$8 === "number") {
-                throw {
-                      MEL_EXN_ID: "Failure",
-                      _1: "Internal Flow Error! Unexpected export statement declaration!",
-                      Error: new Error()
-                    };
+                throw new Error("Failure", {
+                          cause: {
+                            MEL_EXN_ID: "Failure",
+                            _1: "Internal Flow Error! Unexpected export statement declaration!"
+                          }
+                        });
               }
               switch (match$8.TAG | 0) {
                 case /* FunctionDeclaration */18 :
@@ -14619,11 +14702,12 @@ function module_item(env) {
                     }
                     break;
                 default:
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "Internal Flow Error! Unexpected export statement declaration!",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "Internal Flow Error! Unexpected export statement declaration!"
+                            }
+                          });
               }
               Stdlib__List.iter((function (param) {
                       return record_export(env$1, param);
@@ -15047,11 +15131,12 @@ function directives(env, term_fn, item_fn) {
             }
           }
           var s = "Nooo: " + (token_to_string(token) + "\n");
-          throw {
-                MEL_EXN_ID: "Failure",
-                _1: s,
-                Error: new Error()
-              };
+          throw new Error("Failure", {
+                    cause: {
+                      MEL_EXN_ID: "Failure",
+                      _1: s
+                    }
+                  });
         }), Stdlib__List.rev(match[1]));
   return [
           env$1,
@@ -15414,11 +15499,12 @@ function program$1(failOpt, token_sinkOpt, parse_optionsOpt, content) {
   var ast = Curry._1(parser, env);
   var error_list = filter_duplicate_errors(env.errors.contents);
   if (fail && Caml_obj.caml_notequal(error_list, /* [] */0)) {
-    throw {
-          MEL_EXN_ID: $$Error,
-          _1: error_list,
-          Error: new Error()
-        };
+    throw new Error($$Error, {
+              cause: {
+                MEL_EXN_ID: $$Error,
+                _1: error_list
+              }
+            });
   }
   return [
           ast,
@@ -15794,11 +15880,12 @@ function parse(content, options) {
                   operator = "delete";
                   break;
               case /* Await */7 :
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "matched above",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "matched above"
+                            }
+                          });
               
             }
             return node("UnaryExpression", loc, [
@@ -17761,11 +17848,12 @@ function parse(content, options) {
             key = identifier(lit._0);
             break;
         case /* Computed */2 :
-            throw {
-                  MEL_EXN_ID: "Failure",
-                  _1: "There should not be computed object type property keys",
-                  Error: new Error()
-                };
+            throw new Error("Failure", {
+                      cause: {
+                        MEL_EXN_ID: "Failure",
+                        _1: "There should not be computed object type property keys"
+                      }
+                    });
         
       }
       return node("ObjectTypeProperty", param[0], [
@@ -17846,7 +17934,9 @@ function parse(content, options) {
       throw(e);
       return {};
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -17885,15 +17975,16 @@ if (f !== undefined) {
         2842
       ], v.range);
 } else {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "runParser.ml",
-          15,
-          12
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "runParser.ml",
+                15,
+                12
+              ]
+            }
+          });
 }
 
 Mt.from_pair_suites("Flow_parser_reg_test", suites.contents);
diff --git a/jscomp/test/dist/jscomp/test/format_regression.js b/jscomp/test/dist/jscomp/test/format_regression.js
index 7b7ac73916..73d7f893b9 100644
--- a/jscomp/test/dist/jscomp/test/format_regression.js
+++ b/jscomp/test/dist/jscomp/test/format_regression.js
@@ -4,51 +4,55 @@
 var Curry = require("melange.js/curry.js");
 
 function peek_queue(param) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/format_regression.ml",
-          10,
-          19
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/format_regression.ml",
+                10,
+                19
+              ]
+            }
+          });
 }
 
 function int_of_size(param) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/format_regression.ml",
-          11,
-          20
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/format_regression.ml",
+                11,
+                20
+              ]
+            }
+          });
 }
 
 function take_queue(param) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/format_regression.ml",
-          12,
-          19
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/format_regression.ml",
+                12,
+                19
+              ]
+            }
+          });
 }
 
 function format_pp_token(param, param$1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/format_regression.ml",
-          13,
-          26
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/format_regression.ml",
+                13,
+                26
+              ]
+            }
+          });
 }
 
 function advance_loop(state) {
diff --git a/jscomp/test/dist/jscomp/test/fun_pattern_match.js b/jscomp/test/dist/jscomp/test/fun_pattern_match.js
index d2aecb0eb4..d85b32bb2f 100644
--- a/jscomp/test/dist/jscomp/test/fun_pattern_match.js
+++ b/jscomp/test/dist/jscomp/test/fun_pattern_match.js
@@ -17,26 +17,28 @@ function f3(param) {
   return function (param) {
     var rhs = param.rank;
     if (typeof lhs === "number") {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/fun_pattern_match.ml",
-              41,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/fun_pattern_match.ml",
+                    41,
+                    9
+                  ]
+                }
+              });
     }
     if (typeof rhs === "number") {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/fun_pattern_match.ml",
-              41,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/fun_pattern_match.ml",
+                    41,
+                    9
+                  ]
+                }
+              });
     }
     return Caml.caml_int_compare(lhs._0, rhs._0);
   };
@@ -47,26 +49,28 @@ function f4(param) {
   return function (param) {
     var rhs = param.rank;
     if (typeof lhs === "number") {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/fun_pattern_match.ml",
-              49,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/fun_pattern_match.ml",
+                    49,
+                    9
+                  ]
+                }
+              });
     }
     if (typeof rhs === "number") {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/fun_pattern_match.ml",
-              49,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/fun_pattern_match.ml",
+                    49,
+                    9
+                  ]
+                }
+              });
     }
     return Caml.caml_int_compare(lhs._0, rhs._0);
   };
diff --git a/jscomp/test/dist/jscomp/test/gpr_1150.js b/jscomp/test/dist/jscomp/test/gpr_1150.js
index aa8442b1cf..9aa3825cd7 100644
--- a/jscomp/test/dist/jscomp/test/gpr_1150.js
+++ b/jscomp/test/dist/jscomp/test/gpr_1150.js
@@ -215,15 +215,16 @@ function f(children) {
           ];
   }
   if (children$15.tl) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/gpr_1150.ml",
-            56,
-            34
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/gpr_1150.ml",
+                  56,
+                  34
+                ]
+              }
+            });
   }
   return [
           a0,
diff --git a/jscomp/test/dist/jscomp/test/gpr_1245_test.js b/jscomp/test/dist/jscomp/test/gpr_1245_test.js
index e26354cff2..17e3fac5ff 100644
--- a/jscomp/test/dist/jscomp/test/gpr_1245_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_1245_test.js
@@ -48,7 +48,9 @@ function a1(f) {
     if (exn.MEL_EXN_ID === E) {
       return 1;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/gpr_1698_test.js b/jscomp/test/dist/jscomp/test/gpr_1698_test.js
index 0d2fad1329..4f73d3ffe1 100644
--- a/jscomp/test/dist/jscomp/test/gpr_1698_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_1698_test.js
@@ -49,15 +49,16 @@ function compare(context, state, _a, _b) {
                 exit$2 = 4;
                 break;
             case /* Frac */4 :
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/gpr_1698_test.ml",
-                        45,
-                        10
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/gpr_1698_test.ml",
+                              45,
+                              10
+                            ]
+                          }
+                        });
             case /* Pow */3 :
             case /* Gcd */5 :
                 exit = 1;
@@ -75,15 +76,16 @@ function compare(context, state, _a, _b) {
       case /* Frac */4 :
           switch (b.TAG | 0) {
             case /* Val */0 :
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/gpr_1698_test.ml",
-                        45,
-                        10
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/gpr_1698_test.ml",
+                              45,
+                              10
+                            ]
+                          }
+                        });
             case /* Neg */1 :
                 exit$3 = 5;
                 break;
diff --git a/jscomp/test/dist/jscomp/test/gpr_1701_test.js b/jscomp/test/dist/jscomp/test/gpr_1701_test.js
index 43228a2b68..6cf94183b3 100644
--- a/jscomp/test/dist/jscomp/test/gpr_1701_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_1701_test.js
@@ -10,10 +10,11 @@ var Foo = /* @__PURE__ */Caml_exceptions.create("Gpr_1701_test.Foo");
 
 function test(n) {
   if (n === 0) {
-    throw {
-          MEL_EXN_ID: Foo,
-          Error: new Error()
-        };
+    throw new Error(Foo, {
+              cause: {
+                MEL_EXN_ID: Foo
+              }
+            });
   }
   try {
     return test(n - 1 | 0);
@@ -23,7 +24,9 @@ function test(n) {
     if (exn.MEL_EXN_ID === Foo) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -42,7 +45,9 @@ function read_lines(inc) {
       if (exn.MEL_EXN_ID === Stdlib.End_of_file) {
         l = undefined;
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
     if (l === undefined) {
@@ -69,7 +74,9 @@ function read_lines2(inc) {
       if (exn.MEL_EXN_ID === Stdlib.End_of_file) {
         return Stdlib__List.rev(acc);
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
     _acc = {
       hd: l,
@@ -93,7 +100,9 @@ function read_lines3(inc) {
       if (exn.MEL_EXN_ID === Stdlib.End_of_file) {
         return Stdlib__List.rev(acc);
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   return loop(/* [] */0);
diff --git a/jscomp/test/dist/jscomp/test/gpr_2316_test.js b/jscomp/test/dist/jscomp/test/gpr_2316_test.js
index f3b1cf0c63..33ce4e4b9c 100644
--- a/jscomp/test/dist/jscomp/test/gpr_2316_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_2316_test.js
@@ -33,18 +33,21 @@ function eq(loc, x, y) {
 var y;
 
 try {
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "boo",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "boo"
+            }
+          });
 }
 catch (raw_exn){
   var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
   if (exn.MEL_EXN_ID === Stdlib.Failure) {
     y = exn._1;
   } else {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -53,18 +56,21 @@ var x;
 var exit = 0;
 
 try {
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "boo",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "boo"
+            }
+          });
 }
 catch (raw_exn$1){
   var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
   if (exn$1.MEL_EXN_ID === Stdlib.Failure) {
     x = exn$1._1;
   } else {
-    throw exn$1;
+    throw new Error(exn$1.MEL_EXN_ID, {
+              cause: exn$1
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/gpr_2474.js b/jscomp/test/dist/jscomp/test/gpr_2474.js
index ef304beb83..b64fa239c4 100644
--- a/jscomp/test/dist/jscomp/test/gpr_2474.js
+++ b/jscomp/test/dist/jscomp/test/gpr_2474.js
@@ -2,15 +2,16 @@
 'use strict';
 
 
-throw {
-      MEL_EXN_ID: "Match_failure",
-      _1: [
-        "gpr_2474.ml",
-        6,
-        4
-      ],
-      Error: new Error()
-    };
+throw new Error("Match_failure", {
+          cause: {
+            MEL_EXN_ID: "Match_failure",
+            _1: [
+              "gpr_2474.ml",
+              6,
+              4
+            ]
+          }
+        });
 
 exports.coordinates = coordinates;
 /*  Not a pure module */
diff --git a/jscomp/test/dist/jscomp/test/gpr_2682_test.js b/jscomp/test/dist/jscomp/test/gpr_2682_test.js
index 9ba777bdbe..c87ea3a28d 100644
--- a/jscomp/test/dist/jscomp/test/gpr_2682_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_2682_test.js
@@ -49,15 +49,16 @@ var f3 = (()=>true
 var bbbb = f3();
 
 if (!bbbb) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/gpr_2682_test.ml",
-          59,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/gpr_2682_test.ml",
+                59,
+                2
+              ]
+            }
+          });
 }
 
 exports.sum = sum;
diff --git a/jscomp/test/dist/jscomp/test/gpr_3595_test.js b/jscomp/test/dist/jscomp/test/gpr_3595_test.js
index 4205e18bfa..95d294d256 100644
--- a/jscomp/test/dist/jscomp/test/gpr_3595_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_3595_test.js
@@ -18,15 +18,16 @@ function eq(loc, x, y) {
 var match = [1];
 
 if (match.length !== 1) {
-  throw {
-        MEL_EXN_ID: "Match_failure",
-        _1: [
-          "gpr_3595_test.ml",
-          9,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Match_failure", {
+            cause: {
+              MEL_EXN_ID: "Match_failure",
+              _1: [
+                "gpr_3595_test.ml",
+                9,
+                4
+              ]
+            }
+          });
 }
 
 var a = match[0];
diff --git a/jscomp/test/dist/jscomp/test/gpr_3877_test.js b/jscomp/test/dist/jscomp/test/gpr_3877_test.js
index 0aa308a67b..854da596e5 100644
--- a/jscomp/test/dist/jscomp/test/gpr_3877_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_3877_test.js
@@ -21,27 +21,29 @@ var a = "good response";
 var b = "bad response";
 
 if (a !== "good response") {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/gpr_3877_test.ml",
-          14,
-          3
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/gpr_3877_test.ml",
+                14,
+                3
+              ]
+            }
+          });
 }
 
 if (b !== "bad response") {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/gpr_3877_test.ml",
-          15,
-          3
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/gpr_3877_test.ml",
+                15,
+                3
+              ]
+            }
+          });
 }
 
 exports.test = test;
diff --git a/jscomp/test/dist/jscomp/test/gpr_3980_test.js b/jscomp/test/dist/jscomp/test/gpr_3980_test.js
index 8050e5ea3e..540b4ccf1f 100644
--- a/jscomp/test/dist/jscomp/test/gpr_3980_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_3980_test.js
@@ -7,42 +7,45 @@ var match = 1;
 
 if (match !== undefined) {
   if (match !== 1) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/gpr_3980_test.ml",
-            16,
-            10
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/gpr_3980_test.ml",
+                  16,
+                  10
+                ]
+              }
+            });
   }
   var match$1 = 1;
   if (match$1 !== 1) {
     if (match$1 !== 2) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/gpr_3980_test.ml",
-              14,
-              12
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/gpr_3980_test.ml",
+                    14,
+                    12
+                  ]
+                }
+              });
     }
     Js__Js_math.floor_int(1);
   }
   
 } else {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/gpr_3980_test.ml",
-          16,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/gpr_3980_test.ml",
+                16,
+                10
+              ]
+            }
+          });
 }
 
 /*  Not a pure module */
diff --git a/jscomp/test/dist/jscomp/test/gpr_405_test.js b/jscomp/test/dist/jscomp/test/gpr_405_test.js
index 8422cb729d..768bebea81 100644
--- a/jscomp/test/dist/jscomp/test/gpr_405_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_405_test.js
@@ -22,7 +22,9 @@ function Make(funarg) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         return false;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   var min_cutset = function (gr, first_node) {
@@ -38,26 +40,28 @@ function Make(funarg) {
     };
     var step2 = function (top, rest_of_stack) {
       if (find_default(already_processed, top)) {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/gpr_405_test.ml",
-                43,
-                6
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/gpr_405_test.ml",
+                      43,
+                      6
+                    ]
+                  }
+                });
       }
       if (find_default(on_the_stack, top)) {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/gpr_405_test.ml",
-                44,
-                6
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/gpr_405_test.ml",
+                      44,
+                      6
+                    ]
+                  }
+                });
       }
       Curry._3(H.add, on_the_stack, top, true);
       Curry._3(H.add, n_labels, top, counter.contents);
@@ -95,11 +99,12 @@ function Make(funarg) {
           Curry._3(H.add, l_labels, top$1, 0);
         }
         if (Curry._2(H.find, l_labels, top$1) > Curry._2(H.find, n_labels, top$1)) {
-          throw {
-                MEL_EXN_ID: Stdlib.Invalid_argument,
-                _1: "Graph.Mincut: graph not reducible",
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Invalid_argument, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Invalid_argument,
+                      _1: "Graph.Mincut: graph not reducible"
+                    }
+                  });
         }
         if (!rest_of_stack$1) {
           return cut_set.contents;
diff --git a/jscomp/test/dist/jscomp/test/gpr_4632.js b/jscomp/test/dist/jscomp/test/gpr_4632.js
index 9c9b6fdcd0..9640deb3b1 100644
--- a/jscomp/test/dist/jscomp/test/gpr_4632.js
+++ b/jscomp/test/dist/jscomp/test/gpr_4632.js
@@ -21,15 +21,16 @@ var T0 = {
   tail: T0_tail
 };
 
-throw {
-      MEL_EXN_ID: "Match_failure",
-      _1: [
-        "gpr_4632.ml",
-        12,
-        6
-      ],
-      Error: new Error()
-    };
+throw new Error("Match_failure", {
+          cause: {
+            MEL_EXN_ID: "Match_failure",
+            _1: [
+              "gpr_4632.ml",
+              12,
+              6
+            ]
+          }
+        });
 
 exports.T0 = T0;
 exports.T1 = T1;
diff --git a/jscomp/test/dist/jscomp/test/gpr_858_unit2_test.js b/jscomp/test/dist/jscomp/test/gpr_858_unit2_test.js
index bff7f2eb66..20f8a94400 100644
--- a/jscomp/test/dist/jscomp/test/gpr_858_unit2_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_858_unit2_test.js
@@ -23,15 +23,16 @@ for(var i = 1; i <= 2; ++i){
     if (i === n) {
       return ;
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/gpr_858_unit2_test.ml",
-            6,
-            13
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/gpr_858_unit2_test.ml",
+                  6,
+                  13
+                ]
+              }
+            });
   }
   }(i));
   f(0, i);
diff --git a/jscomp/test/dist/jscomp/test/gpr_974_test.js b/jscomp/test/dist/jscomp/test/gpr_974_test.js
index 08bff99985..86c0253a6e 100644
--- a/jscomp/test/dist/jscomp/test/gpr_974_test.js
+++ b/jscomp/test/dist/jscomp/test/gpr_974_test.js
@@ -5,39 +5,42 @@ var Caml_obj = require("melange.js/caml_obj.js");
 var Caml_option = require("melange.js/caml_option.js");
 
 if (!Caml_obj.caml_equal(Caml_option.nullable_to_opt(""), "")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/gpr_974_test.ml",
-          3,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/gpr_974_test.ml",
+                3,
+                4
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Caml_option.undefined_to_opt(""), "")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/gpr_974_test.ml",
-          4,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/gpr_974_test.ml",
+                4,
+                4
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(Caml_option.null_to_opt(""), "")) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/gpr_974_test.ml",
-          5,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/gpr_974_test.ml",
+                5,
+                4
+              ]
+            }
+          });
 }
 
 /*  Not a pure module */
diff --git a/jscomp/test/dist/jscomp/test/imm_map_bench.js b/jscomp/test/dist/jscomp/test/imm_map_bench.js
index 71451ee5bb..dc22f51037 100644
--- a/jscomp/test/dist/jscomp/test/imm_map_bench.js
+++ b/jscomp/test/dist/jscomp/test/imm_map_bench.js
@@ -20,7 +20,9 @@ function should(b) {
   if (b) {
     return ;
   }
-  throw new Error("impossible");
+  throw new Error(new Error("impossible").MEL_EXN_ID, {
+            cause: new Error("impossible")
+          });
 }
 
 var shuffledDataAdd = Belt__Belt_Array.makeByAndShuffle(1000001, (function (i) {
diff --git a/jscomp/test/dist/jscomp/test/inline_map2_test.js b/jscomp/test/dist/jscomp/test/inline_map2_test.js
index cf5cfc3452..59d8f65a84 100644
--- a/jscomp/test/dist/jscomp/test/inline_map2_test.js
+++ b/jscomp/test/dist/jscomp/test/inline_map2_test.js
@@ -51,17 +51,19 @@ function Make(Ord) {
         if (lr) {
           return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
         }
-        throw {
-              MEL_EXN_ID: "Invalid_argument",
-              _1: "Map.bal",
-              Error: new Error()
-            };
+        throw new Error("Invalid_argument", {
+                  cause: {
+                    MEL_EXN_ID: "Invalid_argument",
+                    _1: "Map.bal"
+                  }
+                });
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
     if (hr <= (hl + 2 | 0)) {
       return /* Node */{
@@ -83,17 +85,19 @@ function Make(Ord) {
       if (rl) {
         return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
-    }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
+    }
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   };
   var is_empty = function (param) {
     if (param) {
@@ -142,10 +146,11 @@ function Make(Ord) {
         _param = c < 0 ? param._0 : param._3;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     };
   };
   var mem = function (x, _param) {
@@ -176,10 +181,11 @@ function Make(Ord) {
         _param = l;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     };
   };
   var max_binding = function (_param) {
@@ -195,10 +201,11 @@ function Make(Ord) {
         _param = param._3;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     };
   };
   var remove_min_binding = function (param) {
@@ -210,11 +217,12 @@ function Make(Ord) {
         return param._3;
       }
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.remove_min_elt",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.remove_min_elt"
+              }
+            });
   };
   var remove = function (x, param) {
     if (!param) {
@@ -426,15 +434,16 @@ function Make(Ord) {
       var match$1 = split(v2, s1);
       return concat_or_join(merge(f, match$1[0], s2._0), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2._2)), merge(f, match$1[2], s2._3));
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/inline_map2_test.ml",
-            270,
-            10
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/inline_map2_test.ml",
+                  270,
+                  10
+                ]
+              }
+            });
   };
   var filter = function (p, param) {
     if (!param) {
@@ -664,17 +673,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
-    }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
+    }
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -696,17 +707,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function is_empty(param) {
@@ -758,10 +771,11 @@ function find(x, _param) {
       _param = c < 0 ? param._0 : param._3;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -794,10 +808,11 @@ function min_binding(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -814,10 +829,11 @@ function max_binding(_param) {
       _param = param._3;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -830,11 +846,12 @@ function remove_min_binding(param) {
       return param._3;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.remove_min_elt"
+            }
+          });
 }
 
 function remove(x, param) {
@@ -1060,15 +1077,16 @@ function merge(f, s1, s2) {
     var match$1 = split(v2, s1);
     return concat_or_join(merge(f, match$1[0], s2._0), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2._2)), merge(f, match$1[2], s2._3));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/inline_map2_test.ml",
-          270,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/inline_map2_test.ml",
+                270,
+                10
+              ]
+            }
+          });
 }
 
 function filter(p, param) {
@@ -1334,17 +1352,19 @@ function bal$1(l, x, d, r) {
       if (lr) {
         return create$1(create$1(ll, lv, ld, lr._0), lr._1, lr._2, create$1(lr._3, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
-    }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
+    }
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -1366,17 +1386,19 @@ function bal$1(l, x, d, r) {
     if (rl) {
       return create$1(create$1(l, x, d, rl._0), rl._1, rl._2, create$1(rl._3, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function is_empty$1(param) {
@@ -1428,10 +1450,11 @@ function find$1(x, _param) {
       _param = c < 0 ? param._0 : param._3;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1464,10 +1487,11 @@ function min_binding$1(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1484,10 +1508,11 @@ function max_binding$1(_param) {
       _param = param._3;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1500,11 +1525,12 @@ function remove_min_binding$1(param) {
       return param._3;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.remove_min_elt"
+            }
+          });
 }
 
 function remove$1(x, param) {
@@ -1730,15 +1756,16 @@ function merge$1(f, s1, s2) {
     var match$1 = split$1(v2, s1);
     return concat_or_join$1(merge$1(f, match$1[0], s2._0), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2._2)), merge$1(f, match$1[2], s2._3));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/inline_map2_test.ml",
-          270,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/inline_map2_test.ml",
+                270,
+                10
+              ]
+            }
+          });
 }
 
 function filter$1(p, param) {
diff --git a/jscomp/test/dist/jscomp/test/inline_map_test.js b/jscomp/test/dist/jscomp/test/inline_map_test.js
index 65c3e1f080..fa7b8dc177 100644
--- a/jscomp/test/dist/jscomp/test/inline_map_test.js
+++ b/jscomp/test/dist/jscomp/test/inline_map_test.js
@@ -41,17 +41,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -73,17 +75,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add(x, data, param) {
@@ -127,10 +131,11 @@ function find(x, _param) {
       _param = c < 0 ? param._0 : param._3;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/inline_record_test.js b/jscomp/test/dist/jscomp/test/inline_record_test.js
index 2c0ea949b2..af959a6eb0 100644
--- a/jscomp/test/dist/jscomp/test/inline_record_test.js
+++ b/jscomp/test/dist/jscomp/test/inline_record_test.js
@@ -67,15 +67,16 @@ var tmp;
 if (A0 === A0) {
   tmp = 3;
 } else {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/inline_record_test.ml",
-          46,
-          54
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/inline_record_test.ml",
+                46,
+                54
+              ]
+            }
+          });
 }
 
 eq("File \"jscomp/test/inline_record_test.ml\", line 46, characters 6-13", tmp, 3);
@@ -110,15 +111,16 @@ var tmp$1;
 if (v4.TAG === /* A0 */0) {
   tmp$1 = v4.x;
 } else {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/inline_record_test.ml",
-          64,
-          48
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/inline_record_test.ml",
+                64,
+                48
+              ]
+            }
+          });
 }
 
 eq("File \"jscomp/test/inline_record_test.ml\", line 64, characters 6-13", tmp$1, 11);
@@ -126,15 +128,16 @@ eq("File \"jscomp/test/inline_record_test.ml\", line 64, characters 6-13", tmp$1
 var tmp$2;
 
 if (v5.TAG === /* A0 */0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/inline_record_test.ml",
-          66,
-          48
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/inline_record_test.ml",
+                66,
+                48
+              ]
+            }
+          });
 }
 
 tmp$2 = v5.z;
@@ -168,15 +171,16 @@ var tmp$3;
 if (v6.MEL_EXN_ID === A4) {
   tmp$3 = v6.x;
 } else {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/inline_record_test.ml",
-          82,
-          49
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/inline_record_test.ml",
+                82,
+                49
+              ]
+            }
+          });
 }
 
 eq("File \"jscomp/test/inline_record_test.ml\", line 82, characters 6-13", tmp$3, 11);
diff --git a/jscomp/test/dist/jscomp/test/int64_string_test.js b/jscomp/test/dist/jscomp/test/int64_string_test.js
index b2eb62ea27..d23778a8af 100644
--- a/jscomp/test/dist/jscomp/test/int64_string_test.js
+++ b/jscomp/test/dist/jscomp/test/int64_string_test.js
@@ -1308,28 +1308,30 @@ var random_data = {
 Belt__Belt_List.forEach(random_data, (function (u) {
         if (u) {
           if (u.tl) {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/int64_string_test.ml",
-                    161,
-                    9
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/int64_string_test.ml",
+                          161,
+                          9
+                        ]
+                      }
+                    });
           }
           var match = u.hd;
           return eq("File \"jscomp/test/int64_string_test.ml\", line 160, characters 21-28", Caml_format.caml_int64_format("%d", match[0]), match[1]);
         }
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/int64_string_test.ml",
-                161,
-                9
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/int64_string_test.ml",
+                      161,
+                      9
+                    ]
+                  }
+                });
       }));
 
 eq("File \"jscomp/test/int64_string_test.ml\", line 164, characters 7-14", Caml_format.caml_int64_format("%d", [
diff --git a/jscomp/test/dist/jscomp/test/int_map.js b/jscomp/test/dist/jscomp/test/int_map.js
index 094d5ff6fe..400e7a7841 100644
--- a/jscomp/test/dist/jscomp/test/int_map.js
+++ b/jscomp/test/dist/jscomp/test/int_map.js
@@ -59,17 +59,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -91,17 +93,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function is_empty(param) {
@@ -167,10 +171,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -207,10 +212,11 @@ function find_first(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -284,10 +290,11 @@ function find_last(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -372,10 +379,11 @@ function min_binding(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -410,10 +418,11 @@ function max_binding(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -443,11 +452,12 @@ function remove_min_binding(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.remove_min_elt"
+            }
+          });
 }
 
 function merge(t1, t2) {
@@ -758,15 +768,16 @@ function merge$1(f, s1, s2) {
     var match$1 = split(v2, s1);
     return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/stdlib/map.ml",
-          408,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/stdlib/map.ml",
+                408,
+                10
+              ]
+            }
+          });
 }
 
 function union(f, s1, s2) {
diff --git a/jscomp/test/dist/jscomp/test/internal_unused_test.js b/jscomp/test/dist/jscomp/test/internal_unused_test.js
index e704a15466..792756c85f 100644
--- a/jscomp/test/dist/jscomp/test/internal_unused_test.js
+++ b/jscomp/test/dist/jscomp/test/internal_unused_test.js
@@ -8,10 +8,11 @@ console.log(3);
 var A = /* @__PURE__ */Caml_exceptions.create("Internal_unused_test.P1.A");
 
 function f(param) {
-  throw {
-        MEL_EXN_ID: A,
-        Error: new Error()
-      };
+  throw new Error(A, {
+            cause: {
+              MEL_EXN_ID: A
+            }
+          });
 }
 
 var c = 5;
diff --git a/jscomp/test/dist/jscomp/test/js_exception_catch_test.js b/jscomp/test/dist/jscomp/test/js_exception_catch_test.js
index 8842a81543..4eb5c30ea4 100644
--- a/jscomp/test/dist/jscomp/test/js_exception_catch_test.js
+++ b/jscomp/test/dist/jscomp/test/js_exception_catch_test.js
@@ -74,7 +74,9 @@ catch (raw_exn){
                   };
           }));
   } else {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -135,79 +137,90 @@ eq("File \"jscomp/test/js_exception_catch_test.ml\", line 43, characters 5-12",
         }), "No_error");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 44, characters 5-12", test(function (param) {
-          throw {
-                MEL_EXN_ID: Stdlib.Not_found,
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Not_found, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Not_found
+                    }
+                  });
         }), "Not_found");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 45, characters 5-12", test(function (param) {
-          throw {
-                MEL_EXN_ID: "Invalid_argument",
-                _1: "x",
-                Error: new Error()
-              };
+          throw new Error("Invalid_argument", {
+                    cause: {
+                      MEL_EXN_ID: "Invalid_argument",
+                      _1: "x"
+                    }
+                  });
         }), "Invalid_argument");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 46, characters 5-12", test(function (param) {
-          throw {
-                MEL_EXN_ID: "Invalid_argument",
-                _1: "",
-                Error: new Error()
-              };
+          throw new Error("Invalid_argument", {
+                    cause: {
+                      MEL_EXN_ID: "Invalid_argument",
+                      _1: ""
+                    }
+                  });
         }), "Invalid_any");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 47, characters 5-12", test(function (param) {
-          throw {
-                MEL_EXN_ID: A,
-                _1: 2,
-                Error: new Error()
-              };
+          throw new Error(A, {
+                    cause: {
+                      MEL_EXN_ID: A,
+                      _1: 2
+                    }
+                  });
         }), "A2");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 48, characters 5-12", test(function (param) {
-          throw {
-                MEL_EXN_ID: A,
-                _1: 3,
-                Error: new Error()
-              };
+          throw new Error(A, {
+                    cause: {
+                      MEL_EXN_ID: A,
+                      _1: 3
+                    }
+                  });
         }), "A_any");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 49, characters 5-12", test(function (param) {
-          throw {
-                MEL_EXN_ID: B,
-                Error: new Error()
-              };
+          throw new Error(B, {
+                    cause: {
+                      MEL_EXN_ID: B
+                    }
+                  });
         }), "B");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 50, characters 5-12", test(function (param) {
-          throw {
-                MEL_EXN_ID: C,
-                _1: 1,
-                _2: 2,
-                Error: new Error()
-              };
+          throw new Error(C, {
+                    cause: {
+                      MEL_EXN_ID: C,
+                      _1: 1,
+                      _2: 2
+                    }
+                  });
         }), "C");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 51, characters 5-12", test(function (param) {
-          throw {
-                MEL_EXN_ID: C,
-                _1: 0,
-                _2: 2,
-                Error: new Error()
-              };
+          throw new Error(C, {
+                    cause: {
+                      MEL_EXN_ID: C,
+                      _1: 0,
+                      _2: 2
+                    }
+                  });
         }), "C_any");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 52, characters 5-12", test(function (param) {
-          throw new Error("x");
+          throw new Error(new Error("x").MEL_EXN_ID, {
+                    cause: new Error("x")
+                  });
         }), "Js_error");
 
 eq("File \"jscomp/test/js_exception_catch_test.ml\", line 53, characters 5-12", test(function (param) {
-          throw {
-                MEL_EXN_ID: "Failure",
-                _1: "x",
-                Error: new Error()
-              };
+          throw new Error("Failure", {
+                    cause: {
+                      MEL_EXN_ID: "Failure",
+                      _1: "x"
+                    }
+                  });
         }), "Any");
 
 Mt.from_pair_suites("Js_exception_catch_test", suites.contents);
diff --git a/jscomp/test/dist/jscomp/test/js_json_test.js b/jscomp/test/dist/jscomp/test/js_json_test.js
index 61f8fe1868..901d09498d 100644
--- a/jscomp/test/dist/jscomp/test/js_json_test.js
+++ b/jscomp/test/dist/jscomp/test/js_json_test.js
@@ -97,28 +97,30 @@ add_test("File \"jscomp/test/js_json_test.ml\", line 24, characters 11-18", (fun
         ty2._0.forEach(function (x) {
               var ty3 = Js__Js_json.classify(x);
               if (typeof ty3 === "number") {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/js_json_test.ml",
-                        38,
-                        21
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/js_json_test.ml",
+                              38,
+                              21
+                            ]
+                          }
+                        });
               }
               if (ty3.TAG === /* JSONNumber */1) {
                 return ;
               }
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/js_json_test.ml",
-                      38,
-                      21
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/js_json_test.ml",
+                            38,
+                            21
+                          ]
+                        }
+                      });
             });
         return {
                 TAG: /* Ok */4,
@@ -258,15 +260,16 @@ function option_get(param) {
   if (param !== undefined) {
     return Caml_option.valFromOption(param);
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/js_json_test.ml",
-          103,
-          36
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/js_json_test.ml",
+                103,
+                36
+              ]
+            }
+          });
 }
 
 var dict = {};
diff --git a/jscomp/test/dist/jscomp/test/js_promise_basic_test.js b/jscomp/test/dist/jscomp/test/js_promise_basic_test.js
index a1c913b20b..5c85e62f49 100644
--- a/jscomp/test/dist/jscomp/test/js_promise_basic_test.js
+++ b/jscomp/test/dist/jscomp/test/js_promise_basic_test.js
@@ -37,23 +37,25 @@ function assert_bool(b) {
   if (b) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Invalid_argument,
-        _1: "Assertion Failure.",
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Invalid_argument, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Invalid_argument,
+              _1: "Assertion Failure."
+            }
+          });
 }
 
 function fail(param) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/js_promise_basic_test.ml",
-          17,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/js_promise_basic_test.ml",
+                17,
+                2
+              ]
+            }
+          });
 }
 
 function thenTest(param) {
@@ -79,15 +81,16 @@ function assertIsNotFound(x) {
   if (match !== undefined) {
     return h;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/js_promise_basic_test.ml",
-          34,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/js_promise_basic_test.ml",
+                34,
+                9
+              ]
+            }
+          });
 }
 
 function catchTest(param) {
@@ -150,15 +153,16 @@ function orElseRejectedRejectTest(param) {
               if (match !== undefined) {
                 return h;
               }
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/js_promise_basic_test.ml",
-                      76,
-                      19
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/js_promise_basic_test.ml",
+                            76,
+                            19
+                          ]
+                        }
+                      });
             });
 }
 
diff --git a/jscomp/test/dist/jscomp/test/large_obj_test.js b/jscomp/test/dist/jscomp/test/large_obj_test.js
index 5f520b1937..8a279a6add 100644
--- a/jscomp/test/dist/jscomp/test/large_obj_test.js
+++ b/jscomp/test/dist/jscomp/test/large_obj_test.js
@@ -591,15 +591,16 @@ CamlinternalOO.init_class($$class);
 var raw_object = obj_init(undefined);
 
 if (Caml_oo_curry.js1(291536124, 1, raw_object) !== 34) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/large_obj_test.ml",
-          124,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/large_obj_test.ml",
+                124,
+                10
+              ]
+            }
+          });
 }
 
 function raw_class_init($$class) {
@@ -917,15 +918,16 @@ var raw_class = CamlinternalOO.make_class(shared$2, raw_class_init);
 var v = Curry._2(raw_class[0], undefined, 3);
 
 if (Caml_oo_curry.js1(291536121, 2, v) !== 56) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/large_obj_test.ml",
-          251,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/large_obj_test.ml",
+                251,
+                2
+              ]
+            }
+          });
 }
 
 exports.raw_object = raw_object;
diff --git a/jscomp/test/dist/jscomp/test/lazy_test.js b/jscomp/test/dist/jscomp/test/lazy_test.js
index 6fbab68007..2c46d75301 100644
--- a/jscomp/test/dist/jscomp/test/lazy_test.js
+++ b/jscomp/test/dist/jscomp/test/lazy_test.js
@@ -39,15 +39,16 @@ function f(param) {
   if (x !== undefined) {
     return 1;
   }
-  throw {
-        MEL_EXN_ID: "Match_failure",
-        _1: [
-          "lazy_test.ml",
-          9,
-          8
-        ],
-        Error: new Error()
-      };
+  throw new Error("Match_failure", {
+            cause: {
+              MEL_EXN_ID: "Match_failure",
+              _1: [
+                "lazy_test.ml",
+                9,
+                8
+              ]
+            }
+          });
 }
 
 var s = {
@@ -82,7 +83,9 @@ catch (raw_exn){
   if (exn.MEL_EXN_ID === Stdlib.Match_failure) {
     h = 2;
   } else {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -134,10 +137,11 @@ var f006 = {
 var f007 = {
   LAZY_DONE: false,
   VAL: (function () {
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     })
 };
 
@@ -145,10 +149,11 @@ var f008 = {
   LAZY_DONE: false,
   VAL: (function () {
       console.log("hi");
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     })
 };
 
@@ -331,10 +336,11 @@ Mt.from_pair_suites("Lazy_test", {
                                           _0: !Stdlib__Lazy.is_val({
                                                 LAZY_DONE: false,
                                                 VAL: (function () {
-                                                    throw {
-                                                          MEL_EXN_ID: Stdlib.Not_found,
-                                                          Error: new Error()
-                                                        };
+                                                    throw new Error(Stdlib.Not_found, {
+                                                              cause: {
+                                                                MEL_EXN_ID: Stdlib.Not_found
+                                                              }
+                                                            });
                                                   })
                                               })
                                         };
diff --git a/jscomp/test/dist/jscomp/test/lexer_test.js b/jscomp/test/dist/jscomp/test/lexer_test.js
index baaed6d635..276ff2a192 100644
--- a/jscomp/test/dist/jscomp/test/lexer_test.js
+++ b/jscomp/test/dist/jscomp/test/lexer_test.js
@@ -43,10 +43,11 @@ function from_tokens(lst) {
       l.contents = match.tl;
       return match.hd;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.End_of_file,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.End_of_file, {
+              cause: {
+                MEL_EXN_ID: Stdlib.End_of_file
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/libqueue_test.js b/jscomp/test/dist/jscomp/test/libqueue_test.js
index f6818df143..98d7150a13 100644
--- a/jscomp/test/dist/jscomp/test/libqueue_test.js
+++ b/jscomp/test/dist/jscomp/test/libqueue_test.js
@@ -50,7 +50,9 @@ function does_raise(f, q) {
     if (exn.MEL_EXN_ID === Stdlib__Queue.Empty) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -61,15 +63,16 @@ var q = {
 };
 
 if (!(Caml_obj.caml_equal(to_list(q), /* [] */0) && q.length === 0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          28,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                28,
+                25
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.add(1, q);
@@ -78,15 +81,16 @@ if (!(Caml_obj.caml_equal(to_list(q), {
           hd: 1,
           tl: /* [] */0
         }) && q.length === 1)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          29,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                29,
+                25
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.add(2, q);
@@ -98,15 +102,16 @@ if (!(Caml_obj.caml_equal(to_list(q), {
             tl: /* [] */0
           }
         }) && q.length === 2)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          30,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                30,
+                25
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.add(3, q);
@@ -121,15 +126,16 @@ if (!(Caml_obj.caml_equal(to_list(q), {
             }
           }
         }) && q.length === 3)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          31,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                31,
+                25
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.add(4, q);
@@ -147,27 +153,29 @@ if (!(Caml_obj.caml_equal(to_list(q), {
             }
           }
         }) && q.length === 4)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          32,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                32,
+                25
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.take(q) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          33,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                33,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(to_list(q), {
@@ -180,27 +188,29 @@ if (!(Caml_obj.caml_equal(to_list(q), {
             }
           }
         }) && q.length === 3)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          33,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                33,
+                25
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.take(q) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          34,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                34,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(to_list(q), {
@@ -210,78 +220,84 @@ if (!(Caml_obj.caml_equal(to_list(q), {
             tl: /* [] */0
           }
         }) && q.length === 2)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          34,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                34,
+                25
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.take(q) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          35,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                35,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(to_list(q), {
           hd: 4,
           tl: /* [] */0
         }) && q.length === 1)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          35,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                35,
+                25
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.take(q) !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          36,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                36,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Caml_obj.caml_equal(to_list(q), /* [] */0) && q.length === 0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          36,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                36,
+                25
+              ]
+            }
+          });
 }
 
 if (!does_raise(Stdlib__Queue.take, q)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          37,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                37,
+                2
+              ]
+            }
+          });
 }
 
 var q$1 = {
@@ -293,65 +309,70 @@ var q$1 = {
 Stdlib__Queue.add(1, q$1);
 
 if (Stdlib__Queue.take(q$1) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          42,
-          13
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                42,
+                13
+              ]
+            }
+          });
 }
 
 if (!does_raise(Stdlib__Queue.take, q$1)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          42,
-          36
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                42,
+                36
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.add(2, q$1);
 
 if (Stdlib__Queue.take(q$1) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          43,
-          13
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                43,
+                13
+              ]
+            }
+          });
 }
 
 if (!does_raise(Stdlib__Queue.take, q$1)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          43,
-          36
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                43,
+                36
+              ]
+            }
+          });
 }
 
 if (q$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          44,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                44,
+                2
+              ]
+            }
+          });
 }
 
 var q$2 = {
@@ -363,139 +384,150 @@ var q$2 = {
 Stdlib__Queue.add(1, q$2);
 
 if (Stdlib__Queue.peek(q$2) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          49,
-          13
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                49,
+                13
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.add(2, q$2);
 
 if (Stdlib__Queue.peek(q$2) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          50,
-          13
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                50,
+                13
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.add(3, q$2);
 
 if (Stdlib__Queue.peek(q$2) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          51,
-          13
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                51,
+                13
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.peek(q$2) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          52,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                52,
+                2
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.take(q$2) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          52,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                52,
+                25
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.peek(q$2) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          53,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                53,
+                2
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.take(q$2) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          53,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                53,
+                25
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.peek(q$2) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          54,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                54,
+                2
+              ]
+            }
+          });
 }
 
 if (Stdlib__Queue.take(q$2) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          54,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                54,
+                25
+              ]
+            }
+          });
 }
 
 if (!does_raise(Stdlib__Queue.peek, q$2)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          55,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                55,
+                2
+              ]
+            }
+          });
 }
 
 if (!does_raise(Stdlib__Queue.peek, q$2)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          56,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                56,
+                2
+              ]
+            }
+          });
 }
 
 var q$3 = {
@@ -511,27 +543,29 @@ for(var i = 1; i <= 10; ++i){
 Stdlib__Queue.clear(q$3);
 
 if (q$3.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          63,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                63,
+                2
+              ]
+            }
+          });
 }
 
 if (!does_raise(Stdlib__Queue.take, q$3)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          64,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                64,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(q$3, {
@@ -539,29 +573,31 @@ if (!Caml_obj.caml_equal(q$3, {
         first: /* Nil */0,
         last: /* Nil */0
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          65,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                65,
+                2
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.add(42, q$3);
 
 if (Stdlib__Queue.take(q$3) !== 42) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          67,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                67,
+                2
+              ]
+            }
+          });
 }
 
 var q1 = {
@@ -607,15 +643,16 @@ if (!Caml_obj.caml_equal(to_list(q1), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          74,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                74,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q2), {
@@ -649,67 +686,72 @@ if (!Caml_obj.caml_equal(to_list(q2), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          75,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                75,
+                2
+              ]
+            }
+          });
 }
 
 if (q1.length !== 10) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          76,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                76,
+                2
+              ]
+            }
+          });
 }
 
 if (q2.length !== 10) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          77,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                77,
+                2
+              ]
+            }
+          });
 }
 
 for(var i$2 = 1; i$2 <= 10; ++i$2){
   if (Stdlib__Queue.take(q1) !== i$2) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/libqueue_test.ml",
-            79,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/libqueue_test.ml",
+                  79,
+                  4
+                ]
+              }
+            });
   }
   
 }
 
 for(var i$3 = 1; i$3 <= 10; ++i$3){
   if (Stdlib__Queue.take(q2) !== i$3) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/libqueue_test.ml",
-            82,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/libqueue_test.ml",
+                  82,
+                  4
+                ]
+              }
+            });
   }
   
 }
@@ -721,92 +763,99 @@ var q$4 = {
 };
 
 if (q$4.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          88,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                88,
+                2
+              ]
+            }
+          });
 }
 
 for(var i$4 = 1; i$4 <= 10; ++i$4){
   Stdlib__Queue.add(i$4, q$4);
   if (q$4.length !== i$4) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/libqueue_test.ml",
-            91,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/libqueue_test.ml",
+                  91,
+                  4
+                ]
+              }
+            });
   }
   if (q$4.length === 0) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/libqueue_test.ml",
-            92,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/libqueue_test.ml",
+                  92,
+                  4
+                ]
+              }
+            });
   }
   
 }
 
 for(var i$5 = 10; i$5 >= 1; --i$5){
   if (q$4.length !== i$5) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/libqueue_test.ml",
-            95,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/libqueue_test.ml",
+                  95,
+                  4
+                ]
+              }
+            });
   }
   if (q$4.length === 0) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/libqueue_test.ml",
-            96,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/libqueue_test.ml",
+                  96,
+                  4
+                ]
+              }
+            });
   }
   Stdlib__Queue.take(q$4);
 }
 
 if (q$4.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          99,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                99,
+                2
+              ]
+            }
+          });
 }
 
 if (q$4.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          100,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                100,
+                2
+              ]
+            }
+          });
 }
 
 var q$5 = {
@@ -825,15 +874,16 @@ var i$7 = {
 
 Stdlib__Queue.iter((function (j) {
         if (i$7.contents !== j) {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/libqueue_test.ml",
-                  107,
-                  19
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/libqueue_test.ml",
+                        107,
+                        19
+                      ]
+                    }
+                  });
         }
         i$7.contents = i$7.contents + 1 | 0;
       }), q$5);
@@ -851,101 +901,109 @@ var q2$1 = {
 };
 
 if (q1$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          112,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                112,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q1$1), /* [] */0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          112,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                112,
+                28
+              ]
+            }
+          });
 }
 
 if (q2$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          113,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                113,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q2$1), /* [] */0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          113,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                113,
+                28
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.transfer(q1$1, q2$1);
 
 if (q1$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          115,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                115,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q1$1), /* [] */0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          115,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                115,
+                28
+              ]
+            }
+          });
 }
 
 if (q2$1.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          116,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                116,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q2$1), /* [] */0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          116,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                116,
+                28
+              ]
+            }
+          });
 }
 
 var q1$2 = {
@@ -965,15 +1023,16 @@ for(var i$8 = 1; i$8 <= 4; ++i$8){
 }
 
 if (q1$2.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          122,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                122,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q1$2), {
@@ -989,77 +1048,83 @@ if (!Caml_obj.caml_equal(to_list(q1$2), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          122,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                122,
+                28
+              ]
+            }
+          });
 }
 
 if (q2$2.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          123,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                123,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q2$2), /* [] */0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          123,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                123,
+                28
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.transfer(q1$2, q2$2);
 
 if (q1$2.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          125,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                125,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q1$2), /* [] */0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          125,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                125,
+                28
+              ]
+            }
+          });
 }
 
 if (q2$2.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          126,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                126,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q2$2), {
@@ -1075,15 +1140,16 @@ if (!Caml_obj.caml_equal(to_list(q2$2), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          126,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                126,
+                28
+              ]
+            }
+          });
 }
 
 var q1$3 = {
@@ -1103,39 +1169,42 @@ for(var i$9 = 5; i$9 <= 8; ++i$9){
 }
 
 if (q1$3.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          132,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                132,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q1$3), /* [] */0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          132,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                132,
+                28
+              ]
+            }
+          });
 }
 
 if (q2$3.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          133,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                133,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q2$3), {
@@ -1151,53 +1220,57 @@ if (!Caml_obj.caml_equal(to_list(q2$3), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          133,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                133,
+                28
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.transfer(q1$3, q2$3);
 
 if (q1$3.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          135,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                135,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q1$3), /* [] */0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          135,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                135,
+                28
+              ]
+            }
+          });
 }
 
 if (q2$3.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          136,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                136,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q2$3), {
@@ -1213,15 +1286,16 @@ if (!Caml_obj.caml_equal(to_list(q2$3), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          136,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                136,
+                28
+              ]
+            }
+          });
 }
 
 var q1$4 = {
@@ -1245,15 +1319,16 @@ for(var i$11 = 5; i$11 <= 8; ++i$11){
 }
 
 if (q1$4.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          143,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                143,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q1$4), {
@@ -1269,27 +1344,29 @@ if (!Caml_obj.caml_equal(to_list(q1$4), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          143,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                143,
+                28
+              ]
+            }
+          });
 }
 
 if (q2$4.length !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          144,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                144,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q2$4), {
@@ -1305,53 +1382,57 @@ if (!Caml_obj.caml_equal(to_list(q2$4), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          144,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                144,
+                28
+              ]
+            }
+          });
 }
 
 Stdlib__Queue.transfer(q1$4, q2$4);
 
 if (q1$4.length !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          146,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                146,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q1$4), /* [] */0)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          146,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                146,
+                28
+              ]
+            }
+          });
 }
 
 if (q2$4.length !== 8) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          147,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                147,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(to_list(q2$4), {
@@ -1379,15 +1460,16 @@ if (!Caml_obj.caml_equal(to_list(q2$4), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/libqueue_test.ml",
-          147,
-          28
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/libqueue_test.ml",
+                147,
+                28
+              ]
+            }
+          });
 }
 
 console.log("OK");
diff --git a/jscomp/test/dist/jscomp/test/map_find_test.js b/jscomp/test/dist/jscomp/test/map_find_test.js
index b26f08befd..b2434737c7 100644
--- a/jscomp/test/dist/jscomp/test/map_find_test.js
+++ b/jscomp/test/dist/jscomp/test/map_find_test.js
@@ -48,17 +48,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -80,17 +82,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add(x, data, m) {
@@ -148,10 +152,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -224,17 +229,19 @@ function bal$1(l, x, d, r) {
       if (lr) {
         return create$1(create$1(ll, lv, ld, lr.l), lr.v, lr.d, create$1(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -256,17 +263,19 @@ function bal$1(l, x, d, r) {
     if (rl) {
       return create$1(create$1(l, x, d, rl.l), rl.v, rl.d, create$1(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add$1(x, data, m) {
@@ -324,10 +333,11 @@ function find$1(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/map_test.js b/jscomp/test/dist/jscomp/test/map_test.js
index 20a2855af3..2a9ce90583 100644
--- a/jscomp/test/dist/jscomp/test/map_test.js
+++ b/jscomp/test/dist/jscomp/test/map_test.js
@@ -49,17 +49,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -81,17 +83,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add(x, data, m) {
@@ -267,17 +271,19 @@ function bal$1(l, x, d, r) {
       if (lr) {
         return create$1(create$1(ll, lv, ld, lr.l), lr.v, lr.d, create$1(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -299,17 +305,19 @@ function bal$1(l, x, d, r) {
     if (rl) {
       return create$1(create$1(l, x, d, rl.l), rl.v, rl.d, create$1(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add$1(x, data, m) {
@@ -367,10 +375,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/mario_game.js b/jscomp/test/dist/jscomp/test/mario_game.js
index 04909bf207..a37798b5b9 100644
--- a/jscomp/test/dist/jscomp/test/mario_game.js
+++ b/jscomp/test/dist/jscomp/test/mario_game.js
@@ -1481,11 +1481,12 @@ function game_win(ctx) {
   ctx.fillStyle = "white";
   ctx.font = "20px 'Press Start 2P'";
   ctx.fillText("You win!", 180, 128);
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "Game over.",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "Game over."
+            }
+          });
 }
 
 function game_loss(ctx) {
@@ -1495,11 +1496,12 @@ function game_loss(ctx) {
   ctx.fillStyle = "white";
   ctx.font = "20px 'Press Start 2P'";
   ctx.fillText("GAME OVER. You lose!", 60, 128);
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "Game over.",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "Game over."
+            }
+          });
 }
 
 var Draw = {
@@ -2391,11 +2393,12 @@ function choose_enemy_typ(typ) {
     case 2 :
         return /* Goomba */0;
     default:
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "Shouldn't reach here",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "Shouldn't reach here"
+                }
+              });
   }
 }
 
@@ -2414,11 +2417,12 @@ function choose_sblock_typ(typ) {
     case 4 :
         return /* Ground */5;
     default:
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "Shouldn't reach here",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "Shouldn't reach here"
+                }
+              });
   }
 }
 
@@ -2929,11 +2933,12 @@ function choose_block_pattern(blockw, blockh, cbx, cby, prob) {
                 tl: /* [] */0
               };
     default:
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "Shouldn't reach here",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "Shouldn't reach here"
+                }
+              });
   }
 }
 
@@ -3217,11 +3222,12 @@ function load(param) {
               },
               _1: "cant find canvas %s \n"
             }), canvas_id);
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "fail",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "fail"
+              }
+            });
   }
   var context = canvas.getContext("2d");
   document.addEventListener("keydown", keydown, true);
diff --git a/jscomp/test/dist/jscomp/test/noassert.js b/jscomp/test/dist/jscomp/test/noassert.js
index ead896e11a..4d2c65a704 100644
--- a/jscomp/test/dist/jscomp/test/noassert.js
+++ b/jscomp/test/dist/jscomp/test/noassert.js
@@ -3,15 +3,16 @@
 
 
 function f(param) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/noassert.ml",
-          5,
-          11
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/noassert.ml",
+                5,
+                11
+              ]
+            }
+          });
 }
 
 function h(param) {
diff --git a/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js b/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js
index 93de45ca17..32b6851e85 100644
--- a/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js
+++ b/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js
@@ -41,7 +41,9 @@ try {
 catch (raw_exn){
   var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
   if (exn.MEL_EXN_ID !== Stdlib.Not_found) {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   
 }
@@ -73,10 +75,11 @@ var Fatal_error = /* @__PURE__ */Caml_exceptions.create("Ocaml_parsetree_test.Mi
 function fatal_error(msg) {
   Stdlib.prerr_string(">> Fatal error: ");
   console.error(msg);
-  throw {
-        MEL_EXN_ID: Fatal_error,
-        Error: new Error()
-      };
+  throw new Error(Fatal_error, {
+            cause: {
+              MEL_EXN_ID: Fatal_error
+            }
+          });
 }
 
 function create_hashtable(size, init) {
@@ -208,21 +211,23 @@ function style_of_tag(param) {
       case "warning" :
           return cur_styles.contents.warning;
       default:
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     }
   } else {
-    throw {
-          MEL_EXN_ID: "Match_failure",
-          _1: [
-            "misc.ml",
-            428,
-            19
-          ],
-          Error: new Error()
-        };
+    throw new Error("Match_failure", {
+              cause: {
+                MEL_EXN_ID: "Match_failure",
+                _1: [
+                  "misc.ml",
+                  428,
+                  19
+                ]
+              }
+            });
   }
 }
 
@@ -248,7 +253,9 @@ function set_color_tag_handling(ppf) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         return Curry._1(partial_arg, param);
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   var functions$p_mark_close_stag = function (param) {
@@ -268,7 +275,9 @@ function set_color_tag_handling(ppf) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         return Curry._1(partial_arg$1, param);
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   var functions$p_print_open_stag = functions.print_open_stag;
@@ -621,15 +630,16 @@ function letter(param) {
                 tl: /* [] */0
               };
     default:
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "warnings.ml",
-              176,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "warnings.ml",
+                    176,
+                    9
+                  ]
+                }
+              });
   }
 }
 
@@ -691,11 +701,12 @@ function parse_opt(error, active, flags, s) {
     var match$1 = get_num(0, i$1 + 2 | 0);
     var n2 = match$1[1];
     if (n2 < n1) {
-      throw {
-            MEL_EXN_ID: Stdlib__Arg.Bad,
-            _1: "Ill-formed list of warnings",
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Arg.Bad, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Arg.Bad,
+                  _1: "Ill-formed list of warnings"
+                }
+              });
     }
     return [
             match$1[0],
@@ -713,22 +724,24 @@ function parse_opt(error, active, flags, s) {
       if (c >= 65) {
         if (c >= 97) {
           if (c >= 123) {
-            throw {
-                  MEL_EXN_ID: Stdlib__Arg.Bad,
-                  _1: "Ill-formed list of warnings",
-                  Error: new Error()
-                };
+            throw new Error(Stdlib__Arg.Bad, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib__Arg.Bad,
+                        _1: "Ill-formed list of warnings"
+                      }
+                    });
           }
           Stdlib__List.iter(clear, letter(Caml_string.get(s, i)));
           _i = i + 1 | 0;
           continue ;
         }
         if (c >= 91) {
-          throw {
-                MEL_EXN_ID: Stdlib__Arg.Bad,
-                _1: "Ill-formed list of warnings",
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Arg.Bad, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Arg.Bad,
+                      _1: "Ill-formed list of warnings"
+                    }
+                  });
         }
         Stdlib__List.iter(set, letter(Stdlib__Char.lowercase_ascii(Caml_string.get(s, i))));
         _i = i + 1 | 0;
@@ -738,72 +751,79 @@ function parse_opt(error, active, flags, s) {
         if (c >= 64) {
           return loop_letter_num(set_all, i + 1 | 0);
         }
-        throw {
-              MEL_EXN_ID: Stdlib__Arg.Bad,
-              _1: "Ill-formed list of warnings",
-              Error: new Error()
-            };
+        throw new Error(Stdlib__Arg.Bad, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib__Arg.Bad,
+                    _1: "Ill-formed list of warnings"
+                  }
+                });
       }
       if (c >= 43) {
         switch (c) {
           case 43 :
               return loop_letter_num(set, i + 1 | 0);
           case 44 :
-              throw {
-                    MEL_EXN_ID: Stdlib__Arg.Bad,
-                    _1: "Ill-formed list of warnings",
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib__Arg.Bad, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib__Arg.Bad,
+                          _1: "Ill-formed list of warnings"
+                        }
+                      });
           case 45 :
               return loop_letter_num(clear, i + 1 | 0);
           
         }
       } else {
-        throw {
-              MEL_EXN_ID: Stdlib__Arg.Bad,
-              _1: "Ill-formed list of warnings",
-              Error: new Error()
-            };
+        throw new Error(Stdlib__Arg.Bad, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib__Arg.Bad,
+                    _1: "Ill-formed list of warnings"
+                  }
+                });
       }
     };
   };
   var loop_letter_num = function (myset, i) {
     if (i >= s.length) {
-      throw {
-            MEL_EXN_ID: Stdlib__Arg.Bad,
-            _1: "Ill-formed list of warnings",
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Arg.Bad, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Arg.Bad,
+                  _1: "Ill-formed list of warnings"
+                }
+              });
     }
     var match = Caml_string.get(s, i);
     if (match >= 65) {
       if (match >= 97) {
         if (match >= 123) {
-          throw {
-                MEL_EXN_ID: Stdlib__Arg.Bad,
-                _1: "Ill-formed list of warnings",
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Arg.Bad, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Arg.Bad,
+                      _1: "Ill-formed list of warnings"
+                    }
+                  });
         }
         Stdlib__List.iter(myset, letter(Caml_string.get(s, i)));
         return loop(i + 1 | 0);
       }
       if (match >= 91) {
-        throw {
-              MEL_EXN_ID: Stdlib__Arg.Bad,
-              _1: "Ill-formed list of warnings",
-              Error: new Error()
-            };
+        throw new Error(Stdlib__Arg.Bad, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib__Arg.Bad,
+                    _1: "Ill-formed list of warnings"
+                  }
+                });
       }
       Stdlib__List.iter(myset, letter(Stdlib__Char.lowercase_ascii(Caml_string.get(s, i))));
       return loop(i + 1 | 0);
     }
     if (match > 57 || match < 48) {
-      throw {
-            MEL_EXN_ID: Stdlib__Arg.Bad,
-            _1: "Ill-formed list of warnings",
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Arg.Bad, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Arg.Bad,
+                  _1: "Ill-formed list of warnings"
+                }
+              });
     }
     var match$1 = get_range(i);
     for(var n = match$1[1] ,n_finish = Caml.caml_int_min(match$1[2], 104); n <= n_finish; ++n){
@@ -897,15 +917,16 @@ function message(param) {
               return "the method " + (lab + " is overridden.");
             }
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "warnings.ml",
-                  283,
-                  26
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "warnings.ml",
+                        283,
+                        26
+                      ]
+                    }
+                  });
       case /* Partial_match */3 :
           var s$1 = param._0;
           if (s$1 === "") {
@@ -934,15 +955,16 @@ function message(param) {
               return "the instance variable " + (lab$1 + " is overridden.\nThe behaviour changed in ocaml 3.10 (previous behaviour was hiding.)");
             }
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "warnings.ml",
-                  303,
-                  37
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "warnings.ml",
+                        303,
+                        37
+                      ]
+                    }
+                  });
       case /* Implicit_public_methods */6 :
           return "the following private methods were made public implicitly:\n " + (Stdlib__String.concat(" ", param._0) + ".");
       case /* Undeclared_virtual_method */7 :
@@ -1065,15 +1087,16 @@ function message(param) {
           if (param._2) {
             return "this record of type " + (ty + (" contains fields that are \nnot visible in the current scope: " + (Stdlib__String.concat(" ", slist) + ".\nThey will not be selected if the type becomes unknown.")));
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "warnings.ml",
-                  365,
-                  39
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "warnings.ml",
+                        365,
+                        39
+                      ]
+                    }
+                  });
           break;
       case /* Ambiguous_name */24 :
           var slist$1 = param._0;
@@ -1083,15 +1106,16 @@ function message(param) {
           if (param._2) {
             return "these field labels belong to several types: " + (Stdlib__String.concat(" ", param._1) + "\nThe first one was selected. Please disambiguate if this is wrong.");
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "warnings.ml",
-                  374,
-                  36
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "warnings.ml",
+                        374,
+                        36
+                      ]
+                    }
+                  });
           break;
       case /* Disambiguated_name */25 :
           return "this use of " + (param._0 + " required disambiguation.");
@@ -1337,10 +1361,11 @@ function highlight_terminfo(ppf, num_lines, lb, locs) {
   Stdlib__Format.pp_print_flush(ppf, undefined);
   var pos0 = -lb.lex_abs_pos | 0;
   if (pos0 < 0) {
-    throw {
-          MEL_EXN_ID: Stdlib.Exit,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Exit, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Exit
+              }
+            });
   }
   var lines = num_loc_lines.contents;
   for(var i = pos0 ,i_finish = lb.lex_buffer_len; i < i_finish; ++i){
@@ -1350,10 +1375,11 @@ function highlight_terminfo(ppf, num_lines, lb, locs) {
     
   }
   if (lines >= (num_lines - 2 | 0)) {
-    throw {
-          MEL_EXN_ID: Stdlib.Exit,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Exit, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Exit
+              }
+            });
   }
   Caml_io.caml_ml_flush(Stdlib.stdout);
   Caml_external_polyfill.resolve("caml_terminfo_backup")(lines);
@@ -1390,10 +1416,11 @@ function highlight_terminfo(ppf, num_lines, lb, locs) {
 function highlight_dumb(ppf, lb, loc) {
   var pos0 = -lb.lex_abs_pos | 0;
   if (pos0 < 0) {
-    throw {
-          MEL_EXN_ID: Stdlib.Exit,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Exit, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Exit
+              }
+            });
   }
   var end_pos = (lb.lex_buffer_len - pos0 | 0) - 1 | 0;
   var line_start = 0;
@@ -1528,7 +1555,9 @@ function highlight_locations(ppf, locs) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             norepeat = false;
           } else {
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }
         if (norepeat) {
@@ -1544,7 +1573,9 @@ function highlight_locations(ppf, locs) {
           if (exn$1.MEL_EXN_ID === Stdlib.Exit) {
             return false;
           }
-          throw exn$1;
+          throw new Error(exn$1.MEL_EXN_ID, {
+                    cause: exn$1
+                  });
         }
       } else {
         status.contents = Caml_external_polyfill.resolve("caml_terminfo_setup")(Stdlib.stdout);
@@ -1564,7 +1595,9 @@ function highlight_locations(ppf, locs) {
         if (exn$2.MEL_EXN_ID === Stdlib.Exit) {
           return false;
         }
-        throw exn$2;
+        throw new Error(exn$2.MEL_EXN_ID, {
+                  cause: exn$2
+                });
       }
     }
   };
@@ -2424,7 +2457,9 @@ function get_pre_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -2437,7 +2472,9 @@ function mark_pre_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -2461,7 +2498,9 @@ function get_post_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -2474,7 +2513,9 @@ function mark_post_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -2488,7 +2529,9 @@ function get_info(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -2510,7 +2553,9 @@ function get_text(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -2532,7 +2577,9 @@ function get_pre_extra_text(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -2554,7 +2601,9 @@ function get_post_extra_text(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4027,15 +4076,16 @@ function mkexp_constraint(e, param) {
                 _2: t2
               });
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "parsing/parser.mly",
-          153,
-          18
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "parsing/parser.mly",
+                153,
+                18
+              ]
+            }
+          });
 }
 
 function array_function(str, name) {
@@ -4053,41 +4103,44 @@ function array_function(str, name) {
 }
 
 function unclosed(opening_name, opening_num, closing_name, closing_num) {
-  throw {
-        MEL_EXN_ID: $$Error$1,
-        _1: {
-          TAG: /* Unclosed */0,
-          _0: rhs_loc(opening_num),
-          _1: opening_name,
-          _2: rhs_loc(closing_num),
-          _3: closing_name
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$1, {
+            cause: {
+              MEL_EXN_ID: $$Error$1,
+              _1: {
+                TAG: /* Unclosed */0,
+                _0: rhs_loc(opening_num),
+                _1: opening_name,
+                _2: rhs_loc(closing_num),
+                _3: closing_name
+              }
+            }
+          });
 }
 
 function expecting(pos, nonterm) {
-  throw {
-        MEL_EXN_ID: $$Error$1,
-        _1: {
-          TAG: /* Expecting */1,
-          _0: rhs_loc(pos),
-          _1: nonterm
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$1, {
+            cause: {
+              MEL_EXN_ID: $$Error$1,
+              _1: {
+                TAG: /* Expecting */1,
+                _0: rhs_loc(pos),
+                _1: nonterm
+              }
+            }
+          });
 }
 
 function not_expecting(pos, nonterm) {
-  throw {
-        MEL_EXN_ID: $$Error$1,
-        _1: {
-          TAG: /* Not_expecting */2,
-          _0: rhs_loc(pos),
-          _1: nonterm
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$1, {
+            cause: {
+              MEL_EXN_ID: $$Error$1,
+              _1: {
+                TAG: /* Not_expecting */2,
+                _0: rhs_loc(pos),
+                _1: nonterm
+              }
+            }
+          });
 }
 
 function bigarray_function(str, name) {
@@ -4149,15 +4202,16 @@ function check_variable(vl, loc, v) {
   if (!Stdlib__List.mem(v, vl)) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: $$Error$1,
-        _1: {
-          TAG: /* Variable_in_scope */4,
-          _0: loc,
-          _1: v
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$1, {
+            cause: {
+              MEL_EXN_ID: $$Error$1,
+              _1: {
+                TAG: /* Variable_in_scope */4,
+                _0: loc,
+                _1: v
+              }
+            }
+          });
 }
 
 function varify_constructors(var_names, t) {
@@ -4565,11 +4619,12 @@ var yytransl_block = [
 
 var yyact = [
   (function (param) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "parser",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "parser"
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -4590,10 +4645,11 @@ var yyact = [
       return Stdlib__Parsing.peek_val(__caml_parser_env, 1);
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib.End_of_file,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.End_of_file, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.End_of_file
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -4980,15 +5036,16 @@ var yyact = [
       }
       if (exit === 1) {
         if (Caml_obj.caml_notequal(lbs.lbs_attributes, /* [] */0)) {
-          throw {
-                MEL_EXN_ID: $$Error$1,
-                _1: {
-                  TAG: /* Not_expecting */2,
-                  _0: lbs.lbs_loc,
-                  _1: "attributes"
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$1, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$1,
+                      _1: {
+                        TAG: /* Not_expecting */2,
+                        _0: lbs.lbs_loc,
+                        _1: "attributes"
+                      }
+                    }
+                  });
         }
         var bindings$1 = Stdlib__List.map((function (lb) {
                 return mk$17(lb.lb_loc, lb.lb_attributes, CamlinternalLazy.force(lb.lb_docs), CamlinternalLazy.force(lb.lb_text), lb.lb_pattern, lb.lb_expression);
@@ -5594,39 +5651,42 @@ var yyact = [
       var _3 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       var bindings = Stdlib__List.map((function (lb) {
               if (Caml_obj.caml_notequal(lb.lb_attributes, /* [] */0)) {
-                throw {
-                      MEL_EXN_ID: $$Error$1,
-                      _1: {
-                        TAG: /* Not_expecting */2,
-                        _0: lb.lb_loc,
-                        _1: "item attribute"
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$1, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$1,
+                            _1: {
+                              TAG: /* Not_expecting */2,
+                              _0: lb.lb_loc,
+                              _1: "item attribute"
+                            }
+                          }
+                        });
               }
               return mk$17(lb.lb_loc, undefined, undefined, undefined, lb.lb_pattern, lb.lb_expression);
             }), _1.lbs_bindings);
       if (_1.lbs_extension !== undefined) {
-        throw {
-              MEL_EXN_ID: $$Error$1,
-              _1: {
-                TAG: /* Not_expecting */2,
-                _0: _1.lbs_loc,
-                _1: "extension"
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$1, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$1,
+                    _1: {
+                      TAG: /* Not_expecting */2,
+                      _0: _1.lbs_loc,
+                      _1: "extension"
+                    }
+                  }
+                });
       }
       if (Caml_obj.caml_notequal(_1.lbs_attributes, /* [] */0)) {
-        throw {
-              MEL_EXN_ID: $$Error$1,
-              _1: {
-                TAG: /* Not_expecting */2,
-                _0: _1.lbs_loc,
-                _1: "attributes"
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$1, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$1,
+                    _1: {
+                      TAG: /* Not_expecting */2,
+                      _0: _1.lbs_loc,
+                      _1: "attributes"
+                    }
+                  }
+                });
       }
       return mkclass({
                   TAG: /* Pcl_let */4,
@@ -5807,10 +5867,11 @@ var yyact = [
       var _4 = Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       var _6 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       if (_1 === /* Override */0) {
-        throw {
-              MEL_EXN_ID: Escape_error,
-              Error: new Error()
-            };
+        throw new Error(Escape_error, {
+                  cause: {
+                    MEL_EXN_ID: Escape_error
+                  }
+                });
       }
       return [
               {
@@ -5883,10 +5944,11 @@ var yyact = [
       var _4 = Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       var _6 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       if (_1 === /* Override */0) {
-        throw {
-              MEL_EXN_ID: Escape_error,
-              Error: new Error()
-            };
+        throw new Error(Escape_error, {
+                  cause: {
+                    MEL_EXN_ID: Escape_error
+                  }
+                });
       }
       return [
               {
@@ -5906,10 +5968,11 @@ var yyact = [
       var _4 = Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       var _6 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       if (_1 === /* Override */0) {
-        throw {
-              MEL_EXN_ID: Escape_error,
-              Error: new Error()
-            };
+        throw new Error(Escape_error, {
+                  cause: {
+                    MEL_EXN_ID: Escape_error
+                  }
+                });
       }
       return [
               {
@@ -6448,15 +6511,16 @@ var yyact = [
       var _3 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       var bindings = Stdlib__List.map((function (lb) {
               if (Caml_obj.caml_notequal(lb.lb_attributes, /* [] */0)) {
-                throw {
-                      MEL_EXN_ID: $$Error$1,
-                      _1: {
-                        TAG: /* Not_expecting */2,
-                        _0: lb.lb_loc,
-                        _1: "item attribute"
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$1, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$1,
+                            _1: {
+                              TAG: /* Not_expecting */2,
+                              _0: lb.lb_loc,
+                              _1: "item attribute"
+                            }
+                          }
+                        });
               }
               return mk$17(lb.lb_loc, undefined, undefined, undefined, lb.lb_pattern, lb.lb_expression);
             }), _1.lbs_bindings);
@@ -6568,10 +6632,11 @@ var yyact = [
   (function (__caml_parser_env) {
       Stdlib__Parsing.peek_val(__caml_parser_env, 3);
       Stdlib__Parsing.peek_val(__caml_parser_env, 2);
-      throw {
-            MEL_EXN_ID: Escape_error,
-            Error: new Error()
-          };
+      throw new Error(Escape_error, {
+                cause: {
+                  MEL_EXN_ID: Escape_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -8134,16 +8199,18 @@ var yyact = [
             ];
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Escape_error,
-            Error: new Error()
-          };
+      throw new Error(Escape_error, {
+                cause: {
+                  MEL_EXN_ID: Escape_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Escape_error,
-            Error: new Error()
-          };
+      throw new Error(Escape_error, {
+                cause: {
+                  MEL_EXN_ID: Escape_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -9279,17 +9346,19 @@ var yyact = [
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       if (_2) {
         if (_2.tl) {
-          throw {
-                MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Parsing.Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                    }
+                  });
         }
         return _2.hd;
       }
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.Parse_error, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -9298,17 +9367,19 @@ var yyact = [
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       if (_2) {
         if (_2.tl) {
-          throw {
-                MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Parsing.Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                    }
+                  });
         }
         return _2.hd;
       }
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.Parse_error, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -10090,14 +10161,15 @@ var yyact = [
                 _1: _3
               };
       }
-      throw {
-            MEL_EXN_ID: $$Error$1,
-            _1: {
-              TAG: /* Applicative_path */3,
-              _0: symbol_rloc(undefined)
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$1, {
+                cause: {
+                  MEL_EXN_ID: $$Error$1,
+                  _1: {
+                    TAG: /* Applicative_path */3,
+                    _0: symbol_rloc(undefined)
+                  }
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -10608,53 +10680,60 @@ var yyact = [
             };
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     })
 ];
 
@@ -10720,19 +10799,20 @@ function assert_same_type(lexbuf, x, y) {
   var lhs = type_of_directive(x);
   var rhs = type_of_directive(y);
   if (lhs !== rhs) {
-    throw {
-          MEL_EXN_ID: $$Error$2,
-          _1: {
-            TAG: /* Conditional_expr_expected_type */7,
-            _0: lhs,
-            _1: rhs
-          },
-          _2: curr(lexbuf),
-          Error: new Error()
-        };
-  }
-  return y;
-}
+    throw new Error($$Error$2, {
+              cause: {
+                MEL_EXN_ID: $$Error$2,
+                _1: {
+                  TAG: /* Conditional_expr_expected_type */7,
+                  _0: lhs,
+                  _1: rhs
+                },
+                _2: curr(lexbuf)
+              }
+            });
+  }
+  return y;
+}
 
 var directive_built_in_values = Stdlib__Hashtbl.create(undefined, 51);
 
@@ -10756,7 +10836,9 @@ catch (raw_exn$1){
   if (exn$2.MEL_EXN_ID === Stdlib.Not_found) {
     tmp = "";
   } else {
-    throw exn$2;
+    throw new Error(exn$2.MEL_EXN_ID, {
+              cause: exn$2
+            });
   }
 }
 
@@ -10872,7 +10954,9 @@ function query(loc, str) {
                   _0: false
                 };
         }
-        throw exn$1;
+        throw new Error(exn$1.MEL_EXN_ID, {
+                  cause: exn$1
+                });
       }
       if (exit === 2) {
         try {
@@ -10906,7 +10990,9 @@ function query(loc, str) {
       }
       
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   if (typeof v === "number") {
@@ -10933,12 +11019,13 @@ function value_of_token(loc, t) {
                   _0: true
                 };
       default:
-        throw {
-              MEL_EXN_ID: $$Error$2,
-              _1: /* Unexpected_token_in_conditional */4,
-              _2: loc,
-              Error: new Error()
-            };
+        throw new Error($$Error$2, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$2,
+                    _1: /* Unexpected_token_in_conditional */4,
+                    _2: loc
+                  }
+                });
     }
   } else {
     switch (t.TAG | 0) {
@@ -10960,12 +11047,13 @@ function value_of_token(loc, t) {
       case /* UIDENT */17 :
           return query(loc, t._0);
       default:
-        throw {
-              MEL_EXN_ID: $$Error$2,
-              _1: /* Unexpected_token_in_conditional */4,
-              _2: loc,
-              Error: new Error()
-            };
+        throw new Error($$Error$2, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$2,
+                    _1: /* Unexpected_token_in_conditional */4,
+                    _2: loc
+                  }
+                });
     }
   }
 }
@@ -10986,12 +11074,13 @@ function directive_parse(token_with_comments, lexbuf) {
       if (typeof t === "number") {
         switch (t) {
           case /* EOF */25 :
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: /* Unterminated_if */2,
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: /* Unterminated_if */2,
+                          _2: curr(lexbuf)
+                        }
+                      });
           case /* EOL */100 :
               _param = undefined;
               continue ;
@@ -11012,15 +11101,16 @@ function directive_parse(token_with_comments, lexbuf) {
   };
   var push = function (e) {
     if (look_ahead.contents !== undefined) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "parsing/lexer.mll",
-              312,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "parsing/lexer.mll",
+                    312,
+                    4
+                  ]
+                }
+              });
     }
     look_ahead.contents = e;
   };
@@ -11061,15 +11151,16 @@ function directive_parse(token_with_comments, lexbuf) {
                   var str = rhs._0;
                   var last_index = str.length - 1 | 0;
                   if (last_index < 0) {
-                    throw {
-                          MEL_EXN_ID: $$Error$2,
-                          _1: {
-                            TAG: /* Illegal_semver */6,
-                            _0: str
-                          },
-                          _2: curr_loc,
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$2, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$2,
+                                _1: {
+                                  TAG: /* Illegal_semver */6,
+                                  _0: str
+                                },
+                                _2: curr_loc
+                              }
+                            });
                   }
                   var v = str.charCodeAt(0);
                   var match;
@@ -11088,15 +11179,16 @@ function directive_parse(token_with_comments, lexbuf) {
                       switch (v) {
                         case 60 :
                             if (last_index === 0) {
-                              throw {
-                                    MEL_EXN_ID: $$Error$2,
-                                    _1: {
-                                      TAG: /* Illegal_semver */6,
-                                      _0: str
-                                    },
-                                    _2: curr_loc,
-                                    Error: new Error()
-                                  };
+                              throw new Error($$Error$2, {
+                                        cause: {
+                                          MEL_EXN_ID: $$Error$2,
+                                          _1: {
+                                            TAG: /* Illegal_semver */6,
+                                            _0: str
+                                          },
+                                          _2: curr_loc
+                                        }
+                                      });
                             }
                             match = str[1] === "=" ? [
                                 "Le",
@@ -11111,15 +11203,16 @@ function directive_parse(token_with_comments, lexbuf) {
                             break;
                         case 62 :
                             if (last_index === 0) {
-                              throw {
-                                    MEL_EXN_ID: $$Error$2,
-                                    _1: {
-                                      TAG: /* Illegal_semver */6,
-                                      _0: str
-                                    },
-                                    _2: curr_loc,
-                                    Error: new Error()
-                                  };
+                              throw new Error($$Error$2, {
+                                        cause: {
+                                          MEL_EXN_ID: $$Error$2,
+                                          _1: {
+                                            TAG: /* Illegal_semver */6,
+                                            _0: str
+                                          },
+                                          _2: curr_loc
+                                        }
+                                      });
                             }
                             match = str[1] === "=" ? [
                                 "Ge",
@@ -11178,30 +11271,32 @@ function directive_parse(token_with_comments, lexbuf) {
                 exit$2 = 3;
               }
               if (exit$2 === 3) {
-                throw {
-                      MEL_EXN_ID: $$Error$2,
-                      _1: {
-                        TAG: /* Conditional_expr_expected_type */7,
-                        _0: /* Dir_type_string */3,
-                        _1: type_of_directive(lhs)
-                      },
-                      _2: curr(lexbuf),
-                      Error: new Error()
-                    };
+                throw new Error($$Error$2, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$2,
+                            _1: {
+                              TAG: /* Conditional_expr_expected_type */7,
+                              _0: /* Dir_type_string */3,
+                              _1: type_of_directive(lhs)
+                            },
+                            _2: curr(lexbuf)
+                          }
+                        });
               }
               
             }
             if (exit$1 === 2) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Conditional_expr_expected_type */7,
-                      _0: /* Dir_type_string */3,
-                      _1: type_of_directive(lhs)
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Conditional_expr_expected_type */7,
+                            _0: /* Dir_type_string */3,
+                            _1: type_of_directive(lhs)
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
             break;
         case "<=" :
@@ -11245,15 +11340,16 @@ function directive_parse(token_with_comments, lexbuf) {
         exit$4 = 2;
       }
       if (exit$4 === 2) {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "parsing/lexer.mll",
-                331,
-                17
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "parsing/lexer.mll",
+                      331,
+                      17
+                    ]
+                  }
+                });
       }
       var curr_loc$1 = curr(lexbuf);
       var rhs$1 = value_of_token(curr_loc$1, token(undefined));
@@ -11296,36 +11392,39 @@ function directive_parse(token_with_comments, lexbuf) {
             if (match === 81) {
               return v;
             }
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: /* Unterminated_paren_in_conditional */1,
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: /* Unterminated_paren_in_conditional */1,
+                        _2: curr(lexbuf)
+                      }
+                    });
         case /* TRUE */91 :
             return true;
         default:
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unexpected_token_in_conditional */4,
-                _2: curr_loc,
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unexpected_token_in_conditional */4,
+                      _2: curr_loc
+                    }
+                  });
       }
     } else {
       switch (curr_token.TAG | 0) {
         case /* FLOAT */1 :
             return token_op(calc, (function (e) {
-                          throw {
-                                MEL_EXN_ID: $$Error$2,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: /* Dir_type_float */1
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$2, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$2,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: /* Dir_type_float */1
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), {
                         TAG: /* Dir_float */1,
                         _0: Caml_format.caml_float_of_string(curr_token._0)
@@ -11346,22 +11445,24 @@ function directive_parse(token_with_comments, lexbuf) {
               case "undefined" :
                   break;
               default:
-                throw {
-                      MEL_EXN_ID: $$Error$2,
-                      _1: /* Unexpected_token_in_conditional */4,
-                      _2: curr_loc,
-                      Error: new Error()
-                    };
+                throw new Error($$Error$2, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$2,
+                            _1: /* Unexpected_token_in_conditional */4,
+                            _2: curr_loc
+                          }
+                        });
             }
             var t = token(undefined);
             var loc = curr(lexbuf);
             if (typeof t === "number") {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: /* Unexpected_token_in_conditional */4,
-                    _2: loc,
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: /* Unexpected_token_in_conditional */4,
+                          _2: loc
+                        }
+                      });
             }
             if (t.TAG === /* UIDENT */17) {
               var s = t._0;
@@ -11375,25 +11476,27 @@ function directive_parse(token_with_comments, lexbuf) {
                 return true;
               }
             }
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: /* Unexpected_token_in_conditional */4,
-                  _2: loc,
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: /* Unexpected_token_in_conditional */4,
+                        _2: loc
+                      }
+                    });
             break;
         case /* STRING */16 :
             return token_op(calc, (function (e) {
-                          throw {
-                                MEL_EXN_ID: $$Error$2,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: /* Dir_type_string */3
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$2, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$2,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: /* Dir_type_string */3
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), {
                         TAG: /* Dir_string */3,
                         _0: curr_token._0[0]
@@ -11406,24 +11509,26 @@ function directive_parse(token_with_comments, lexbuf) {
                             return value_v._0;
                           }
                           var ty = type_of_directive(value_v);
-                          throw {
-                                MEL_EXN_ID: $$Error$2,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: ty
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$2, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$2,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: ty
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), value_v);
         default:
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unexpected_token_in_conditional */4,
-                _2: curr_loc,
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unexpected_token_in_conditional */4,
+                      _2: curr_loc
+                    }
+                  });
       }
     }
   };
@@ -11446,12 +11551,13 @@ function directive_parse(token_with_comments, lexbuf) {
   if (match === 88) {
     return v;
   }
-  throw {
-        MEL_EXN_ID: $$Error$2,
-        _1: /* Expect_hash_then_in_conditional */5,
-        _2: curr(lexbuf),
-        Error: new Error()
-      };
+  throw new Error($$Error$2, {
+            cause: {
+              MEL_EXN_ID: $$Error$2,
+              _1: /* Expect_hash_then_in_conditional */5,
+              _2: curr(lexbuf)
+            }
+          });
 }
 
 function is_elif(i) {
@@ -11941,15 +12047,16 @@ function char_for_decimal_code(lexbuf, i) {
   if (Caml_obj.caml_notequal(comment_start_loc.contents, /* [] */0)) {
     return /* 'x' */120;
   }
-  throw {
-        MEL_EXN_ID: $$Error$2,
-        _1: {
-          TAG: /* Illegal_escape */1,
-          _0: Stdlib__Lexing.lexeme(lexbuf)
-        },
-        _2: curr(lexbuf),
-        Error: new Error()
-      };
+  throw new Error($$Error$2, {
+            cause: {
+              MEL_EXN_ID: $$Error$2,
+              _1: {
+                TAG: /* Illegal_escape */1,
+                _0: Stdlib__Lexing.lexeme(lexbuf)
+              },
+              _2: curr(lexbuf)
+            }
+          });
 }
 
 function char_for_hexadecimal_code(lexbuf, i) {
@@ -11977,15 +12084,16 @@ function cvt_int64_literal(s) {
 }
 
 function cvt_nativeint_literal(s) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "parsing/lexer.mll",
-          622,
-          30
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "parsing/lexer.mll",
+                622,
+                30
+              ]
+            }
+          });
 }
 
 function remove_underscores(s) {
@@ -12019,15 +12127,16 @@ function get_label_name(lexbuf) {
   var s = Stdlib__Lexing.lexeme(lexbuf);
   var name = Stdlib__String.sub(s, 1, s.length - 2 | 0);
   if (Stdlib__Hashtbl.mem(keyword_table, name)) {
-    throw {
-          MEL_EXN_ID: $$Error$2,
-          _1: {
-            TAG: /* Keyword_as_label */4,
-            _0: name
-          },
-          _2: curr(lexbuf),
-          Error: new Error()
-        };
+    throw new Error($$Error$2, {
+              cause: {
+                MEL_EXN_ID: $$Error$2,
+                _1: {
+                  TAG: /* Keyword_as_label */4,
+                  _0: name
+                },
+                _2: curr(lexbuf)
+              }
+            });
   }
   return name;
 }
@@ -12305,15 +12414,16 @@ function token(lexbuf) {
     switch (__ocaml_lex_state$1) {
       case 0 :
           if (!escaped_newlines.contents) {
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: {
-                    TAG: /* Illegal_character */0,
-                    _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
-                  },
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: {
+                          TAG: /* Illegal_character */0,
+                          _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
+                        },
+                        _2: curr(lexbuf)
+                      }
+                    });
           }
           update_loc(lexbuf, undefined, 1, false, 0);
           return token(lexbuf);
@@ -12369,7 +12479,9 @@ function token(lexbuf) {
                       _0: s
                     };
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
       case 11 :
           prerr_warning(curr(lexbuf), {
@@ -12404,17 +12516,20 @@ function token(lexbuf) {
           catch (raw_exn$1){
             var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
             if (exn$1.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "int"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "int"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
       case 15 :
           return {
@@ -12431,17 +12546,20 @@ function token(lexbuf) {
           catch (raw_exn$2){
             var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
             if (exn$2.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "int32"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "int32"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$2;
+            throw new Error(exn$2.MEL_EXN_ID, {
+                      cause: exn$2
+                    });
           }
       case 17 :
           try {
@@ -12453,17 +12571,20 @@ function token(lexbuf) {
           catch (raw_exn$3){
             var exn$3 = Caml_js_exceptions.internalToOCamlException(raw_exn$3);
             if (exn$3.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "int64"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "int64"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$3;
+            throw new Error(exn$3.MEL_EXN_ID, {
+                      cause: exn$3
+                    });
           }
       case 18 :
           try {
@@ -12475,17 +12596,20 @@ function token(lexbuf) {
           catch (raw_exn$4){
             var exn$4 = Caml_js_exceptions.internalToOCamlException(raw_exn$4);
             if (exn$4.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "nativeint"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "nativeint"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$4;
+            throw new Error(exn$4.MEL_EXN_ID, {
+                      cause: exn$4
+                    });
           }
       case 19 :
           reset_string_buffer(undefined);
@@ -12548,15 +12672,16 @@ function token(lexbuf) {
       case 26 :
           var l = Stdlib__Lexing.lexeme(lexbuf);
           var esc = Stdlib__String.sub(l, 1, l.length - 1 | 0);
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: {
-                  TAG: /* Illegal_escape */1,
-                  _0: esc
-                },
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: {
+                        TAG: /* Illegal_escape */1,
+                        _0: esc
+                      },
+                      _2: curr(lexbuf)
+                    }
+                  });
       case 27 :
           var match = with_comment_buffer(comment, lexbuf);
           return {
@@ -12765,29 +12890,32 @@ function token(lexbuf) {
             return /* EOF */25;
           }
           if (if_then_else.contents === /* Dir_if_true */0) {
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: /* Unterminated_if */2,
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: /* Unterminated_if */2,
+                        _2: curr(lexbuf)
+                      }
+                    });
           }
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unterminated_else */3,
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unterminated_else */3,
+                      _2: curr(lexbuf)
+                    }
+                  });
       case 91 :
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: {
-                  TAG: /* Illegal_character */0,
-                  _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
-                },
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: {
+                        TAG: /* Illegal_character */0,
+                        _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
+                      },
+                      _2: curr(lexbuf)
+                    }
+                  });
       default:
         Curry._1(lexbuf.refill_buff, lexbuf);
         ___ocaml_lex_state = __ocaml_lex_state$1;
@@ -12836,12 +12964,13 @@ function string(lexbuf) {
           return string(lexbuf);
       case 7 :
           is_in_string.contents = false;
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unterminated_string */0,
-                _2: string_start_loc.contents,
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unterminated_string */0,
+                      _2: string_start_loc.contents
+                    }
+                  });
       case 8 :
           store_string_char(Stdlib__Lexing.lexeme_char(lexbuf, 0));
           return string(lexbuf);
@@ -12869,12 +12998,13 @@ function __ocaml_lex_quoted_string_rec(delim, lexbuf, ___ocaml_lex_state) {
           continue ;
       case 1 :
           is_in_string.contents = false;
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unterminated_string */0,
-                _2: string_start_loc.contents,
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unterminated_string */0,
+                      _2: string_start_loc.contents
+                    }
+                  });
       case 2 :
           var edelim = Stdlib__Lexing.lexeme(lexbuf);
           var edelim$1 = Stdlib__String.sub(edelim, 1, edelim.length - 2 | 0);
@@ -12921,15 +13051,16 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
             comment_start_loc.contents = /* [] */0;
             return curr(lexbuf);
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "parsing/lexer.mll",
-                  992,
-                  16
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "parsing/lexer.mll",
+                        992,
+                        16
+                      ]
+                    }
+                  });
       case 2 :
           string_start_loc.contents = curr(lexbuf);
           store_string_char(/* '"' */34);
@@ -12943,36 +13074,44 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
               var match$1 = exn._1;
               if (typeof match$1 === "number") {
                 if (match$1) {
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
                 var match$2 = comment_start_loc.contents;
                 if (match$2) {
                   var start = Stdlib__List.hd(Stdlib__List.rev(comment_start_loc.contents));
                   comment_start_loc.contents = /* [] */0;
-                  throw {
-                        MEL_EXN_ID: $$Error$2,
-                        _1: {
-                          TAG: /* Unterminated_string_in_comment */3,
-                          _0: start,
-                          _1: exn._2
-                        },
-                        _2: match$2.hd,
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$2, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$2,
+                              _1: {
+                                TAG: /* Unterminated_string_in_comment */3,
+                                _0: start,
+                                _1: exn._2
+                              },
+                              _2: match$2.hd
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "parsing/lexer.mll",
-                        1006,
-                        18
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "parsing/lexer.mll",
+                              1006,
+                              18
+                            ]
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           is_in_string.contents = false;
           store_string_char(/* '"' */34);
@@ -12993,36 +13132,44 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
               var match$3 = exn$1._1;
               if (typeof match$3 === "number") {
                 if (match$3) {
-                  throw exn$1;
+                  throw new Error(exn$1.MEL_EXN_ID, {
+                            cause: exn$1
+                          });
                 }
                 var match$4 = comment_start_loc.contents;
                 if (match$4) {
                   var start$1 = Stdlib__List.hd(Stdlib__List.rev(comment_start_loc.contents));
                   comment_start_loc.contents = /* [] */0;
-                  throw {
-                        MEL_EXN_ID: $$Error$2,
-                        _1: {
-                          TAG: /* Unterminated_string_in_comment */3,
-                          _0: start$1,
-                          _1: exn$1._2
-                        },
-                        _2: match$4.hd,
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$2, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$2,
+                              _1: {
+                                TAG: /* Unterminated_string_in_comment */3,
+                                _0: start$1,
+                                _1: exn$1._2
+                              },
+                              _2: match$4.hd
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "parsing/lexer.mll",
-                        1026,
-                        18
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "parsing/lexer.mll",
+                              1026,
+                              18
+                            ]
+                          }
+                        });
               }
-              throw exn$1;
+              throw new Error(exn$1.MEL_EXN_ID, {
+                        cause: exn$1
+                      });
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
           is_in_string.contents = false;
           store_string_char(/* '|' */124);
@@ -13040,25 +13187,27 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
           if (match$5) {
             var start$2 = Stdlib__List.hd(Stdlib__List.rev(comment_start_loc.contents));
             comment_start_loc.contents = /* [] */0;
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: {
-                    TAG: /* Unterminated_comment */2,
-                    _0: start$2
-                  },
-                  _2: match$5.hd,
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: {
+                          TAG: /* Unterminated_comment */2,
+                          _0: start$2
+                        },
+                        _2: match$5.hd
+                      }
+                    });
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "parsing/lexer.mll",
-                  1056,
-                  16
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "parsing/lexer.mll",
+                        1056,
+                        16
+                      ]
+                    }
+                  });
       case 11 :
           update_loc(lexbuf, undefined, 1, false, 0);
           store_string(Stdlib__Lexing.lexeme(lexbuf));
@@ -13151,22 +13300,24 @@ function token$1(lexbuf) {
                   switch (match) {
                     case /* ELSE */23 :
                         if (if_then_else$1) {
-                          throw {
-                                MEL_EXN_ID: $$Error$2,
-                                _1: /* Unexpected_directive */6,
-                                _2: curr(lexbuf),
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$2, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$2,
+                                      _1: /* Unexpected_directive */6,
+                                      _2: curr(lexbuf)
+                                    }
+                                  });
                         }
                         break;
                     case /* END */24 :
                         if (if_then_else$1 >= 2) {
-                          throw {
-                                MEL_EXN_ID: $$Error$2,
-                                _1: /* Unexpected_directive */6,
-                                _2: curr(lexbuf),
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$2, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$2,
+                                      _1: /* Unexpected_directive */6,
+                                      _2: curr(lexbuf)
+                                    }
+                                  });
                         }
                         if_then_else.contents = /* Dir_out */2;
                         return Curry._1(cont, lexbuf);
@@ -13180,12 +13331,13 @@ function token$1(lexbuf) {
                             while(true) {
                               var token = token_with_comments(lexbuf);
                               if (Caml_obj.caml_equal(token, /* EOF */25)) {
-                                throw {
-                                      MEL_EXN_ID: $$Error$2,
-                                      _1: /* Unterminated_if */2,
-                                      _2: curr(lexbuf),
-                                      Error: new Error()
-                                    };
+                                throw new Error($$Error$2, {
+                                          cause: {
+                                            MEL_EXN_ID: $$Error$2,
+                                            _1: /* Unterminated_if */2,
+                                            _2: curr(lexbuf)
+                                          }
+                                        });
                               }
                               if (Caml_obj.caml_equal(token, /* SHARP */84) && at_bol(lexbuf)) {
                                 var token$1 = token_with_comments(lexbuf);
@@ -13200,12 +13352,13 @@ function token$1(lexbuf) {
                                     }
                                   }
                                   if (token$1 === 37) {
-                                    throw {
-                                          MEL_EXN_ID: $$Error$2,
-                                          _1: /* Unexpected_directive */6,
-                                          _2: curr(lexbuf),
-                                          Error: new Error()
-                                        };
+                                    throw new Error($$Error$2, {
+                                              cause: {
+                                                MEL_EXN_ID: $$Error$2,
+                                                _1: /* Unexpected_directive */6,
+                                                _2: curr(lexbuf)
+                                              }
+                                            });
                                   }
                                   
                                 }
@@ -13221,12 +13374,13 @@ function token$1(lexbuf) {
                             };
                           }
                         }
-                        throw {
-                              MEL_EXN_ID: $$Error$2,
-                              _1: /* Unexpected_directive */6,
-                              _2: curr(lexbuf),
-                              Error: new Error()
-                            };
+                        throw new Error($$Error$2, {
+                                  cause: {
+                                    MEL_EXN_ID: $$Error$2,
+                                    _1: /* Unexpected_directive */6,
+                                    _2: curr(lexbuf)
+                                  }
+                                });
                     default:
                       return Curry._1(look_ahead, match);
                   }
@@ -13238,12 +13392,13 @@ function token$1(lexbuf) {
                     return Curry._1(look_ahead, match);
                   }
                   if (if_then_else$1) {
-                    throw {
-                          MEL_EXN_ID: $$Error$2,
-                          _1: /* Unexpected_directive */6,
-                          _2: curr(lexbuf),
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$2, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$2,
+                                _1: /* Unexpected_directive */6,
+                                _2: curr(lexbuf)
+                              }
+                            });
                   }
                   
                 }
@@ -13255,12 +13410,13 @@ function token$1(lexbuf) {
                   var else_seen = _else_seen;
                   var token$2 = token_with_comments(lexbuf);
                   if (Caml_obj.caml_equal(token$2, /* EOF */25)) {
-                    throw {
-                          MEL_EXN_ID: $$Error$2,
-                          _1: /* Unterminated_else */3,
-                          _2: curr(lexbuf),
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$2, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$2,
+                                _1: /* Unterminated_else */3,
+                                _2: curr(lexbuf)
+                              }
+                            });
                   }
                   if (Caml_obj.caml_equal(token$2, /* SHARP */84) && at_bol(lexbuf)) {
                     var token$3 = token_with_comments(lexbuf);
@@ -13271,33 +13427,36 @@ function token$1(lexbuf) {
                           return Curry._1(cont, lexbuf);
                         }
                         if (else_seen) {
-                          throw {
-                                MEL_EXN_ID: $$Error$2,
-                                _1: /* Unexpected_directive */6,
-                                _2: curr(lexbuf),
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$2, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$2,
+                                      _1: /* Unexpected_directive */6,
+                                      _2: curr(lexbuf)
+                                    }
+                                  });
                         }
                         _else_seen = true;
                         continue ;
                       }
                       if (token$3 === 37) {
-                        throw {
-                              MEL_EXN_ID: $$Error$2,
-                              _1: /* Unexpected_directive */6,
-                              _2: curr(lexbuf),
-                              Error: new Error()
-                            };
+                        throw new Error($$Error$2, {
+                                  cause: {
+                                    MEL_EXN_ID: $$Error$2,
+                                    _1: /* Unexpected_directive */6,
+                                    _2: curr(lexbuf)
+                                  }
+                                });
                       }
                       
                     }
                     if (else_seen && is_elif(token$3)) {
-                      throw {
-                            MEL_EXN_ID: $$Error$2,
-                            _1: /* Unexpected_directive */6,
-                            _2: curr(lexbuf),
-                            Error: new Error()
-                          };
+                      throw new Error($$Error$2, {
+                                cause: {
+                                  MEL_EXN_ID: $$Error$2,
+                                  _1: /* Unexpected_directive */6,
+                                  _2: curr(lexbuf)
+                                }
+                              });
                     }
                     continue ;
                   }
@@ -13433,7 +13592,9 @@ function skip_phrase(lexbuf) {
           if (tmp === /* Unterminated_string */0) {
             continue ;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         } else {
           switch (tmp.TAG | 0) {
             case /* Illegal_character */0 :
@@ -13441,11 +13602,15 @@ function skip_phrase(lexbuf) {
             case /* Unterminated_string_in_comment */3 :
                 continue ;
             default:
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
           }
         }
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
   };
@@ -13473,26 +13638,40 @@ function wrap(parsing_fun, lexbuf) {
     if (err.MEL_EXN_ID === $$Error$2) {
       var tmp = err._1;
       if (typeof tmp === "number") {
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       if (tmp.TAG === /* Illegal_character */0) {
         if (input_name.contents === "//toplevel//") {
           skip_phrase(lexbuf);
-          throw err;
+          throw new Error(err.MEL_EXN_ID, {
+                    cause: err
+                  });
         }
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
-      throw err;
+      throw new Error(err.MEL_EXN_ID, {
+                cause: err
+              });
     } else {
       if (err.MEL_EXN_ID === $$Error$1) {
         if (input_name.contents === "//toplevel//") {
           maybe_skip_phrase(lexbuf);
-          throw err;
+          throw new Error(err.MEL_EXN_ID, {
+                    cause: err
+                  });
         }
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       if (err.MEL_EXN_ID !== Stdlib__Parsing.Parse_error && err.MEL_EXN_ID !== Escape_error) {
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       
     }
@@ -13500,14 +13679,15 @@ function wrap(parsing_fun, lexbuf) {
     if (input_name.contents === "//toplevel//") {
       maybe_skip_phrase(lexbuf);
     }
-    throw {
-          MEL_EXN_ID: $$Error$1,
-          _1: {
-            TAG: /* Other */5,
-            _0: loc
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$1, {
+              cause: {
+                MEL_EXN_ID: $$Error$1,
+                _1: {
+                  TAG: /* Other */5,
+                  _0: loc
+                }
+              }
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/ocaml_proto_test.js b/jscomp/test/dist/jscomp/test/ocaml_proto_test.js
index e56c09a50b..791a997fac 100644
--- a/jscomp/test/dist/jscomp/test/ocaml_proto_test.js
+++ b/jscomp/test/dist/jscomp/test/ocaml_proto_test.js
@@ -199,7 +199,9 @@ function file_option(file_options, name) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return x;
 }
@@ -222,7 +224,9 @@ function rev_split_by_char(c, s) {
                 tl: l
               };
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   return loop(0, /* [] */0);
@@ -239,11 +243,12 @@ function pop_last(param) {
       return /* [] */0;
     }
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "Invalid argument [] for pop_last",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "Invalid argument [] for pop_last"
+            }
+          });
 }
 
 function apply_until(f, _param) {
@@ -743,44 +748,47 @@ Stdlib__Printexc.register_printer(function (exn) {
     });
 
 function invalid_default_value(field_name, info, param) {
-  throw {
-        MEL_EXN_ID: Compilation_error,
-        _1: {
-          TAG: /* Invalid_default_value */2,
-          _0: {
-            field_name: field_name,
-            info: info
-          }
-        },
-        Error: new Error()
-      };
+  throw new Error(Compilation_error, {
+            cause: {
+              MEL_EXN_ID: Compilation_error,
+              _1: {
+                TAG: /* Invalid_default_value */2,
+                _0: {
+                  field_name: field_name,
+                  info: info
+                }
+              }
+            }
+          });
 }
 
 function unsupported_field_type(field_name, field_type, backend_name, param) {
-  throw {
-        MEL_EXN_ID: Compilation_error,
-        _1: {
-          TAG: /* Unsupported_field_type */3,
-          _0: {
-            field_name: field_name,
-            field_type: field_type,
-            backend_name: backend_name
-          }
-        },
-        Error: new Error()
-      };
+  throw new Error(Compilation_error, {
+            cause: {
+              MEL_EXN_ID: Compilation_error,
+              _1: {
+                TAG: /* Unsupported_field_type */3,
+                _0: {
+                  field_name: field_name,
+                  field_type: field_type,
+                  backend_name: backend_name
+                }
+              }
+            }
+          });
 }
 
 function invalid_enum_specification(enum_name, loc) {
-  throw {
-        MEL_EXN_ID: Compilation_error,
-        _1: {
-          TAG: /* Invalid_enum_specification */10,
-          _0: enum_name,
-          _1: loc
-        },
-        Error: new Error()
-      };
+  throw new Error(Compilation_error, {
+            cause: {
+              MEL_EXN_ID: Compilation_error,
+              _1: {
+                TAG: /* Invalid_enum_specification */10,
+                _0: enum_name,
+                _1: loc
+              }
+            }
+          });
 }
 
 var yytransl_const = [
@@ -825,11 +833,12 @@ var yytransl_block = [
 
 var yyact = [
   (function (param) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "parser",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "parser"
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -951,14 +960,15 @@ var yyact = [
       Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       Stdlib__Parsing.peek_val(__caml_parser_env, 0);
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Invalid_import_qualifier */5,
-              _0: _1
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Invalid_import_qualifier */5,
+                    _0: _1
+                  }
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -1028,11 +1038,12 @@ var yyact = [
             };
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: /* Syntax_error */0,
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: /* Syntax_error */0
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 3);
@@ -1112,14 +1123,15 @@ var yyact = [
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 3);
       Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       Stdlib__Parsing.peek_val(__caml_parser_env, 0);
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Missing_one_of_name */12,
-              _0: _1
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Missing_one_of_name */12,
+                    _0: _1
+                  }
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return /* [] */0;
@@ -1187,28 +1199,30 @@ var yyact = [
       Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       Stdlib__Parsing.peek_val(__caml_parser_env, 0);
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Missing_field_label */14,
-              _0: _1[0]
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Missing_field_label */14,
+                    _0: _1[0]
+                  }
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 4);
       Stdlib__Parsing.peek_val(__caml_parser_env, 3);
       Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       Stdlib__Parsing.peek_val(__caml_parser_env, 0);
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Missing_field_label */14,
-              _0: _1[0]
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Missing_field_label */14,
+                    _0: _1[0]
+                  }
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 0)[1];
@@ -1274,14 +1288,15 @@ var yyact = [
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Invalid_field_label */13,
-              _0: _1[0]
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Invalid_field_label */13,
+                    _0: _1[0]
+                  }
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -1424,15 +1439,16 @@ var yyact = [
       Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       var enum_value = _1[1];
       var loc = _1[0];
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Missing_semicolon_for_enum_value */9,
-              _0: enum_value,
-              _1: loc
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Missing_semicolon_for_enum_value */9,
+                    _0: enum_value,
+                    _1: loc
+                  }
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 3);
@@ -1464,88 +1480,100 @@ var yyact = [
       Stdlib__Parsing.peek_val(__caml_parser_env, 1);
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     })
 ];
 
@@ -1831,11 +1859,12 @@ function lexer(lexbuf) {
                     },
                     _1: "Unknown character found %s"
                   }), Stdlib__Lexing.lexeme(lexbuf));
-          throw {
-                MEL_EXN_ID: "Failure",
-                _1: s$1,
-                Error: new Error()
-              };
+          throw new Error("Failure", {
+                    cause: {
+                      MEL_EXN_ID: "Failure",
+                      _1: s$1
+                    }
+                  });
       default:
         Curry._1(lexbuf.refill_buff, lexbuf);
         ___ocaml_lex_state = __ocaml_lex_state$1;
@@ -2132,11 +2161,12 @@ function runtime_function(param) {
               case /* Bt_int64 */4 :
               case /* Bt_bytes */5 :
               case /* Bt_bool */6 :
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "Invalid encoding/OCaml type combination",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "Invalid encoding/OCaml type combination"
+                            }
+                          });
               
             }
         case /* Pk_bits64 */1 :
@@ -2151,11 +2181,12 @@ function runtime_function(param) {
               case /* Bt_int32 */3 :
               case /* Bt_bytes */5 :
               case /* Bt_bool */6 :
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "Invalid encoding/OCaml type combination",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "Invalid encoding/OCaml type combination"
+                            }
+                          });
               
             }
         case /* Pk_bytes */2 :
@@ -2166,11 +2197,12 @@ function runtime_function(param) {
             if (!match$2) {
               return "Pbrt.Decoder.string";
             }
-            throw {
-                  MEL_EXN_ID: "Failure",
-                  _1: "Invalid encoding/OCaml type combination",
-                  Error: new Error()
-                };
+            throw new Error("Failure", {
+                      cause: {
+                        MEL_EXN_ID: "Failure",
+                        _1: "Invalid encoding/OCaml type combination"
+                      }
+                    });
         
       }
     } else if (match$1._0) {
@@ -2185,11 +2217,12 @@ function runtime_function(param) {
         case /* Bt_float */1 :
         case /* Bt_bytes */5 :
         case /* Bt_bool */6 :
-            throw {
-                  MEL_EXN_ID: "Failure",
-                  _1: "Invalid encoding/OCaml type combination",
-                  Error: new Error()
-                };
+            throw new Error("Failure", {
+                      cause: {
+                        MEL_EXN_ID: "Failure",
+                        _1: "Invalid encoding/OCaml type combination"
+                      }
+                    });
         
       }
     } else {
@@ -2203,11 +2236,12 @@ function runtime_function(param) {
         case /* Bt_string */0 :
         case /* Bt_float */1 :
         case /* Bt_bytes */5 :
-            throw {
-                  MEL_EXN_ID: "Failure",
-                  _1: "Invalid encoding/OCaml type combination",
-                  Error: new Error()
-                };
+            throw new Error("Failure", {
+                      cause: {
+                        MEL_EXN_ID: "Failure",
+                        _1: "Invalid encoding/OCaml type combination"
+                      }
+                    });
         case /* Bt_bool */6 :
             return "Pbrt.Decoder.bool";
         
@@ -2229,11 +2263,12 @@ function runtime_function(param) {
               case /* Bt_int64 */4 :
               case /* Bt_bytes */5 :
               case /* Bt_bool */6 :
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "Invalid encoding/OCaml type combination",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "Invalid encoding/OCaml type combination"
+                            }
+                          });
               
             }
         case /* Pk_bits64 */1 :
@@ -2248,11 +2283,12 @@ function runtime_function(param) {
               case /* Bt_int32 */3 :
               case /* Bt_bytes */5 :
               case /* Bt_bool */6 :
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "Invalid encoding/OCaml type combination",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "Invalid encoding/OCaml type combination"
+                            }
+                          });
               
             }
         case /* Pk_bytes */2 :
@@ -2263,11 +2299,12 @@ function runtime_function(param) {
             if (!match$4) {
               return "Pbrt.Encoder.string";
             }
-            throw {
-                  MEL_EXN_ID: "Failure",
-                  _1: "Invalid encoding/OCaml type combination",
-                  Error: new Error()
-                };
+            throw new Error("Failure", {
+                      cause: {
+                        MEL_EXN_ID: "Failure",
+                        _1: "Invalid encoding/OCaml type combination"
+                      }
+                    });
         
       }
     } else if (match$3._0) {
@@ -2282,11 +2319,12 @@ function runtime_function(param) {
         case /* Bt_float */1 :
         case /* Bt_bytes */5 :
         case /* Bt_bool */6 :
-            throw {
-                  MEL_EXN_ID: "Failure",
-                  _1: "Invalid encoding/OCaml type combination",
-                  Error: new Error()
-                };
+            throw new Error("Failure", {
+                      cause: {
+                        MEL_EXN_ID: "Failure",
+                        _1: "Invalid encoding/OCaml type combination"
+                      }
+                    });
         
       }
     } else {
@@ -2300,22 +2338,24 @@ function runtime_function(param) {
         case /* Bt_string */0 :
         case /* Bt_float */1 :
         case /* Bt_bytes */5 :
-            throw {
-                  MEL_EXN_ID: "Failure",
-                  _1: "Invalid encoding/OCaml type combination",
-                  Error: new Error()
-                };
+            throw new Error("Failure", {
+                      cause: {
+                        MEL_EXN_ID: "Failure",
+                        _1: "Invalid encoding/OCaml type combination"
+                      }
+                    });
         case /* Bt_bool */6 :
             return "Pbrt.Encoder.bool";
         
       }
     }
   } else {
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "Invalid encoding/OCaml type combination",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "Invalid encoding/OCaml type combination"
+              }
+            });
   }
 }
 
@@ -3903,17 +3943,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -3935,17 +3977,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add(x, data, m) {
@@ -4003,10 +4047,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -4048,17 +4093,19 @@ function min_value(param) {
     if (y !== undefined) {
       return Caml_option.some(Caml_obj.caml_min(Caml_option.valFromOption(x), Caml_option.valFromOption(y)));
     }
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "min_value error",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "min_value error"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "min_value error",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "min_value error"
+            }
+          });
 }
 
 function eq_value(param) {
@@ -4068,17 +4115,19 @@ function eq_value(param) {
     if (y !== undefined) {
       return Caml_obj.caml_equal(Caml_option.valFromOption(x), Caml_option.valFromOption(y));
     }
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "eq_value error",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "eq_value error"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "eq_value error",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "eq_value error"
+            }
+          });
 }
 
 function string_of_option(f, param) {
@@ -4389,7 +4438,9 @@ function find_field_option(field_options, option_name) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return Caml_option.some(x);
 }
@@ -4466,14 +4517,15 @@ function unresolved_of_string(s) {
             from_root: Caml_string.get(s, 0) === /* '.' */46
           };
   }
-  throw {
-        MEL_EXN_ID: Compilation_error,
-        _1: {
-          TAG: /* Programatic_error */4,
-          _0: /* Invalid_string_split */0
-        },
-        Error: new Error()
-      };
+  throw new Error(Compilation_error, {
+            cause: {
+              MEL_EXN_ID: Compilation_error,
+              _1: {
+                TAG: /* Programatic_error */4,
+                _0: /* Invalid_string_split */0
+              }
+            }
+          });
 }
 
 function field_type_of_string(s) {
@@ -4625,7 +4677,9 @@ function get_default(field_name, field_options, field_type) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return Caml_option.some(constant);
 }
@@ -4669,7 +4723,9 @@ function not_found(f) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4684,10 +4740,11 @@ function list_assoc2(x, _param) {
       _param = param.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -4819,18 +4876,19 @@ function compile_message_p1(file_name, file_options, message_scope, param) {
             };
     } else {
       var previous_field_name = "";
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Duplicated_field_number */1,
-              _0: {
-                field_name: name,
-                previous_field_name: previous_field_name,
-                message_name: message_name
-              }
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Duplicated_field_number */1,
+                    _0: {
+                      field_name: name,
+                      previous_field_name: previous_field_name,
+                      message_name: message_name
+                    }
+                  }
+                }
+              });
     }
   };
   Stdlib__List.fold_left((function (number_index, param) {
@@ -4955,14 +5013,15 @@ function compile_message_p2(types, param, message) {
       if (typeof field_type === "number") {
         return field_type;
       }
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Programatic_error */4,
-              _0: /* Unexpected_field_type */1
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Programatic_error */4,
+                    _0: /* Unexpected_field_type */1
+                  }
+                }
+              });
     }
     var unresolved = field_type._0;
     var type_name = unresolved.type_name;
@@ -5029,7 +5088,9 @@ function compile_message_p2(types, param, message) {
               if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                 return ;
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }), search_scopes$1);
     if (id !== undefined) {
@@ -5037,18 +5098,19 @@ function compile_message_p2(types, param, message) {
               _0: id
             };
     } else {
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Unresolved_type */0,
-              _0: {
-                field_name: field_name,
-                type_: type_name,
-                message_name: message_name
-              }
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Unresolved_type */0,
+                    _0: {
+                      field_name: field_name,
+                      type_: type_name,
+                      message_name: message_name
+                    }
+                  }
+                }
+              });
     }
   };
   var message_body = Stdlib__List.fold_left((function (message_body, param) {
@@ -6441,15 +6503,16 @@ function record_field_default_info(record_field) {
                       _1: "%s (%s)"
                     }), vc_constructor, dfvft(vc_field_type._0, undefined)) : vc_constructor;
         } else {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "codegen_default.ml",
-                  74,
-                  15
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "codegen_default.ml",
+                        74,
+                        15
+                      ]
+                    }
+                  });
         }
         break;
     
@@ -6708,11 +6771,12 @@ function gen_default_variant(and_, param, sc) {
                         _1: "%s default_%s () : %s = %s (%s)"
                       }), decl, v_name, v_name, vc_constructor, default_value));
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "programmatic TODO error",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "programmatic TODO error"
+            }
+          });
 }
 
 function gen_default_const_variant(and_, param, sc) {
@@ -6722,11 +6786,12 @@ function gen_default_const_variant(and_, param, sc) {
   if (cv_constructors) {
     first_constructor_name = cv_constructors.hd[0];
   } else {
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "programmatic TODO error",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "programmatic TODO error"
+              }
+            });
   }
   line$1(sc, Curry._4(Stdlib__Printf.sprintf(/* Format */{
                 _0: {
@@ -7083,16 +7148,19 @@ function module_of_file_name(file_name) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Invalid_file_name */6,
-              _0: file_name$1
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Invalid_file_name */6,
+                    _0: file_name$1
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return constructor_name(Stdlib__String.sub(file_name$1, 0, dot_index) + "_pb");
 }
@@ -7113,11 +7181,12 @@ function type_name(message_scope, name) {
       return fix_ocaml_keyword_conflict(all_names$2.hd);
     }
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "Programmatic error",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "Programmatic error"
+            }
+          });
 }
 
 function encoding_info_of_field_type(all_types, field_type) {
@@ -7169,14 +7238,15 @@ function encoding_of_field(all_types, field) {
       packed = match._0;
     } else {
       var field_name$1 = field_name(field);
-      throw {
-            MEL_EXN_ID: Compilation_error,
-            _1: {
-              TAG: /* Invalid_packed_option */8,
-              _0: field_name$1
-            },
-            Error: new Error()
-          };
+      throw new Error(Compilation_error, {
+                cause: {
+                  MEL_EXN_ID: Compilation_error,
+                  _1: {
+                    TAG: /* Invalid_packed_option */8,
+                    _0: field_name$1
+                  }
+                }
+              });
     }
   } else {
     packed = false;
@@ -7219,16 +7289,19 @@ function compile_field_type(field_name, all_types, file_options, field_options,
     catch (raw_exn){
       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-        throw {
-              MEL_EXN_ID: Compilation_error,
-              _1: {
-                TAG: /* Programatic_error */4,
-                _0: /* No_type_found_for_id */2
-              },
-              Error: new Error()
-            };
+        throw new Error(Compilation_error, {
+                  cause: {
+                    MEL_EXN_ID: Compilation_error,
+                    _1: {
+                      TAG: /* Programatic_error */4,
+                      _0: /* No_type_found_for_id */2
+                    }
+                  }
+                });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
     if (is_empty_message(t)) {
       return /* Ft_unit */0;
@@ -7320,14 +7393,15 @@ function is_mutable(field_name, field_options) {
   if (match.TAG === /* Constant_bool */1) {
     return match._0;
   }
-  throw {
-        MEL_EXN_ID: Compilation_error,
-        _1: {
-          TAG: /* Invalid_mutable_option */11,
-          _0: field_name
-        },
-        Error: new Error()
-      };
+  throw new Error(Compilation_error, {
+            cause: {
+              MEL_EXN_ID: Compilation_error,
+              _1: {
+                TAG: /* Invalid_mutable_option */11,
+                _0: field_name
+              }
+            }
+          });
 }
 
 function ocaml_container(field_options) {
@@ -7407,7 +7481,9 @@ function compile(proto_definition) {
   }
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
-    throw add_loc(from_lexbuf(lexbuf), exn);
+    throw new Error(add_loc(from_lexbuf(lexbuf), exn).MEL_EXN_ID, {
+              cause: add_loc(from_lexbuf(lexbuf), exn)
+            });
   }
   var all_pbtt_msgs = compile_proto_p1("tmp.proto", proto);
   var all_pbtt_msgs$1 = Stdlib__List.map((function (param) {
@@ -7527,11 +7603,12 @@ function compile(proto_definition) {
                                             if (match$2 === "repeated_field") {
                                               repeated_type = /* Rt_repeated_field */1;
                                             } else {
-                                              throw {
-                                                    MEL_EXN_ID: "Failure",
-                                                    _1: "Invalid ocaml_container attribute value",
-                                                    Error: new Error()
-                                                  };
+                                              throw new Error("Failure", {
+                                                        cause: {
+                                                          MEL_EXN_ID: "Failure",
+                                                          _1: "Invalid ocaml_container attribute value"
+                                                        }
+                                                      });
                                             }
                                           } else {
                                             repeated_type = /* Rt_list */0;
@@ -7617,20 +7694,22 @@ function compile(proto_definition) {
                                         var key_pk = encoding_info_of_field_type(all_pbtt_msgs$1, map_key_type);
                                         var key_type$1;
                                         if (typeof key_type === "number") {
-                                          throw {
-                                                MEL_EXN_ID: "Failure",
-                                                _1: "Only Basic Types are supported for map keys",
-                                                Error: new Error()
-                                              };
+                                          throw new Error("Failure", {
+                                                    cause: {
+                                                      MEL_EXN_ID: "Failure",
+                                                      _1: "Only Basic Types are supported for map keys"
+                                                    }
+                                                  });
                                         }
                                         if (key_type.TAG === /* Ft_basic_type */0) {
                                           key_type$1 = key_type._0;
                                         } else {
-                                          throw {
-                                                MEL_EXN_ID: "Failure",
-                                                _1: "Only Basic Types are supported for map keys",
-                                                Error: new Error()
-                                              };
+                                          throw new Error("Failure", {
+                                                    cause: {
+                                                      MEL_EXN_ID: "Failure",
+                                                      _1: "Only Basic Types are supported for map keys"
+                                                    }
+                                                  });
                                         }
                                         var value_type = compile_field_type(Curry._1(Stdlib__Printf.sprintf(/* Format */{
                                                       _0: {
@@ -7651,11 +7730,12 @@ function compile(proto_definition) {
                                           if (match$3 === "hashtbl") {
                                             associative_type = /* At_hashtable */1;
                                           } else {
-                                            throw {
-                                                  MEL_EXN_ID: "Failure",
-                                                  _1: "Invalid ocaml_container attribute value for map",
-                                                  Error: new Error()
-                                                };
+                                            throw new Error("Failure", {
+                                                      cause: {
+                                                        MEL_EXN_ID: "Failure",
+                                                        _1: "Invalid ocaml_container attribute value for map"
+                                                      }
+                                                    });
                                           }
                                         } else {
                                           associative_type = /* At_list */0;
diff --git a/jscomp/test/dist/jscomp/test/ocaml_re_test.js b/jscomp/test/dist/jscomp/test/ocaml_re_test.js
index a459542f8b..c063d74d52 100644
--- a/jscomp/test/dist/jscomp/test/ocaml_re_test.js
+++ b/jscomp/test/dist/jscomp/test/ocaml_re_test.js
@@ -333,17 +333,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -365,17 +367,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add(x, data, m) {
@@ -433,10 +437,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -539,17 +544,19 @@ function bal$1(l, v, r) {
       if (lr) {
         return create$1(create$1(ll, lv, lr.l), lr.v, create$1(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -569,17 +576,19 @@ function bal$1(l, v, r) {
     if (rl) {
       return create$1(create$1(l, v, rl.l), rl.v, create$1(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$1(x, t) {
@@ -1091,15 +1100,16 @@ function split_at_match_rec(_l$p, _param) {
         
       }
     } else {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "re_automata.ml",
-              429,
-              21
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "re_automata.ml",
+                    429,
+                    21
+                  ]
+                }
+              });
     }
   };
 }
@@ -1539,7 +1549,9 @@ function find_state(re, desc) {
       Curry._3(Re_automata_State.Table.add, re.states, desc, st);
       return st;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -1620,7 +1632,9 @@ function $$final(info, st, cat) {
       };
       return res;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -1641,7 +1655,9 @@ function find_initial_state(re, cat) {
       };
       return st;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -1751,7 +1767,9 @@ function trans_set(cache, cm, s) {
       cache.contents = Curry._3(add, v, l, cache.contents);
       return l;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -1891,15 +1909,16 @@ function colorize(c, regexp) {
               _regexp = regexp._1;
               continue ;
           default:
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "re.ml",
-                    502,
-                    35
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "re.ml",
+                          502,
+                          35
+                        ]
+                      }
+                    });
         }
       }
     };
@@ -2487,15 +2506,16 @@ function translate(ids, kind, _ign_group, ign_case, _greedy, pos, cache, c, _par
                     match$5[1]
                   ];
         default:
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "re.ml",
-                  714,
-                  4
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "re.ml",
+                        714,
+                        4
+                      ]
+                    }
+                  });
       }
     }
   };
@@ -2528,28 +2548,30 @@ function case_insens(s) {
 
 function as_set(param) {
   if (typeof param === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "re.ml",
-            747,
-            13
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "re.ml",
+                  747,
+                  13
+                ]
+              }
+            });
   }
   if (param.TAG === /* Set */0) {
     return param._0;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "re.ml",
-          747,
-          13
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "re.ml",
+                747,
+                13
+              ]
+            }
+          });
 }
 
 function handle_case(_ign_case, _r) {
@@ -2770,18 +2792,20 @@ var epsilon = {
 
 function repn(r, i, j) {
   if (i < 0) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Re.repn",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Re.repn"
+              }
+            });
   }
   if (j !== undefined && j < i) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Re.repn",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Re.repn"
+              }
+            });
   }
   return {
           TAG: /* Repeat */3,
@@ -2810,11 +2834,12 @@ function compl(l) {
   if (is_charset(r)) {
     return r;
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Re.compl",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Re.compl"
+            }
+          });
 }
 
 var any = {
@@ -3164,11 +3189,12 @@ function exec_internal(name, posOpt, lenOpt, groups, re, s) {
   var pos = posOpt !== undefined ? posOpt : 0;
   var len = lenOpt !== undefined ? lenOpt : -1;
   if (pos < 0 || len < -1 || (pos + len | 0) > s.length) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: name,
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: name
+              }
+            });
   }
   var partial = false;
   var slen = s.length;
@@ -3233,17 +3259,19 @@ function exec_internal(name, posOpt, lenOpt, groups, re, s) {
 
 function offset$1(t, i) {
   if (((i << 1) + 1 | 0) >= t.marks.length) {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   var m1 = Caml_array.get(t.marks, (i << 1));
   if (m1 === -1) {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   var p1 = Caml_array.get(t.gpos, m1) - 1 | 0;
   var p2 = Caml_array.get(t.gpos, Caml_array.get(t.marks, (i << 1) + 1 | 0)) - 1 | 0;
@@ -3293,11 +3321,12 @@ function posix_class_of_string(class_) {
         return xdigit;
     default:
       var s = "Invalid pcre class: " + class_;
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: s,
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: s
+                }
+              });
   }
 }
 
@@ -3326,18 +3355,20 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
       for(var j = 0; j < len; ++j){
         try {
           if (Caml_string.get(s$p, j) !== Caml_string.get(s, i.contents + j | 0)) {
-            throw {
-                  MEL_EXN_ID: Stdlib.Exit,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Exit, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Exit
+                      }
+                    });
           }
           
         }
         catch (exn){
-          throw {
-                MEL_EXN_ID: Stdlib.Exit,
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Exit, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Exit
+                    }
+                  });
         }
       }
       i.contents = i.contents + len | 0;
@@ -3348,7 +3379,9 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
       if (exn$1.MEL_EXN_ID === Stdlib.Exit) {
         return false;
       }
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
   };
   var get = function (param) {
@@ -3496,10 +3529,11 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
         if (accept(/* ':' */58)) {
           var r = regexp$p(branch$p(/* [] */0));
           if (!accept(/* ')' */41)) {
-            throw {
-                  MEL_EXN_ID: Parse_error,
-                  Error: new Error()
-                };
+            throw new Error(Parse_error, {
+                      cause: {
+                        MEL_EXN_ID: Parse_error
+                      }
+                    });
           }
           return r;
         }
@@ -3514,17 +3548,19 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
             continue ;
           };
         }
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       var r$1 = regexp$p(branch$p(/* [] */0));
       if (!accept(/* ')' */41)) {
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       return {
               TAG: /* Group */6,
@@ -3556,10 +3592,11 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
     }
     if (accept(/* '\\' */92)) {
       if (i.contents === l) {
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       var c = get(undefined);
       switch (c) {
@@ -3573,10 +3610,11 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
         case 55 :
         case 56 :
         case 57 :
-            throw {
-                  MEL_EXN_ID: Not_supported,
-                  Error: new Error()
-                };
+            throw new Error(Not_supported, {
+                      cause: {
+                        MEL_EXN_ID: Not_supported
+                      }
+                    });
         case 65 :
             return /* Beg_of_str */5;
         case 66 :
@@ -3698,10 +3736,11 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
         case 118 :
         case 120 :
         case 121 :
-            throw {
-                  MEL_EXN_ID: Parse_error,
-                  Error: new Error()
-                };
+            throw new Error(Parse_error, {
+                      cause: {
+                        MEL_EXN_ID: Parse_error
+                      }
+                    });
         case 122 :
             return /* End_of_str */6;
         default:
@@ -3712,10 +3751,11 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
       }
     } else {
       if (i.contents === l) {
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       var c$1 = get(undefined);
       if (c$1 >= 64) {
@@ -3726,22 +3766,25 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
                     _0: single(c$1)
                   };
           }
-          throw {
-                MEL_EXN_ID: Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Parse_error
+                    }
+                  });
         }
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       if (c$1 >= 44) {
         if (c$1 >= 63) {
-          throw {
-                MEL_EXN_ID: Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Parse_error
+                    }
+                  });
         }
         return {
                 TAG: /* Set */0,
@@ -3749,10 +3792,11 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
               };
       }
       if (c$1 >= 42) {
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       return {
               TAG: /* Set */0,
@@ -3782,10 +3826,11 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
         }
         var i$p = Math.imul(10, i$1) + (d$1 - /* '0' */48 | 0) | 0;
         if (i$p < i$1) {
-          throw {
-                MEL_EXN_ID: Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Parse_error
+                    }
+                  });
         }
         _i = i$p;
         continue ;
@@ -3794,18 +3839,20 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
   };
   var $$char = function (param) {
     if (i.contents === l) {
-      throw {
-            MEL_EXN_ID: Parse_error,
-            Error: new Error()
-          };
+      throw new Error(Parse_error, {
+                cause: {
+                  MEL_EXN_ID: Parse_error
+                }
+              });
     }
     var c = get(undefined);
     if (c === /* '[' */91) {
       if (accept(/* '=' */61)) {
-        throw {
-              MEL_EXN_ID: Not_supported,
-              Error: new Error()
-            };
+        throw new Error(Not_supported, {
+                  cause: {
+                    MEL_EXN_ID: Not_supported
+                  }
+                });
       }
       if (accept(/* ':' */58)) {
         var compl$1 = accept(/* '^' */94);
@@ -3855,18 +3902,22 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
         catch (raw_exn){
           var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-            throw {
-                  MEL_EXN_ID: Parse_error,
-                  Error: new Error()
-                };
+            throw new Error(Parse_error, {
+                      cause: {
+                        MEL_EXN_ID: Parse_error
+                      }
+                    });
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
         if (!accept_s(":]")) {
-          throw {
-                MEL_EXN_ID: Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Parse_error
+                    }
+                  });
         }
         var posix_class = posix_class_of_string(cls);
         var re = compl$1 ? compl({
@@ -3885,23 +3936,26 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
               };
       }
       if (i.contents === l) {
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       var c$1 = get(undefined);
       if (!accept(/* '.' */46)) {
-        throw {
-              MEL_EXN_ID: Not_supported,
-              Error: new Error()
-            };
+        throw new Error(Not_supported, {
+                  cause: {
+                    MEL_EXN_ID: Not_supported
+                  }
+                });
       }
       if (!accept(/* ']' */93)) {
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       return {
               NAME: "Char",
@@ -4068,18 +4122,20 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
         case 120 :
         case 121 :
         case 122 :
-            throw {
-                  MEL_EXN_ID: Parse_error,
-                  Error: new Error()
-                };
+            throw new Error(Parse_error, {
+                      cause: {
+                        MEL_EXN_ID: Parse_error
+                      }
+                    });
         
       }
     } else {
       if (c$2 >= 48) {
-        throw {
-              MEL_EXN_ID: Not_supported,
-              Error: new Error()
-            };
+        throw new Error(Not_supported, {
+                  cause: {
+                    MEL_EXN_ID: Not_supported
+                  }
+                });
       }
       return {
               NAME: "Char",
@@ -4105,16 +4161,18 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
     if (i$1 !== undefined) {
       var j = accept(/* ',' */44) ? integer(undefined) : i$1;
       if (!accept(/* '}' */125)) {
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       if (j !== undefined && j < i$1) {
-        throw {
-              MEL_EXN_ID: Parse_error,
-              Error: new Error()
-            };
+        throw new Error(Parse_error, {
+                  cause: {
+                    MEL_EXN_ID: Parse_error
+                  }
+                });
       }
       return greedy_mod(repn(r, i$1, j));
     }
@@ -4123,10 +4181,11 @@ function parse(multiline, dollar_endonly, dotall, ungreedy, s) {
   };
   var res = regexp$p(branch$p(/* [] */0));
   if (i.contents !== l) {
-    throw {
-          MEL_EXN_ID: Parse_error,
-          Error: new Error()
-        };
+    throw new Error(Parse_error, {
+              cause: {
+                MEL_EXN_ID: Parse_error
+              }
+            });
   }
   return res;
 }
@@ -4166,10 +4225,11 @@ function exec(rex, pos, s) {
   var len;
   var substr = exec_internal("Re.exec", pos, len, true, rex, s);
   if (typeof substr === "number") {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   return substr._0;
 }
diff --git a/jscomp/test/dist/jscomp/test/ocaml_typedtree_test.js b/jscomp/test/dist/jscomp/test/ocaml_typedtree_test.js
index 79b4eb099e..31b47e14a1 100644
--- a/jscomp/test/dist/jscomp/test/ocaml_typedtree_test.js
+++ b/jscomp/test/dist/jscomp/test/ocaml_typedtree_test.js
@@ -47,7 +47,9 @@ try {
 catch (raw_exn){
   var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
   if (exn.MEL_EXN_ID !== Stdlib.Not_found) {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   
 }
@@ -165,10 +167,11 @@ var Fatal_error = /* @__PURE__ */Caml_exceptions.create("Ocaml_typedtree_test.Mi
 function fatal_error(msg) {
   Stdlib.prerr_string(">> Fatal error: ");
   console.error(msg);
-  throw {
-        MEL_EXN_ID: Fatal_error,
-        Error: new Error()
-      };
+  throw new Error(Fatal_error, {
+            cause: {
+              MEL_EXN_ID: Fatal_error
+            }
+          });
 }
 
 function try_finally(work, cleanup) {
@@ -178,7 +181,9 @@ function try_finally(work, cleanup) {
   }
   catch (e){
     Curry._1(cleanup, undefined);
-    throw e;
+    throw new Error(e.MEL_EXN_ID, {
+              cause: e
+            });
   }
   Curry._1(cleanup, undefined);
   return result;
@@ -247,15 +252,16 @@ function split_last(param) {
             match[1]
           ];
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          817,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                817,
+                10
+              ]
+            }
+          });
 }
 
 function may(f, param) {
@@ -290,10 +296,11 @@ function find_in_path_uncap(path, name) {
       _param = param.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -306,7 +313,9 @@ function remove_file(filename) {
     if (exn.MEL_EXN_ID === Stdlib.Sys_error) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -327,7 +336,9 @@ function chop_extension_if_any(fname) {
     if (exn.MEL_EXN_ID === Stdlib.Invalid_argument) {
       return fname;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -489,21 +500,23 @@ function style_of_tag(param) {
       case "warning" :
           return cur_styles.contents.warning;
       default:
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     }
   } else {
-    throw {
-          MEL_EXN_ID: "Match_failure",
-          _1: [
-            "ocaml_typedtree_test.ml",
-            1191,
-            19
-          ],
-          Error: new Error()
-        };
+    throw new Error("Match_failure", {
+              cause: {
+                MEL_EXN_ID: "Match_failure",
+                _1: [
+                  "ocaml_typedtree_test.ml",
+                  1191,
+                  19
+                ]
+              }
+            });
   }
 }
 
@@ -529,7 +542,9 @@ function set_color_tag_handling(ppf) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         return Curry._1(partial_arg, param);
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   var functions$p_mark_close_stag = function (param) {
@@ -549,7 +564,9 @@ function set_color_tag_handling(ppf) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         return Curry._1(partial_arg$1, param);
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   var functions$p_print_open_stag = functions.print_open_stag;
@@ -902,15 +919,16 @@ function letter(param) {
                 tl: /* [] */0
               };
     default:
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              1587,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    1587,
+                    9
+                  ]
+                }
+              });
   }
 }
 
@@ -972,11 +990,12 @@ function parse_opt(error, active, flags, s) {
     var match$1 = get_num(0, i$1 + 2 | 0);
     var n2 = match$1[1];
     if (n2 < n1) {
-      throw {
-            MEL_EXN_ID: Stdlib__Arg.Bad,
-            _1: "Ill-formed list of warnings",
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Arg.Bad, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Arg.Bad,
+                  _1: "Ill-formed list of warnings"
+                }
+              });
     }
     return [
             match$1[0],
@@ -994,22 +1013,24 @@ function parse_opt(error, active, flags, s) {
       if (c >= 65) {
         if (c >= 97) {
           if (c >= 123) {
-            throw {
-                  MEL_EXN_ID: Stdlib__Arg.Bad,
-                  _1: "Ill-formed list of warnings",
-                  Error: new Error()
-                };
+            throw new Error(Stdlib__Arg.Bad, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib__Arg.Bad,
+                        _1: "Ill-formed list of warnings"
+                      }
+                    });
           }
           Stdlib__List.iter(clear, letter(Caml_string.get(s, i)));
           _i = i + 1 | 0;
           continue ;
         }
         if (c >= 91) {
-          throw {
-                MEL_EXN_ID: Stdlib__Arg.Bad,
-                _1: "Ill-formed list of warnings",
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Arg.Bad, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Arg.Bad,
+                      _1: "Ill-formed list of warnings"
+                    }
+                  });
         }
         Stdlib__List.iter(set, letter(Stdlib__Char.lowercase_ascii(Caml_string.get(s, i))));
         _i = i + 1 | 0;
@@ -1019,72 +1040,79 @@ function parse_opt(error, active, flags, s) {
         if (c >= 64) {
           return loop_letter_num(set_all, i + 1 | 0);
         }
-        throw {
-              MEL_EXN_ID: Stdlib__Arg.Bad,
-              _1: "Ill-formed list of warnings",
-              Error: new Error()
-            };
+        throw new Error(Stdlib__Arg.Bad, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib__Arg.Bad,
+                    _1: "Ill-formed list of warnings"
+                  }
+                });
       }
       if (c >= 43) {
         switch (c) {
           case 43 :
               return loop_letter_num(set, i + 1 | 0);
           case 44 :
-              throw {
-                    MEL_EXN_ID: Stdlib__Arg.Bad,
-                    _1: "Ill-formed list of warnings",
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib__Arg.Bad, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib__Arg.Bad,
+                          _1: "Ill-formed list of warnings"
+                        }
+                      });
           case 45 :
               return loop_letter_num(clear, i + 1 | 0);
           
         }
       } else {
-        throw {
-              MEL_EXN_ID: Stdlib__Arg.Bad,
-              _1: "Ill-formed list of warnings",
-              Error: new Error()
-            };
+        throw new Error(Stdlib__Arg.Bad, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib__Arg.Bad,
+                    _1: "Ill-formed list of warnings"
+                  }
+                });
       }
     };
   };
   var loop_letter_num = function (myset, i) {
     if (i >= s.length) {
-      throw {
-            MEL_EXN_ID: Stdlib__Arg.Bad,
-            _1: "Ill-formed list of warnings",
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Arg.Bad, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Arg.Bad,
+                  _1: "Ill-formed list of warnings"
+                }
+              });
     }
     var match = Caml_string.get(s, i);
     if (match >= 65) {
       if (match >= 97) {
         if (match >= 123) {
-          throw {
-                MEL_EXN_ID: Stdlib__Arg.Bad,
-                _1: "Ill-formed list of warnings",
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Arg.Bad, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Arg.Bad,
+                      _1: "Ill-formed list of warnings"
+                    }
+                  });
         }
         Stdlib__List.iter(myset, letter(Caml_string.get(s, i)));
         return loop(i + 1 | 0);
       }
       if (match >= 91) {
-        throw {
-              MEL_EXN_ID: Stdlib__Arg.Bad,
-              _1: "Ill-formed list of warnings",
-              Error: new Error()
-            };
+        throw new Error(Stdlib__Arg.Bad, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib__Arg.Bad,
+                    _1: "Ill-formed list of warnings"
+                  }
+                });
       }
       Stdlib__List.iter(myset, letter(Stdlib__Char.lowercase_ascii(Caml_string.get(s, i))));
       return loop(i + 1 | 0);
     }
     if (match > 57 || match < 48) {
-      throw {
-            MEL_EXN_ID: Stdlib__Arg.Bad,
-            _1: "Ill-formed list of warnings",
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Arg.Bad, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Arg.Bad,
+                  _1: "Ill-formed list of warnings"
+                }
+              });
     }
     var match$1 = get_range(i);
     for(var n = match$1[1] ,n_finish = Caml.caml_int_min(match$1[2], 104); n <= n_finish; ++n){
@@ -1178,15 +1206,16 @@ function message(param) {
               return "the method " + (lab + " is overridden.");
             }
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  1694,
-                  26
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        1694,
+                        26
+                      ]
+                    }
+                  });
       case /* Partial_match */3 :
           var s$1 = param._0;
           if (s$1 === "") {
@@ -1215,15 +1244,16 @@ function message(param) {
               return "the instance variable " + (lab$1 + " is overridden.\nThe behaviour changed in ocaml 3.10 (previous behaviour was hiding.)");
             }
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  1714,
-                  37
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        1714,
+                        37
+                      ]
+                    }
+                  });
       case /* Implicit_public_methods */6 :
           return "the following private methods were made public implicitly:\n " + (Stdlib__String.concat(" ", param._0) + ".");
       case /* Undeclared_virtual_method */7 :
@@ -1346,15 +1376,16 @@ function message(param) {
           if (param._2) {
             return "this record of type " + (ty + (" contains fields that are \nnot visible in the current scope: " + (Stdlib__String.concat(" ", slist) + ".\nThey will not be selected if the type becomes unknown.")));
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  1776,
-                  39
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        1776,
+                        39
+                      ]
+                    }
+                  });
           break;
       case /* Ambiguous_name */24 :
           var slist$1 = param._0;
@@ -1364,15 +1395,16 @@ function message(param) {
           if (param._2) {
             return "these field labels belong to several types: " + (Stdlib__String.concat(" ", param._1) + "\nThe first one was selected. Please disambiguate if this is wrong.");
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  1785,
-                  36
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        1785,
+                        36
+                      ]
+                    }
+                  });
           break;
       case /* Disambiguated_name */25 :
           return "this use of " + (param._0 + " required disambiguation.");
@@ -1618,10 +1650,11 @@ function highlight_terminfo(ppf, num_lines, lb, locs) {
   Stdlib__Format.pp_print_flush(ppf, undefined);
   var pos0 = -lb.lex_abs_pos | 0;
   if (pos0 < 0) {
-    throw {
-          MEL_EXN_ID: Stdlib.Exit,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Exit, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Exit
+              }
+            });
   }
   var lines = num_loc_lines.contents;
   for(var i = pos0 ,i_finish = lb.lex_buffer_len; i < i_finish; ++i){
@@ -1631,10 +1664,11 @@ function highlight_terminfo(ppf, num_lines, lb, locs) {
     
   }
   if (lines >= (num_lines - 2 | 0)) {
-    throw {
-          MEL_EXN_ID: Stdlib.Exit,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Exit, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Exit
+              }
+            });
   }
   Caml_io.caml_ml_flush(Stdlib.stdout);
   Caml_external_polyfill.resolve("caml_terminfo_backup")(lines);
@@ -1671,10 +1705,11 @@ function highlight_terminfo(ppf, num_lines, lb, locs) {
 function highlight_dumb(ppf, lb, loc) {
   var pos0 = -lb.lex_abs_pos | 0;
   if (pos0 < 0) {
-    throw {
-          MEL_EXN_ID: Stdlib.Exit,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Exit, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Exit
+              }
+            });
   }
   var end_pos = (lb.lex_buffer_len - pos0 | 0) - 1 | 0;
   var line_start = 0;
@@ -1809,7 +1844,9 @@ function highlight_locations(ppf, locs) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             norepeat = false;
           } else {
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }
         if (norepeat) {
@@ -1825,7 +1862,9 @@ function highlight_locations(ppf, locs) {
           if (exn$1.MEL_EXN_ID === Stdlib.Exit) {
             return false;
           }
-          throw exn$1;
+          throw new Error(exn$1.MEL_EXN_ID, {
+                    cause: exn$1
+                  });
         }
       } else {
         status.contents = Caml_external_polyfill.resolve("caml_terminfo_setup")(Stdlib.stdout);
@@ -1845,7 +1884,9 @@ function highlight_locations(ppf, locs) {
         if (exn$2.MEL_EXN_ID === Stdlib.Exit) {
           return false;
         }
-        throw exn$2;
+        throw new Error(exn$2.MEL_EXN_ID, {
+                  cause: exn$2
+                });
       }
     }
   };
@@ -2441,25 +2482,27 @@ function balance(l, d, r) {
       if (lr) {
         return mknode(mknode(ll, ld, lr._0), lr._1, mknode(lr._2, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              2781,
-              11
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    2781,
+                    11
+                  ]
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            2781,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  2781,
+                  11
+                ]
+              }
+            });
   }
   if (hr <= (hl + 1 | 0)) {
     return mknode(l, d, r);
@@ -2477,25 +2520,27 @@ function balance(l, d, r) {
     if (rl) {
       return mknode(mknode(l, d, rl._0), rl._1, mknode(rl._2, r._1, r._2));
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            2790,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  2790,
+                  11
+                ]
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          2790,
-          11
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                2790,
+                11
+              ]
+            }
+          });
 }
 
 function add(id, data, param) {
@@ -2554,20 +2599,22 @@ function find_same(id, _param) {
               _param$1 = param$1.previous;
               continue ;
             }
-            throw {
-                  MEL_EXN_ID: Stdlib.Not_found,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Not_found, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Not_found
+                      }
+                    });
           };
         }
       }
       _param = c < 0 ? param._0 : param._2;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -2583,10 +2630,11 @@ function find_name(name, _param) {
       _param = c < 0 ? param._0 : param._2;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -2747,15 +2795,16 @@ function head(_param) {
           _param = param._0;
           continue ;
       case /* Papply */2 :
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  2970,
-                  22
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        2970,
+                        22
+                      ]
+                    }
+                  });
       
     }
   };
@@ -2972,17 +3021,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create$1(create$1(ll, lv, ld, lr.l), lr.v, lr.d, create$1(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -3004,17 +3055,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create$1(create$1(l, x, d, rl.l), rl.v, rl.d, create$1(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function is_empty(param) {
@@ -3080,10 +3133,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -3120,10 +3174,11 @@ function find_first(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -3197,10 +3252,11 @@ function find_last(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -3285,10 +3341,11 @@ function min_binding(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -3323,10 +3380,11 @@ function max_binding(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -3356,11 +3414,12 @@ function remove_min_binding(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.remove_min_elt"
+            }
+          });
 }
 
 function merge(t1, t2) {
@@ -3671,15 +3730,16 @@ function merge$1(f, s1, s2) {
     var match$1 = split(v2, s1);
     return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/stdlib/map.ml",
-          408,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/stdlib/map.ml",
+                408,
+                10
+              ]
+            }
+          });
 }
 
 function union(f, s1, s2) {
@@ -4159,17 +4219,19 @@ function bal$1(l, v, r) {
       if (lr) {
         return create$2(create$2(ll, lv, lr.l), lr.v, create$2(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -4189,17 +4251,19 @@ function bal$1(l, v, r) {
     if (rl) {
       return create$2(create$2(l, v, rl.l), rl.v, create$2(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$2(x, t) {
@@ -4288,10 +4352,11 @@ function min_elt(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -4304,11 +4369,12 @@ function remove_min_elt(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.remove_min_elt"
+            }
+          });
 }
 
 function concat$1(t1, t2) {
@@ -4617,17 +4683,19 @@ function bal$2(l, v, r) {
       if (lr) {
         return create$3(create$3(ll, lv, lr.l), lr.v, create$3(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -4647,17 +4715,19 @@ function bal$2(l, v, r) {
     if (rl) {
       return create$3(create$3(l, v, rl.l), rl.v, create$3(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$3(x, t) {
@@ -4746,10 +4816,11 @@ function min_elt$1(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -4762,11 +4833,12 @@ function remove_min_elt$1(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.remove_min_elt"
+            }
+          });
 }
 
 function concat$2(t1, t2) {
@@ -5038,17 +5110,19 @@ function bal$3(l, x, d, r) {
       if (lr) {
         return create$4(create$4(ll, lv, ld, lr.l), lr.v, lr.d, create$4(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -5070,17 +5144,19 @@ function bal$3(l, x, d, r) {
     if (rl) {
       return create$4(create$4(l, x, d, rl.l), rl.v, rl.d, create$4(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add$4(x, data, m) {
@@ -5138,10 +5214,11 @@ function find$1(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -5166,15 +5243,16 @@ var TypeHash = Stdlib__Hashtbl.Make({
     });
 
 function print_raw(param) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          4836,
-          16
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                4836,
+                16
+              ]
+            }
+          });
 }
 
 var pivot_level = -1;
@@ -5394,15 +5472,16 @@ function row_fixed(row) {
     case /* Tunivar */9 :
         return true;
     default:
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              4946,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    4946,
+                    9
+                  ]
+                }
+              });
   }
 }
 
@@ -5462,15 +5541,16 @@ function proxy(ty) {
             case /* Tunivar */9 :
                 return ty$1;
             default:
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      4976,
-                      15
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            4976,
+                            15
+                          ]
+                        }
+                      });
           }
         };
     case /* Tvariant */8 :
@@ -5580,15 +5660,16 @@ function iter_row(f, _row) {
         case /* Tunivar */9 :
             break;
         default:
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  5023,
-                  9
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        5023,
+                        9
+                      ]
+                    }
+                  });
       }
     }
     return may((function (param) {
@@ -5857,15 +5938,16 @@ function copy_kind(_param) {
       if (!param) {
         return /* Fpresent */0;
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              5172,
-              16
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    5172,
+                    16
+                  ]
+                }
+              });
     }
     var k = param._0.contents;
     if (k === undefined) {
@@ -5968,25 +6050,27 @@ function copy_type_desc(_keep_namesOpt, f, _ty) {
           _keep_namesOpt = undefined;
           continue ;
       case /* Tsubst */7 :
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  5199,
-                  27
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        5199,
+                        27
+                      ]
+                    }
+                  });
       case /* Tvariant */8 :
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  5194,
-                  27
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        5194,
+                        27
+                      ]
+                    }
+                  });
       case /* Tunivar */9 :
           return ty;
       case /* Tpoly */10 :
@@ -6014,15 +6098,16 @@ function copy_type_desc(_keep_namesOpt, f, _ty) {
                           
                       }
                     }
-                    throw {
-                          MEL_EXN_ID: "Assert_failure",
-                          _1: [
-                            "jscomp/test/ocaml_typedtree_test.ml",
-                            5184,
-                            26
-                          ],
-                          Error: new Error()
-                        };
+                    throw new Error("Assert_failure", {
+                              cause: {
+                                MEL_EXN_ID: "Assert_failure",
+                                _1: [
+                                  "jscomp/test/ocaml_typedtree_test.ml",
+                                  5184,
+                                  26
+                                ]
+                              }
+                            });
                   };
                 }), ty._1);
           return {
@@ -6067,15 +6152,16 @@ var new_kinds = {
 function dup_kind(r) {
   var match = r.contents;
   if (match !== undefined) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            5217,
-            40
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  5217,
+                  40
+                ]
+              }
+            });
   }
   if (Stdlib__List.memq(r, new_kinds.contents)) {
     return ;
@@ -6226,15 +6312,16 @@ function memorize_abbrev(mem, priv, path, v, v$p) {
 
 function forget_abbrev_rec(mem, path) {
   if (typeof mem === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            5329,
-            6
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  5329,
+                  6
+                ]
+              }
+            });
   }
   if (mem.TAG === /* Mcons */0) {
     if (same(path, mem._1)) {
@@ -6252,10 +6339,11 @@ function forget_abbrev_rec(mem, path) {
   }
   var mem$p = mem._0;
   mem$p.contents = forget_abbrev_rec(mem$p.contents, path);
-  throw {
-        MEL_EXN_ID: Stdlib.Exit,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Exit, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Exit
+            }
+          });
 }
 
 function forget_abbrev(mem, path) {
@@ -6268,7 +6356,9 @@ function forget_abbrev(mem, path) {
     if (exn.MEL_EXN_ID === Stdlib.Exit) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -6319,10 +6409,11 @@ function extract_label_aux(_hd, l, _param) {
       };
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -6495,15 +6586,16 @@ function rev_log(_accu, _param) {
     var accu = _accu;
     if (typeof param === "number") {
       if (param) {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                5465,
-                15
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      5465,
+                      15
+                    ]
+                  }
+                });
       }
       return accu;
     }
@@ -6525,11 +6617,12 @@ function backtrack(param) {
   var change = changes.contents;
   if (typeof change === "number") {
     if (change) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "Btype.backtrack",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "Btype.backtrack"
+                }
+              });
     }
     last_snapshot.contents = old;
     return ;
@@ -6565,24 +6658,26 @@ function read_cmi(filename) {
       var pre_len = cmi_magic_number.length - 3 | 0;
       if (Stdlib__String.sub(buffer, 0, pre_len) === Stdlib__String.sub(cmi_magic_number, 0, pre_len)) {
         var msg = buffer < cmi_magic_number ? "an older" : "a newer";
-        throw {
-              MEL_EXN_ID: $$Error$1,
-              _1: {
-                TAG: /* Wrong_version_interface */1,
-                _0: filename,
-                _1: msg
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$1, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$1,
+                    _1: {
+                      TAG: /* Wrong_version_interface */1,
+                      _0: filename,
+                      _1: msg
+                    }
+                  }
+                });
       }
-      throw {
-            MEL_EXN_ID: $$Error$1,
-            _1: {
-              TAG: /* Not_an_interface */0,
-              _0: filename
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$1, {
+                cause: {
+                  MEL_EXN_ID: $$Error$1,
+                  _1: {
+                    TAG: /* Not_an_interface */0,
+                    _0: filename
+                  }
+                }
+              });
     }
     var cmi = input_cmi(ic);
     Caml_external_polyfill.resolve("caml_ml_close_channel")(ic);
@@ -6592,35 +6687,40 @@ function read_cmi(filename) {
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.End_of_file) {
       Caml_external_polyfill.resolve("caml_ml_close_channel")(ic);
-      throw {
-            MEL_EXN_ID: $$Error$1,
-            _1: {
-              TAG: /* Corrupted_interface */2,
-              _0: filename
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$1, {
+                cause: {
+                  MEL_EXN_ID: $$Error$1,
+                  _1: {
+                    TAG: /* Corrupted_interface */2,
+                    _0: filename
+                  }
+                }
+              });
     }
     if (exn.MEL_EXN_ID === Stdlib.Failure) {
       Caml_external_polyfill.resolve("caml_ml_close_channel")(ic);
-      throw {
-            MEL_EXN_ID: $$Error$1,
-            _1: {
-              TAG: /* Corrupted_interface */2,
-              _0: filename
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$1, {
+                cause: {
+                  MEL_EXN_ID: $$Error$1,
+                  _1: {
+                    TAG: /* Corrupted_interface */2,
+                    _0: filename
+                  }
+                }
+              });
     }
     if (exn.MEL_EXN_ID === $$Error$1) {
       Caml_external_polyfill.resolve("caml_ml_close_channel")(ic);
-      throw {
-            MEL_EXN_ID: $$Error$1,
-            _1: exn._1,
-            Error: new Error()
-          };
+      throw new Error($$Error$1, {
+                cause: {
+                  MEL_EXN_ID: $$Error$1,
+                  _1: exn._1
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -6771,7 +6871,9 @@ function extract(l, tbl) {
                             tl: assc
                           };
                   }
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
               }), /* [] */0, l$1);
 }
@@ -7789,7 +7891,9 @@ function get_pre_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -7802,7 +7906,9 @@ function mark_pre_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -7826,7 +7932,9 @@ function get_post_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -7839,7 +7947,9 @@ function mark_post_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -7853,7 +7963,9 @@ function get_info(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -7875,7 +7987,9 @@ function get_text(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -7897,7 +8011,9 @@ function get_pre_extra_text(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -7919,7 +8035,9 @@ function get_post_extra_text(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -10230,25 +10348,27 @@ function bal$4(l, x, d, r) {
       if (lr) {
         return create$5(create$5(ll, lv, ld, lr._0), lr._1, lr._2, create$5(lr._3, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              8866,
-              11
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    8866,
+                    11
+                  ]
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            8866,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  8866,
+                  11
+                ]
+              }
+            });
   }
   if (hr <= (hl + 1 | 0)) {
     return create$5(l, x, d, r);
@@ -10262,25 +10382,27 @@ function bal$4(l, x, d, r) {
     if (rl) {
       return create$5(create$5(l, x, d, rl._0), rl._1, rl._2, create$5(rl._3, r._1, r._2, r._3));
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            8873,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  8873,
+                  11
+                ]
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          8873,
-          11
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                8873,
+                11
+              ]
+            }
+          });
 }
 
 function add$5(x, data, param) {
@@ -10324,10 +10446,11 @@ function find$2(x, _param) {
       _param = c < 0 ? param._0 : param._3;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -10461,7 +10584,9 @@ function module_path(s, p) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             return p;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Pdot */1 :
         return {
@@ -10496,7 +10621,9 @@ function modtype_path(s, p) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             return p;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Pdot */1 :
         return {
@@ -10522,7 +10649,9 @@ function type_path(s, p) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             return p;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Pdot */1 :
         return {
@@ -10730,15 +10859,16 @@ function typexp(s, ty) {
                           exit$3 = 5;
                           break;
                       default:
-                        throw {
-                              MEL_EXN_ID: "Assert_failure",
-                              _1: [
-                                "jscomp/test/ocaml_typedtree_test.ml",
-                                9179,
-                                23
-                              ],
-                              Error: new Error()
-                            };
+                        throw new Error("Assert_failure", {
+                                  cause: {
+                                    MEL_EXN_ID: "Assert_failure",
+                                    _1: [
+                                      "jscomp/test/ocaml_typedtree_test.ml",
+                                      9179,
+                                      23
+                                    ]
+                                  }
+                                });
                     }
                   }
                   if (exit$3 === 5) {
@@ -11097,7 +11227,9 @@ function modtype(s, mty) {
                 if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                   return mty;
                 }
-                throw exn;
+                throw new Error(exn.MEL_EXN_ID, {
+                          cause: exn
+                        });
               }
           case /* Pdot */1 :
               return {
@@ -11218,15 +11350,16 @@ function modtype_declaration(s, decl) {
 
 var add_delayed_check_forward = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              9717,
-              46
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    9717,
+                    46
+                  ]
+                }
+              });
     })
 };
 
@@ -11261,7 +11394,9 @@ function force(f, x) {
     case /* Done */0 :
         return x$1._0;
     case /* Raise */1 :
-        throw x$1._0;
+        throw new Error(x$1._0.MEL_EXN_ID, {
+                  cause: x$1._0
+                });
     case /* Thunk */2 :
         try {
           var y = Curry._1(f, x$1._0);
@@ -11277,7 +11412,9 @@ function force(f, x) {
             TAG: /* Raise */1,
             _0: e
           };
-          throw e;
+          throw new Error(e.MEL_EXN_ID, {
+                    cause: e
+                  });
         }
     
   }
@@ -11309,7 +11446,9 @@ function already_defined(s, tbl) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -11439,71 +11578,76 @@ function is_implicit_coercion(env) {
 
 var components_of_module$p = {
   contents: (function (env, sub, path, mty) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              9965,
-              32
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    9965,
+                    32
+                  ]
+                }
+              });
     })
 };
 
 var components_of_module_maker$p = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              9968,
-              37
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    9968,
+                    37
+                  ]
+                }
+              });
     })
 };
 
 var components_of_functor_appl$p = {
   contents: (function (f, p1, p2) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              9971,
-              23
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    9971,
+                    23
+                  ]
+                }
+              });
     })
 };
 
 var check_modtype_inclusion = {
   contents: (function (env, mty1, path1, mty2) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              9975,
-              35
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    9975,
+                    35
+                  ]
+                }
+              });
     })
 };
 
 var strengthen = {
   contents: (function (env, mty, path) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              9979,
-              28
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    9979,
+                    28
+                  ]
+                }
+              });
     })
 };
 
@@ -11552,17 +11696,19 @@ function bal$5(l, v, r) {
       if (lr) {
         return create$6(create$6(ll, lv, lr.l), lr.v, create$6(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -11582,17 +11728,19 @@ function bal$5(l, v, r) {
     if (rl) {
       return create$6(create$6(l, v, rl.l), rl.v, create$6(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$7(x, t) {
@@ -11686,13 +11834,14 @@ function check_consistency(ps) {
               if (!Caml_obj.caml_notequal(crco, match[0])) {
                 return ;
               }
-              throw {
-                    MEL_EXN_ID: Inconsistency,
-                    _1: name,
-                    _2: source,
-                    _3: match[1],
-                    Error: new Error()
-                  };
+              throw new Error(Inconsistency, {
+                        cause: {
+                          MEL_EXN_ID: Inconsistency,
+                          _1: name,
+                          _2: source,
+                          _3: match[1]
+                        }
+                      });
             }
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
@@ -11702,7 +11851,9 @@ function check_consistency(ps) {
                             source
                           ]);
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }), ps.ps_crcs);
     ps.ps_crcs_checked = true;
@@ -11711,18 +11862,21 @@ function check_consistency(ps) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Inconsistency) {
-      throw {
-            MEL_EXN_ID: $$Error$2,
-            _1: {
-              TAG: /* Inconsistent_import */1,
-              _0: exn._1,
-              _1: exn._3,
-              _2: exn._2
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$2, {
+                cause: {
+                  MEL_EXN_ID: $$Error$2,
+                  _1: {
+                    TAG: /* Inconsistent_import */1,
+                    _0: exn._1,
+                    _1: exn._3,
+                    _2: exn._2
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -11760,31 +11914,33 @@ function read_pers_struct(modname, filename) {
     ps_flags: flags
   };
   if (ps.ps_name !== modname) {
-    throw {
-          MEL_EXN_ID: $$Error$2,
-          _1: {
-            TAG: /* Illegal_renaming */0,
-            _0: modname,
-            _1: ps.ps_name,
-            _2: filename
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$2, {
+              cause: {
+                MEL_EXN_ID: $$Error$2,
+                _1: {
+                  TAG: /* Illegal_renaming */0,
+                  _0: modname,
+                  _1: ps.ps_name,
+                  _2: filename
+                }
+              }
+            });
   }
   add_import(name);
   Stdlib__List.iter((function (param) {
           if (recursive_types.contents) {
             return ;
           }
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: {
-                  TAG: /* Need_recursive_types */2,
-                  _0: ps.ps_name,
-                  _1: current_unit.contents
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: {
+                        TAG: /* Need_recursive_types */2,
+                        _0: ps.ps_name,
+                        _1: current_unit.contents
+                      }
+                    }
+                  });
         }), ps.ps_flags);
   Stdlib__Hashtbl.add(persistent_structures, modname, ps);
   return ps;
@@ -11793,10 +11949,11 @@ function read_pers_struct(modname, filename) {
 function find_pers_struct(checkOpt, name) {
   var check = checkOpt !== undefined ? checkOpt : true;
   if (name === "*predef*") {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   var r;
   try {
@@ -11807,7 +11964,9 @@ function find_pers_struct(checkOpt, name) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       r = undefined;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   var ps;
@@ -11816,10 +11975,11 @@ function find_pers_struct(checkOpt, name) {
     if (sg !== undefined) {
       ps = sg;
     } else {
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
   } else {
     add_import(name);
@@ -11831,12 +11991,15 @@ function find_pers_struct(checkOpt, name) {
       var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
       if (exn$1.MEL_EXN_ID === Stdlib.Not_found) {
         Stdlib__Hashtbl.add(persistent_structures, name, undefined);
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
       }
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
     ps = read_pers_struct(name, filename);
   }
@@ -11859,32 +12022,37 @@ function find_module_descr(path, env) {
             if (id.stamp === 0 && id.name !== current_unit.contents) {
               return find_pers_struct(undefined, id.name).ps_comps;
             }
-            throw {
-                  MEL_EXN_ID: Stdlib.Not_found,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Not_found, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Not_found
+                      }
+                    });
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Pdot */1 :
         var c = force(components_of_module_maker$p.contents, find_module_descr(path._0, env));
         if (c.TAG === /* Structure_comps */0) {
           return find$2(path._1, c._0.comp_components)[0];
         }
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     case /* Papply */2 :
         var p1 = path._0;
         var f = force(components_of_module_maker$p.contents, find_module_descr(p1, env));
         if (f.TAG !== /* Structure_comps */0) {
           return Curry._3(components_of_functor_appl$p.contents, f._0, p1, path._1);
         }
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     
   }
 }
@@ -11898,15 +12066,17 @@ function find$3(proj1, proj2, path, env) {
         if (c.TAG === /* Structure_comps */0) {
           return find$2(path._1, Curry._1(proj2, c._0))[0];
         }
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     case /* Papply */2 :
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     
   }
 }
@@ -11964,12 +12134,15 @@ function find_module(alias, path, env) {
                       md_loc: none
                     };
             }
-            throw {
-                  MEL_EXN_ID: Stdlib.Not_found,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Not_found, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Not_found
+                      }
+                    });
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Pdot */1 :
         var c = force(components_of_module_maker$p.contents, find_module_descr(path._0, env));
@@ -11982,19 +12155,21 @@ function find_module(alias, path, env) {
                   md_loc: none
                 };
         }
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     case /* Papply */2 :
         var p2 = path._1;
         var desc1 = find_module_descr(path._0, env);
         var f = force(components_of_module_maker$p.contents, desc1);
         if (f.TAG === /* Structure_comps */0) {
-          throw {
-                MEL_EXN_ID: Stdlib.Not_found,
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Not_found, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Not_found
+                    }
+                  });
         }
         var f$1 = f._0;
         var p = f$1.fcomp_res;
@@ -12017,7 +12192,9 @@ function find_module(alias, path, env) {
               Stdlib__Hashtbl.add(f$1.fcomp_subst_cache, p2, mty);
               md_type$1 = mty;
             } else {
-              throw exn$1;
+              throw new Error(exn$1.MEL_EXN_ID, {
+                        cause: exn$1
+                      });
             }
           }
         }
@@ -12107,9 +12284,13 @@ function normalize_path(lax, env, path) {
       if (tmp) {
         return path$1;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
 }
@@ -12122,28 +12303,32 @@ function normalize_path$1(oloc, env, path) {
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       if (oloc !== undefined) {
-        throw {
-              MEL_EXN_ID: $$Error$2,
-              _1: {
-                TAG: /* Missing_module */3,
-                _0: oloc,
-                _1: path,
-                _2: normalize_path(true, env, path)
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$2, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$2,
+                    _1: {
+                      TAG: /* Missing_module */3,
+                      _0: oloc,
+                      _1: path,
+                      _2: normalize_path(true, env, path)
+                    }
+                  }
+                });
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              10272,
-              28
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    10272,
+                    28
+                  ]
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -12161,10 +12346,11 @@ function find_type_expansion(path, env) {
   }
   var path$p = normalize_path$1(undefined, env, path);
   if (same(path, path$p)) {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   return [
           decl.type_params,
@@ -12196,10 +12382,11 @@ function find_type_expansion_opt(path, env) {
   }
   var path$p = normalize_path$1(undefined, env, path);
   if (same(path, path$p)) {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   return [
           decl.type_params,
@@ -12222,10 +12409,11 @@ function find_modtype_expansion(path, env) {
   if (mty !== undefined) {
     return mty;
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function is_functor_arg(_path, env) {
@@ -12242,7 +12430,9 @@ function is_functor_arg(_path, env) {
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
               return false;
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
       case /* Pdot */1 :
           _path = path._0;
@@ -12267,10 +12457,11 @@ function lookup_module_descr(lid, env) {
           var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             if (s === current_unit.contents) {
-              throw {
-                    MEL_EXN_ID: Stdlib.Not_found,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Not_found, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Not_found
+                        }
+                      });
             }
             var ps = find_pers_struct(undefined, s);
             return [
@@ -12285,7 +12476,9 @@ function lookup_module_descr(lid, env) {
                     ps.ps_comps
                   ];
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Ldot */1 :
         var s$1 = lid._1;
@@ -12303,10 +12496,11 @@ function lookup_module_descr(lid, env) {
                   match$1[0]
                 ];
         }
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     case /* Lapply */2 :
         var match$2 = lookup_module_descr(lid._0, env);
         var p1 = match$2[0];
@@ -12314,10 +12508,11 @@ function lookup_module_descr(lid, env) {
         var match$3 = find_module(false, p2, env);
         var f = force(components_of_module_maker$p.contents, match$2[1]);
         if (f.TAG === /* Structure_comps */0) {
-          throw {
-                MEL_EXN_ID: Stdlib.Not_found,
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Not_found, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Not_found
+                    }
+                  });
         }
         var f$1 = f._0;
         may(Curry._3(check_modtype_inclusion.contents, env, match$3.md_type, p2), f$1.fcomp_arg);
@@ -12345,10 +12540,11 @@ function lookup_module(load, lid, env) {
             switch (id.TAG | 0) {
               case /* Pident */0 :
                   if (id._0.name === "#recmod#") {
-                    throw {
-                          MEL_EXN_ID: Recmodule,
-                          Error: new Error()
-                        };
+                    throw new Error(Recmodule, {
+                              cause: {
+                                MEL_EXN_ID: Recmodule
+                              }
+                            });
                   }
                   break;
               case /* Pdot */1 :
@@ -12363,10 +12559,11 @@ function lookup_module(load, lid, env) {
           var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             if (s === current_unit.contents) {
-              throw {
-                    MEL_EXN_ID: Stdlib.Not_found,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Not_found, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Not_found
+                        }
+                      });
             }
             if (transparent_modules.contents && !load) {
               try {
@@ -12380,7 +12577,9 @@ function lookup_module(load, lid, env) {
                         _0: s
                       });
                 } else {
-                  throw exn$1;
+                  throw new Error(exn$1.MEL_EXN_ID, {
+                            cause: exn$1
+                          });
                 }
               }
             } else {
@@ -12395,7 +12594,9 @@ function lookup_module(load, lid, env) {
                     }
                   };
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Ldot */1 :
         var s$1 = lid._1;
@@ -12410,10 +12611,11 @@ function lookup_module(load, lid, env) {
                   _2: match$1[1]
                 };
         }
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     case /* Lapply */2 :
         var match$2 = lookup_module_descr(lid._0, env);
         var p2 = lookup_module(true, lid._1, env);
@@ -12426,10 +12628,11 @@ function lookup_module(load, lid, env) {
         };
         var f = force(components_of_module_maker$p.contents, match$2[1]);
         if (f.TAG === /* Structure_comps */0) {
-          throw {
-                MEL_EXN_ID: Stdlib.Not_found,
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Not_found, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Not_found
+                    }
+                  });
         }
         may(Curry._3(check_modtype_inclusion.contents, env, match$3.md_type, p2), f._0.fcomp_arg);
         return p;
@@ -12457,15 +12660,17 @@ function lookup(proj1, proj2, lid, env) {
                   match$1[0]
                 ];
         }
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     case /* Lapply */2 :
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     
   }
 }
@@ -12504,7 +12709,9 @@ function lookup_all_simple(proj1, proj2, shadow, lid, env) {
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
               comps = /* [] */0;
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
           return Stdlib__List.map((function (param) {
@@ -12516,15 +12723,17 @@ function lookup_all_simple(proj1, proj2, shadow, lid, env) {
                               ];
                       }), comps);
         }
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     case /* Lapply */2 :
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     
   }
 }
@@ -12624,7 +12833,9 @@ function mark_value_used(env, name, vd) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -12643,7 +12854,9 @@ function mark_type_used(env, name, vd) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -12663,7 +12876,9 @@ function mark_constructor_used(usage, env, name, vd, constr) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -12684,7 +12899,9 @@ function mark_extension_used(usage, env, ext, name) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -12704,17 +12921,20 @@ function set_type_used_callback(name, td, callback) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              10534,
-              22
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    10534,
+                    22
+                  ]
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   Stdlib__Hashtbl.replace(type_declarations, key, (function (param) {
           Curry._1(callback, old);
@@ -12747,7 +12967,9 @@ function mark_type_path(env, path) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -12755,28 +12977,30 @@ function ty_path(t) {
   var match = repr(t);
   var match$1 = match.desc;
   if (typeof match$1 === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            10564,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  10564,
+                  9
+                ]
+              }
+            });
   }
   if (match$1.TAG === /* Tconstr */3) {
     return match$1._0;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          10564,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                10564,
+                9
+              ]
+            }
+          });
 }
 
 function lookup_constructor(lid, env) {
@@ -12788,10 +13012,11 @@ function lookup_constructor(lid, env) {
     Curry._1(match$1[1], undefined);
     return desc;
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function is_lident(param) {
@@ -12826,9 +13051,13 @@ function lookup_all_constructors$1(lid, env) {
       if (is_lident(lid)) {
         return /* [] */0;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -12856,7 +13085,9 @@ function mark_constructor(usage, env, name, desc) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             return ;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     
   }
@@ -12868,17 +13099,20 @@ function mark_constructor(usage, env, name, desc) {
   catch (raw_exn$1){
     var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
     if (exn$1.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              10601,
-              64
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    10601,
+                    64
+                  ]
+                }
+              });
     }
-    throw exn$1;
+    throw new Error(exn$1.MEL_EXN_ID, {
+              cause: exn$1
+            });
   }
   var ty_name$1 = last(ty_path$2);
   mark_constructor_used(usage, env, ty_name$1, ty_decl, name);
@@ -12905,9 +13139,13 @@ function lookup_all_labels$1(lid, env) {
       if (is_lident(lid)) {
         return /* [] */0;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -12998,7 +13236,9 @@ function iter_types(f) {
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
               safe = false;
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
         } else {
@@ -13123,7 +13363,9 @@ function find_all_comps(proj, s, param) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -13242,17 +13484,20 @@ function add_gadt_instances(env, lv, tl) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              10759,
-              59
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    10759,
+                    59
+                  ]
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   set_typeset(r, Stdlib__List.fold_right(add$3, tl, r.contents));
 }
@@ -13265,17 +13510,20 @@ function add_gadt_instance_chain(env, lv, t) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              10768,
-              59
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    10768,
+                    59
+                  ]
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   var add_instance = function (t) {
     var t$1 = repr(t);
@@ -13304,7 +13552,9 @@ function scrape_alias(env, path, mty) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             return mty;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Mty_signature */1 :
     case /* Mty_functor */2 :
@@ -13319,7 +13569,9 @@ function scrape_alias(env, path, mty) {
           if (exn$1.MEL_EXN_ID === Stdlib.Not_found) {
             return mty;
           }
-          throw exn$1;
+          throw new Error(exn$1.MEL_EXN_ID, {
+                    cause: exn$1
+                  });
         }
     
   }
@@ -13825,7 +14077,9 @@ function prefix_idents_and_subst$1(root, sub, sg) {
       Stdlib__Hashtbl.add(prefixed_sg, root, sgs$1);
       sgs = sgs$1;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   try {
@@ -13844,7 +14098,9 @@ function prefix_idents_and_subst$1(root, sub, sg) {
       };
       return r;
     }
-    throw exn$1;
+    throw new Error(exn$1.MEL_EXN_ID, {
+              cause: exn$1
+            });
   }
 }
 
@@ -13858,7 +14114,9 @@ function add_to_tbl(id, decl, tbl) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       decls = /* [] */0;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   return add$5(id, {
@@ -13883,30 +14141,32 @@ function components_of_module(env, sub, path, mty) {
 
 function check_value_name(name, loc) {
   if (bs_only.contents && name === "|.") {
-    throw {
-          MEL_EXN_ID: $$Error$2,
-          _1: {
-            TAG: /* Illegal_value_name */4,
-            _0: loc,
-            _1: name
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$2, {
+              cause: {
+                MEL_EXN_ID: $$Error$2,
+                _1: {
+                  TAG: /* Illegal_value_name */4,
+                  _0: loc,
+                  _1: name
+                }
+              }
+            });
   }
   if (!(name.length !== 0 && Caml_string.get(name, 0) === /* '#' */35)) {
     return ;
   }
   for(var i = 1 ,i_finish = name.length; i < i_finish; ++i){
     if (Caml_string.get(name, i) === /* '#' */35) {
-      throw {
-            MEL_EXN_ID: $$Error$2,
-            _1: {
-              TAG: /* Illegal_value_name */4,
-              _0: loc,
-              _1: name
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$2, {
+                cause: {
+                  MEL_EXN_ID: $$Error$2,
+                  _1: {
+                    TAG: /* Illegal_value_name */4,
+                    _0: loc,
+                    _1: name
+                  }
+                }
+              });
     }
     
   }
@@ -14477,7 +14737,9 @@ function components_of_functor_appl(f, p1, p2) {
       Stdlib__Hashtbl.add(f.fcomp_cache, p2, comps);
       return comps;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -14605,25 +14867,27 @@ function add_local_constraint(id, info, elv, env) {
               flags: env$1.flags
             };
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            11231,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  11231,
+                  9
+                ]
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          11231,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                11231,
+                9
+              ]
+            }
+          });
 }
 
 function enter(store_fun, name, data, env) {
@@ -14893,7 +15157,9 @@ function save_signature(sg, modname, filename) {
     Caml_io.caml_ml_flush(oc);
     Caml_external_polyfill.resolve("caml_ml_close_channel")(oc);
     remove_file(filename);
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -15862,15 +16128,16 @@ register_error_of_exn(function (param) {
     });
 
 function ill_formed_ast(loc, s) {
-  throw {
-        MEL_EXN_ID: $$Error$3,
-        _1: {
-          TAG: /* Ill_formed_ast */6,
-          _0: loc,
-          _1: s
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$3, {
+            cause: {
+              MEL_EXN_ID: $$Error$3,
+              _1: {
+                TAG: /* Ill_formed_ast */6,
+                _0: loc,
+                _1: s
+              }
+            }
+          });
 }
 
 function mktyp(d) {
@@ -16190,15 +16457,16 @@ function mkexp_constraint(e, param) {
                 _2: t2
               });
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          12327,
-          18
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                12327,
+                18
+              ]
+            }
+          });
 }
 
 function array_function(str, name) {
@@ -16216,41 +16484,44 @@ function array_function(str, name) {
 }
 
 function unclosed(opening_name, opening_num, closing_name, closing_num) {
-  throw {
-        MEL_EXN_ID: $$Error$3,
-        _1: {
-          TAG: /* Unclosed */0,
-          _0: rhs_loc(opening_num),
-          _1: opening_name,
-          _2: rhs_loc(closing_num),
-          _3: closing_name
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$3, {
+            cause: {
+              MEL_EXN_ID: $$Error$3,
+              _1: {
+                TAG: /* Unclosed */0,
+                _0: rhs_loc(opening_num),
+                _1: opening_name,
+                _2: rhs_loc(closing_num),
+                _3: closing_name
+              }
+            }
+          });
 }
 
 function expecting(pos, nonterm) {
-  throw {
-        MEL_EXN_ID: $$Error$3,
-        _1: {
-          TAG: /* Expecting */1,
-          _0: rhs_loc(pos),
-          _1: nonterm
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$3, {
+            cause: {
+              MEL_EXN_ID: $$Error$3,
+              _1: {
+                TAG: /* Expecting */1,
+                _0: rhs_loc(pos),
+                _1: nonterm
+              }
+            }
+          });
 }
 
 function not_expecting(pos, nonterm) {
-  throw {
-        MEL_EXN_ID: $$Error$3,
-        _1: {
-          TAG: /* Not_expecting */2,
-          _0: rhs_loc(pos),
-          _1: nonterm
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$3, {
+            cause: {
+              MEL_EXN_ID: $$Error$3,
+              _1: {
+                TAG: /* Not_expecting */2,
+                _0: rhs_loc(pos),
+                _1: nonterm
+              }
+            }
+          });
 }
 
 function bigarray_function(str, name) {
@@ -16312,15 +16583,16 @@ function check_variable(vl, loc, v) {
   if (!Stdlib__List.mem(v, vl)) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: $$Error$3,
-        _1: {
-          TAG: /* Variable_in_scope */4,
-          _0: loc,
-          _1: v
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$3, {
+            cause: {
+              MEL_EXN_ID: $$Error$3,
+              _1: {
+                TAG: /* Variable_in_scope */4,
+                _0: loc,
+                _1: v
+              }
+            }
+          });
 }
 
 function varify_constructors(var_names, t) {
@@ -16728,11 +17000,12 @@ var yytransl_block = [
 
 var yyact = [
   (function (param) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "parser",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "parser"
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -16753,10 +17026,11 @@ var yyact = [
       return Stdlib__Parsing.peek_val(__caml_parser_env, 1);
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib.End_of_file,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.End_of_file, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.End_of_file
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -17143,15 +17417,16 @@ var yyact = [
       }
       if (exit === 1) {
         if (Caml_obj.caml_notequal(lbs.lbs_attributes, /* [] */0)) {
-          throw {
-                MEL_EXN_ID: $$Error$3,
-                _1: {
-                  TAG: /* Not_expecting */2,
-                  _0: lbs.lbs_loc,
-                  _1: "attributes"
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$3, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$3,
+                      _1: {
+                        TAG: /* Not_expecting */2,
+                        _0: lbs.lbs_loc,
+                        _1: "attributes"
+                      }
+                    }
+                  });
         }
         var bindings$1 = Stdlib__List.map((function (lb) {
                 return mk$17(lb.lb_loc, lb.lb_attributes, CamlinternalLazy.force(lb.lb_docs), CamlinternalLazy.force(lb.lb_text), lb.lb_pattern, lb.lb_expression);
@@ -17757,39 +18032,42 @@ var yyact = [
       var _3 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       var bindings = Stdlib__List.map((function (lb) {
               if (Caml_obj.caml_notequal(lb.lb_attributes, /* [] */0)) {
-                throw {
-                      MEL_EXN_ID: $$Error$3,
-                      _1: {
-                        TAG: /* Not_expecting */2,
-                        _0: lb.lb_loc,
-                        _1: "item attribute"
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$3, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$3,
+                            _1: {
+                              TAG: /* Not_expecting */2,
+                              _0: lb.lb_loc,
+                              _1: "item attribute"
+                            }
+                          }
+                        });
               }
               return mk$17(lb.lb_loc, undefined, undefined, undefined, lb.lb_pattern, lb.lb_expression);
             }), _1.lbs_bindings);
       if (_1.lbs_extension !== undefined) {
-        throw {
-              MEL_EXN_ID: $$Error$3,
-              _1: {
-                TAG: /* Not_expecting */2,
-                _0: _1.lbs_loc,
-                _1: "extension"
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$3, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$3,
+                    _1: {
+                      TAG: /* Not_expecting */2,
+                      _0: _1.lbs_loc,
+                      _1: "extension"
+                    }
+                  }
+                });
       }
       if (Caml_obj.caml_notequal(_1.lbs_attributes, /* [] */0)) {
-        throw {
-              MEL_EXN_ID: $$Error$3,
-              _1: {
-                TAG: /* Not_expecting */2,
-                _0: _1.lbs_loc,
-                _1: "attributes"
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$3, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$3,
+                    _1: {
+                      TAG: /* Not_expecting */2,
+                      _0: _1.lbs_loc,
+                      _1: "attributes"
+                    }
+                  }
+                });
       }
       return mkclass({
                   TAG: /* Pcl_let */4,
@@ -17970,10 +18248,11 @@ var yyact = [
       var _4 = Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       var _6 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       if (_1 === /* Override */0) {
-        throw {
-              MEL_EXN_ID: Escape_error,
-              Error: new Error()
-            };
+        throw new Error(Escape_error, {
+                  cause: {
+                    MEL_EXN_ID: Escape_error
+                  }
+                });
       }
       return [
               {
@@ -18046,10 +18325,11 @@ var yyact = [
       var _4 = Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       var _6 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       if (_1 === /* Override */0) {
-        throw {
-              MEL_EXN_ID: Escape_error,
-              Error: new Error()
-            };
+        throw new Error(Escape_error, {
+                  cause: {
+                    MEL_EXN_ID: Escape_error
+                  }
+                });
       }
       return [
               {
@@ -18069,10 +18349,11 @@ var yyact = [
       var _4 = Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       var _6 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       if (_1 === /* Override */0) {
-        throw {
-              MEL_EXN_ID: Escape_error,
-              Error: new Error()
-            };
+        throw new Error(Escape_error, {
+                  cause: {
+                    MEL_EXN_ID: Escape_error
+                  }
+                });
       }
       return [
               {
@@ -18611,15 +18892,16 @@ var yyact = [
       var _3 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       var bindings = Stdlib__List.map((function (lb) {
               if (Caml_obj.caml_notequal(lb.lb_attributes, /* [] */0)) {
-                throw {
-                      MEL_EXN_ID: $$Error$3,
-                      _1: {
-                        TAG: /* Not_expecting */2,
-                        _0: lb.lb_loc,
-                        _1: "item attribute"
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$3, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$3,
+                            _1: {
+                              TAG: /* Not_expecting */2,
+                              _0: lb.lb_loc,
+                              _1: "item attribute"
+                            }
+                          }
+                        });
               }
               return mk$17(lb.lb_loc, undefined, undefined, undefined, lb.lb_pattern, lb.lb_expression);
             }), _1.lbs_bindings);
@@ -18731,10 +19013,11 @@ var yyact = [
   (function (__caml_parser_env) {
       Stdlib__Parsing.peek_val(__caml_parser_env, 3);
       Stdlib__Parsing.peek_val(__caml_parser_env, 2);
-      throw {
-            MEL_EXN_ID: Escape_error,
-            Error: new Error()
-          };
+      throw new Error(Escape_error, {
+                cause: {
+                  MEL_EXN_ID: Escape_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -20297,16 +20580,18 @@ var yyact = [
             ];
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Escape_error,
-            Error: new Error()
-          };
+      throw new Error(Escape_error, {
+                cause: {
+                  MEL_EXN_ID: Escape_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Escape_error,
-            Error: new Error()
-          };
+      throw new Error(Escape_error, {
+                cause: {
+                  MEL_EXN_ID: Escape_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -21442,17 +21727,19 @@ var yyact = [
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       if (_2) {
         if (_2.tl) {
-          throw {
-                MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Parsing.Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                    }
+                  });
         }
         return _2.hd;
       }
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.Parse_error, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -21461,17 +21748,19 @@ var yyact = [
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       if (_2) {
         if (_2.tl) {
-          throw {
-                MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Parsing.Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                    }
+                  });
         }
         return _2.hd;
       }
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.Parse_error, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -22253,14 +22542,15 @@ var yyact = [
                 _1: _3
               };
       }
-      throw {
-            MEL_EXN_ID: $$Error$3,
-            _1: {
-              TAG: /* Applicative_path */3,
-              _0: symbol_rloc(undefined)
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$3, {
+                cause: {
+                  MEL_EXN_ID: $$Error$3,
+                  _1: {
+                    TAG: /* Applicative_path */3,
+                    _0: symbol_rloc(undefined)
+                  }
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -22771,53 +23061,60 @@ var yyact = [
             };
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     })
 ];
 
@@ -22883,16 +23180,17 @@ function assert_same_type(lexbuf, x, y) {
   var lhs = type_of_directive(x);
   var rhs = type_of_directive(y);
   if (lhs !== rhs) {
-    throw {
-          MEL_EXN_ID: $$Error$4,
-          _1: {
-            TAG: /* Conditional_expr_expected_type */7,
-            _0: lhs,
-            _1: rhs
-          },
-          _2: curr(lexbuf),
-          Error: new Error()
-        };
+    throw new Error($$Error$4, {
+              cause: {
+                MEL_EXN_ID: $$Error$4,
+                _1: {
+                  TAG: /* Conditional_expr_expected_type */7,
+                  _0: lhs,
+                  _1: rhs
+                },
+                _2: curr(lexbuf)
+              }
+            });
   }
   return y;
 }
@@ -22919,7 +23217,9 @@ catch (raw_exn$1){
   if (exn$2.MEL_EXN_ID === Stdlib.Not_found) {
     tmp = "";
   } else {
-    throw exn$2;
+    throw new Error(exn$2.MEL_EXN_ID, {
+              cause: exn$2
+            });
   }
 }
 
@@ -23035,7 +23335,9 @@ function query(loc, str) {
                   _0: false
                 };
         }
-        throw exn$1;
+        throw new Error(exn$1.MEL_EXN_ID, {
+                  cause: exn$1
+                });
       }
       if (exit === 2) {
         try {
@@ -23069,7 +23371,9 @@ function query(loc, str) {
       }
       
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   if (typeof v === "number") {
@@ -23096,12 +23400,13 @@ function value_of_token(loc, t) {
                   _0: true
                 };
       default:
-        throw {
-              MEL_EXN_ID: $$Error$4,
-              _1: /* Unexpected_token_in_conditional */4,
-              _2: loc,
-              Error: new Error()
-            };
+        throw new Error($$Error$4, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$4,
+                    _1: /* Unexpected_token_in_conditional */4,
+                    _2: loc
+                  }
+                });
     }
   } else {
     switch (t.TAG | 0) {
@@ -23123,12 +23428,13 @@ function value_of_token(loc, t) {
       case /* UIDENT */17 :
           return query(loc, t._0);
       default:
-        throw {
-              MEL_EXN_ID: $$Error$4,
-              _1: /* Unexpected_token_in_conditional */4,
-              _2: loc,
-              Error: new Error()
-            };
+        throw new Error($$Error$4, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$4,
+                    _1: /* Unexpected_token_in_conditional */4,
+                    _2: loc
+                  }
+                });
     }
   }
 }
@@ -23149,12 +23455,13 @@ function directive_parse(token_with_comments, lexbuf) {
       if (typeof t === "number") {
         switch (t) {
           case /* EOF */25 :
-              throw {
-                    MEL_EXN_ID: $$Error$4,
-                    _1: /* Unterminated_if */2,
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$4, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$4,
+                          _1: /* Unterminated_if */2,
+                          _2: curr(lexbuf)
+                        }
+                      });
           case /* EOL */100 :
               _param = undefined;
               continue ;
@@ -23175,15 +23482,16 @@ function directive_parse(token_with_comments, lexbuf) {
   };
   var push = function (e) {
     if (look_ahead.contents !== undefined) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              24607,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    24607,
+                    4
+                  ]
+                }
+              });
     }
     look_ahead.contents = e;
   };
@@ -23224,15 +23532,16 @@ function directive_parse(token_with_comments, lexbuf) {
                   var str = rhs._0;
                   var last_index = str.length - 1 | 0;
                   if (last_index < 0) {
-                    throw {
-                          MEL_EXN_ID: $$Error$4,
-                          _1: {
-                            TAG: /* Illegal_semver */6,
-                            _0: str
-                          },
-                          _2: curr_loc,
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$4, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$4,
+                                _1: {
+                                  TAG: /* Illegal_semver */6,
+                                  _0: str
+                                },
+                                _2: curr_loc
+                              }
+                            });
                   }
                   var v = str.charCodeAt(0);
                   var match;
@@ -23251,15 +23560,16 @@ function directive_parse(token_with_comments, lexbuf) {
                       switch (v) {
                         case 60 :
                             if (last_index === 0) {
-                              throw {
-                                    MEL_EXN_ID: $$Error$4,
-                                    _1: {
-                                      TAG: /* Illegal_semver */6,
-                                      _0: str
-                                    },
-                                    _2: curr_loc,
-                                    Error: new Error()
-                                  };
+                              throw new Error($$Error$4, {
+                                        cause: {
+                                          MEL_EXN_ID: $$Error$4,
+                                          _1: {
+                                            TAG: /* Illegal_semver */6,
+                                            _0: str
+                                          },
+                                          _2: curr_loc
+                                        }
+                                      });
                             }
                             match = str[1] === "=" ? [
                                 "Le",
@@ -23274,15 +23584,16 @@ function directive_parse(token_with_comments, lexbuf) {
                             break;
                         case 62 :
                             if (last_index === 0) {
-                              throw {
-                                    MEL_EXN_ID: $$Error$4,
-                                    _1: {
-                                      TAG: /* Illegal_semver */6,
-                                      _0: str
-                                    },
-                                    _2: curr_loc,
-                                    Error: new Error()
-                                  };
+                              throw new Error($$Error$4, {
+                                        cause: {
+                                          MEL_EXN_ID: $$Error$4,
+                                          _1: {
+                                            TAG: /* Illegal_semver */6,
+                                            _0: str
+                                          },
+                                          _2: curr_loc
+                                        }
+                                      });
                             }
                             match = str[1] === "=" ? [
                                 "Ge",
@@ -23341,30 +23652,32 @@ function directive_parse(token_with_comments, lexbuf) {
                 exit$2 = 3;
               }
               if (exit$2 === 3) {
-                throw {
-                      MEL_EXN_ID: $$Error$4,
-                      _1: {
-                        TAG: /* Conditional_expr_expected_type */7,
-                        _0: /* Dir_type_string */3,
-                        _1: type_of_directive(lhs)
-                      },
-                      _2: curr(lexbuf),
-                      Error: new Error()
-                    };
+                throw new Error($$Error$4, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$4,
+                            _1: {
+                              TAG: /* Conditional_expr_expected_type */7,
+                              _0: /* Dir_type_string */3,
+                              _1: type_of_directive(lhs)
+                            },
+                            _2: curr(lexbuf)
+                          }
+                        });
               }
               
             }
             if (exit$1 === 2) {
-              throw {
-                    MEL_EXN_ID: $$Error$4,
-                    _1: {
-                      TAG: /* Conditional_expr_expected_type */7,
-                      _0: /* Dir_type_string */3,
-                      _1: type_of_directive(lhs)
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$4, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$4,
+                          _1: {
+                            TAG: /* Conditional_expr_expected_type */7,
+                            _0: /* Dir_type_string */3,
+                            _1: type_of_directive(lhs)
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
             break;
         case "<=" :
@@ -23408,15 +23721,16 @@ function directive_parse(token_with_comments, lexbuf) {
         exit$4 = 2;
       }
       if (exit$4 === 2) {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                24626,
-                17
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      24626,
+                      17
+                    ]
+                  }
+                });
       }
       var curr_loc$1 = curr(lexbuf);
       var rhs$1 = value_of_token(curr_loc$1, token(undefined));
@@ -23473,52 +23787,56 @@ function directive_parse(token_with_comments, lexbuf) {
             if (match === 81) {
               return v;
             }
-            throw {
-                  MEL_EXN_ID: $$Error$4,
-                  _1: /* Unterminated_paren_in_conditional */1,
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$4, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$4,
+                        _1: /* Unterminated_paren_in_conditional */1,
+                        _2: curr(lexbuf)
+                      }
+                    });
         case /* TRUE */91 :
             return true;
         default:
-          throw {
-                MEL_EXN_ID: $$Error$4,
-                _1: /* Unexpected_token_in_conditional */4,
-                _2: curr_loc,
-                Error: new Error()
-              };
+          throw new Error($$Error$4, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$4,
+                      _1: /* Unexpected_token_in_conditional */4,
+                      _2: curr_loc
+                    }
+                  });
       }
     } else {
       switch (curr_token.TAG | 0) {
         case /* FLOAT */1 :
             return token_op(calc, (function (e) {
-                          throw {
-                                MEL_EXN_ID: $$Error$4,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: /* Dir_type_float */1
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$4, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$4,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: /* Dir_type_float */1
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), {
                         TAG: /* Dir_float */1,
                         _0: Caml_format.caml_float_of_string(curr_token._0)
                       });
         case /* INT */7 :
             return token_op(calc, (function (e) {
-                          throw {
-                                MEL_EXN_ID: $$Error$4,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: /* Dir_type_int */2
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$4, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$4,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: /* Dir_type_int */2
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), {
                         TAG: /* Dir_int */2,
                         _0: curr_token._0
@@ -23530,22 +23848,24 @@ function directive_parse(token_with_comments, lexbuf) {
               case "undefined" :
                   break;
               default:
-                throw {
-                      MEL_EXN_ID: $$Error$4,
-                      _1: /* Unexpected_token_in_conditional */4,
-                      _2: curr_loc,
-                      Error: new Error()
-                    };
+                throw new Error($$Error$4, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$4,
+                            _1: /* Unexpected_token_in_conditional */4,
+                            _2: curr_loc
+                          }
+                        });
             }
             var t = token(undefined);
             var loc = curr(lexbuf);
             if (typeof t === "number") {
-              throw {
-                    MEL_EXN_ID: $$Error$4,
-                    _1: /* Unexpected_token_in_conditional */4,
-                    _2: loc,
-                    Error: new Error()
-                  };
+              throw new Error($$Error$4, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$4,
+                          _1: /* Unexpected_token_in_conditional */4,
+                          _2: loc
+                        }
+                      });
             }
             if (t.TAG === /* UIDENT */17) {
               var s = t._0;
@@ -23559,25 +23879,27 @@ function directive_parse(token_with_comments, lexbuf) {
                 return true;
               }
             }
-            throw {
-                  MEL_EXN_ID: $$Error$4,
-                  _1: /* Unexpected_token_in_conditional */4,
-                  _2: loc,
-                  Error: new Error()
-                };
+            throw new Error($$Error$4, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$4,
+                        _1: /* Unexpected_token_in_conditional */4,
+                        _2: loc
+                      }
+                    });
             break;
         case /* STRING */16 :
             return token_op(calc, (function (e) {
-                          throw {
-                                MEL_EXN_ID: $$Error$4,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: /* Dir_type_string */3
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$4, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$4,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: /* Dir_type_string */3
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), {
                         TAG: /* Dir_string */3,
                         _0: curr_token._0[0]
@@ -23590,24 +23912,26 @@ function directive_parse(token_with_comments, lexbuf) {
                             return value_v._0;
                           }
                           var ty = type_of_directive(value_v);
-                          throw {
-                                MEL_EXN_ID: $$Error$4,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: ty
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$4, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$4,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: ty
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), value_v);
         default:
-          throw {
-                MEL_EXN_ID: $$Error$4,
-                _1: /* Unexpected_token_in_conditional */4,
-                _2: curr_loc,
-                Error: new Error()
-              };
+          throw new Error($$Error$4, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$4,
+                      _1: /* Unexpected_token_in_conditional */4,
+                      _2: curr_loc
+                    }
+                  });
       }
     }
   };
@@ -23616,12 +23940,13 @@ function directive_parse(token_with_comments, lexbuf) {
   if (match === 88) {
     return v;
   }
-  throw {
-        MEL_EXN_ID: $$Error$4,
-        _1: /* Expect_hash_then_in_conditional */5,
-        _2: curr(lexbuf),
-        Error: new Error()
-      };
+  throw new Error($$Error$4, {
+            cause: {
+              MEL_EXN_ID: $$Error$4,
+              _1: /* Expect_hash_then_in_conditional */5,
+              _2: curr(lexbuf)
+            }
+          });
 }
 
 function is_elif(i) {
@@ -24111,15 +24436,16 @@ function char_for_decimal_code(lexbuf, i) {
   if (Caml_obj.caml_notequal(comment_start_loc.contents, /* [] */0)) {
     return /* 'x' */120;
   }
-  throw {
-        MEL_EXN_ID: $$Error$4,
-        _1: {
-          TAG: /* Illegal_escape */1,
-          _0: Stdlib__Lexing.lexeme(lexbuf)
-        },
-        _2: curr(lexbuf),
-        Error: new Error()
-      };
+  throw new Error($$Error$4, {
+            cause: {
+              MEL_EXN_ID: $$Error$4,
+              _1: {
+                TAG: /* Illegal_escape */1,
+                _0: Stdlib__Lexing.lexeme(lexbuf)
+              },
+              _2: curr(lexbuf)
+            }
+          });
 }
 
 function char_for_hexadecimal_code(lexbuf, i) {
@@ -24147,15 +24473,16 @@ function cvt_int64_literal(s) {
 }
 
 function cvt_nativeint_literal(s) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          24914,
-          30
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                24914,
+                30
+              ]
+            }
+          });
 }
 
 function remove_underscores(s) {
@@ -24189,15 +24516,16 @@ function get_label_name(lexbuf) {
   var s = Stdlib__Lexing.lexeme(lexbuf);
   var name = Stdlib__String.sub(s, 1, s.length - 2 | 0);
   if (Stdlib__Hashtbl.mem(keyword_table, name)) {
-    throw {
-          MEL_EXN_ID: $$Error$4,
-          _1: {
-            TAG: /* Keyword_as_label */4,
-            _0: name
-          },
-          _2: curr(lexbuf),
-          Error: new Error()
-        };
+    throw new Error($$Error$4, {
+              cause: {
+                MEL_EXN_ID: $$Error$4,
+                _1: {
+                  TAG: /* Keyword_as_label */4,
+                  _0: name
+                },
+                _2: curr(lexbuf)
+              }
+            });
   }
   return name;
 }
@@ -24475,15 +24803,16 @@ function token(lexbuf) {
     switch (__ocaml_lex_state$1) {
       case 0 :
           if (!escaped_newlines.contents) {
-            throw {
-                  MEL_EXN_ID: $$Error$4,
-                  _1: {
-                    TAG: /* Illegal_character */0,
-                    _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
-                  },
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$4, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$4,
+                        _1: {
+                          TAG: /* Illegal_character */0,
+                          _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
+                        },
+                        _2: curr(lexbuf)
+                      }
+                    });
           }
           update_loc(lexbuf, undefined, 1, false, 0);
           return token(lexbuf);
@@ -24539,7 +24868,9 @@ function token(lexbuf) {
                       _0: s
                     };
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
       case 11 :
           prerr_warning(curr(lexbuf), {
@@ -24574,17 +24905,20 @@ function token(lexbuf) {
           catch (raw_exn$1){
             var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
             if (exn$1.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$4,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "int"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$4, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$4,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "int"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
       case 15 :
           return {
@@ -24601,17 +24935,20 @@ function token(lexbuf) {
           catch (raw_exn$2){
             var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
             if (exn$2.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$4,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "int32"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$4, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$4,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "int32"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$2;
+            throw new Error(exn$2.MEL_EXN_ID, {
+                      cause: exn$2
+                    });
           }
       case 17 :
           try {
@@ -24623,17 +24960,20 @@ function token(lexbuf) {
           catch (raw_exn$3){
             var exn$3 = Caml_js_exceptions.internalToOCamlException(raw_exn$3);
             if (exn$3.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$4,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "int64"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$4, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$4,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "int64"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$3;
+            throw new Error(exn$3.MEL_EXN_ID, {
+                      cause: exn$3
+                    });
           }
       case 18 :
           try {
@@ -24645,17 +24985,20 @@ function token(lexbuf) {
           catch (raw_exn$4){
             var exn$4 = Caml_js_exceptions.internalToOCamlException(raw_exn$4);
             if (exn$4.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$4,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "nativeint"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$4, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$4,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "nativeint"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$4;
+            throw new Error(exn$4.MEL_EXN_ID, {
+                      cause: exn$4
+                    });
           }
       case 19 :
           reset_string_buffer(undefined);
@@ -24718,15 +25061,16 @@ function token(lexbuf) {
       case 26 :
           var l = Stdlib__Lexing.lexeme(lexbuf);
           var esc = Stdlib__String.sub(l, 1, l.length - 1 | 0);
-          throw {
-                MEL_EXN_ID: $$Error$4,
-                _1: {
-                  TAG: /* Illegal_escape */1,
-                  _0: esc
-                },
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$4, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$4,
+                      _1: {
+                        TAG: /* Illegal_escape */1,
+                        _0: esc
+                      },
+                      _2: curr(lexbuf)
+                    }
+                  });
       case 27 :
           var match = with_comment_buffer(comment, lexbuf);
           return {
@@ -24935,29 +25279,32 @@ function token(lexbuf) {
             return /* EOF */25;
           }
           if (if_then_else.contents === /* Dir_if_true */0) {
-            throw {
-                  MEL_EXN_ID: $$Error$4,
-                  _1: /* Unterminated_if */2,
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$4, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$4,
+                        _1: /* Unterminated_if */2,
+                        _2: curr(lexbuf)
+                      }
+                    });
           }
-          throw {
-                MEL_EXN_ID: $$Error$4,
-                _1: /* Unterminated_else */3,
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$4, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$4,
+                      _1: /* Unterminated_else */3,
+                      _2: curr(lexbuf)
+                    }
+                  });
       case 91 :
-          throw {
-                MEL_EXN_ID: $$Error$4,
-                _1: {
-                  TAG: /* Illegal_character */0,
-                  _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
-                },
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$4, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$4,
+                      _1: {
+                        TAG: /* Illegal_character */0,
+                        _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
+                      },
+                      _2: curr(lexbuf)
+                    }
+                  });
       default:
         Curry._1(lexbuf.refill_buff, lexbuf);
         ___ocaml_lex_state = __ocaml_lex_state$1;
@@ -24978,12 +25325,13 @@ function __ocaml_lex_quoted_string_rec(delim, lexbuf, ___ocaml_lex_state) {
           continue ;
       case 1 :
           is_in_string.contents = false;
-          throw {
-                MEL_EXN_ID: $$Error$4,
-                _1: /* Unterminated_string */0,
-                _2: string_start_loc.contents,
-                Error: new Error()
-              };
+          throw new Error($$Error$4, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$4,
+                      _1: /* Unterminated_string */0,
+                      _2: string_start_loc.contents
+                    }
+                  });
       case 2 :
           var edelim = Stdlib__Lexing.lexeme(lexbuf);
           var edelim$1 = Stdlib__String.sub(edelim, 1, edelim.length - 2 | 0);
@@ -25045,12 +25393,13 @@ function string(lexbuf) {
           return string(lexbuf);
       case 7 :
           is_in_string.contents = false;
-          throw {
-                MEL_EXN_ID: $$Error$4,
-                _1: /* Unterminated_string */0,
-                _2: string_start_loc.contents,
-                Error: new Error()
-              };
+          throw new Error($$Error$4, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$4,
+                      _1: /* Unterminated_string */0,
+                      _2: string_start_loc.contents
+                    }
+                  });
       case 8 :
           store_string_char(Stdlib__Lexing.lexeme_char(lexbuf, 0));
           return string(lexbuf);
@@ -25091,15 +25440,16 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
             comment_start_loc.contents = /* [] */0;
             return curr(lexbuf);
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  26844,
-                  16
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        26844,
+                        16
+                      ]
+                    }
+                  });
       case 2 :
           string_start_loc.contents = curr(lexbuf);
           store_string_char(/* '"' */34);
@@ -25113,36 +25463,44 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
               var match$1 = exn._1;
               if (typeof match$1 === "number") {
                 if (match$1) {
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
                 var match$2 = comment_start_loc.contents;
                 if (match$2) {
                   var start = Stdlib__List.hd(Stdlib__List.rev(comment_start_loc.contents));
                   comment_start_loc.contents = /* [] */0;
-                  throw {
-                        MEL_EXN_ID: $$Error$4,
-                        _1: {
-                          TAG: /* Unterminated_string_in_comment */3,
-                          _0: start,
-                          _1: exn._2
-                        },
-                        _2: match$2.hd,
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$4, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$4,
+                              _1: {
+                                TAG: /* Unterminated_string_in_comment */3,
+                                _0: start,
+                                _1: exn._2
+                              },
+                              _2: match$2.hd
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        26861,
-                        18
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              26861,
+                              18
+                            ]
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           is_in_string.contents = false;
           store_string_char(/* '"' */34);
@@ -25163,36 +25521,44 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
               var match$3 = exn$1._1;
               if (typeof match$3 === "number") {
                 if (match$3) {
-                  throw exn$1;
+                  throw new Error(exn$1.MEL_EXN_ID, {
+                            cause: exn$1
+                          });
                 }
                 var match$4 = comment_start_loc.contents;
                 if (match$4) {
                   var start$1 = Stdlib__List.hd(Stdlib__List.rev(comment_start_loc.contents));
                   comment_start_loc.contents = /* [] */0;
-                  throw {
-                        MEL_EXN_ID: $$Error$4,
-                        _1: {
-                          TAG: /* Unterminated_string_in_comment */3,
-                          _0: start$1,
-                          _1: exn$1._2
-                        },
-                        _2: match$4.hd,
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$4, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$4,
+                              _1: {
+                                TAG: /* Unterminated_string_in_comment */3,
+                                _0: start$1,
+                                _1: exn$1._2
+                              },
+                              _2: match$4.hd
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        26884,
-                        18
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              26884,
+                              18
+                            ]
+                          }
+                        });
               }
-              throw exn$1;
+              throw new Error(exn$1.MEL_EXN_ID, {
+                        cause: exn$1
+                      });
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
           is_in_string.contents = false;
           store_string_char(/* '|' */124);
@@ -25210,25 +25576,27 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
           if (match$5) {
             var start$2 = Stdlib__List.hd(Stdlib__List.rev(comment_start_loc.contents));
             comment_start_loc.contents = /* [] */0;
-            throw {
-                  MEL_EXN_ID: $$Error$4,
-                  _1: {
-                    TAG: /* Unterminated_comment */2,
-                    _0: start$2
-                  },
-                  _2: match$5.hd,
-                  Error: new Error()
-                };
+            throw new Error($$Error$4, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$4,
+                        _1: {
+                          TAG: /* Unterminated_comment */2,
+                          _0: start$2
+                        },
+                        _2: match$5.hd
+                      }
+                    });
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  26934,
-                  16
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        26934,
+                        16
+                      ]
+                    }
+                  });
       case 11 :
           update_loc(lexbuf, undefined, 1, false, 0);
           store_string(Stdlib__Lexing.lexeme(lexbuf));
@@ -25321,22 +25689,24 @@ function token$1(lexbuf) {
                   switch (match) {
                     case /* ELSE */23 :
                         if (if_then_else$1) {
-                          throw {
-                                MEL_EXN_ID: $$Error$4,
-                                _1: /* Unexpected_directive */6,
-                                _2: curr(lexbuf),
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$4, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$4,
+                                      _1: /* Unexpected_directive */6,
+                                      _2: curr(lexbuf)
+                                    }
+                                  });
                         }
                         break;
                     case /* END */24 :
                         if (if_then_else$1 >= 2) {
-                          throw {
-                                MEL_EXN_ID: $$Error$4,
-                                _1: /* Unexpected_directive */6,
-                                _2: curr(lexbuf),
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$4, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$4,
+                                      _1: /* Unexpected_directive */6,
+                                      _2: curr(lexbuf)
+                                    }
+                                  });
                         }
                         if_then_else.contents = /* Dir_out */2;
                         return Curry._1(cont, lexbuf);
@@ -25350,12 +25720,13 @@ function token$1(lexbuf) {
                             while(true) {
                               var token = token_with_comments(lexbuf);
                               if (Caml_obj.caml_equal(token, /* EOF */25)) {
-                                throw {
-                                      MEL_EXN_ID: $$Error$4,
-                                      _1: /* Unterminated_if */2,
-                                      _2: curr(lexbuf),
-                                      Error: new Error()
-                                    };
+                                throw new Error($$Error$4, {
+                                          cause: {
+                                            MEL_EXN_ID: $$Error$4,
+                                            _1: /* Unterminated_if */2,
+                                            _2: curr(lexbuf)
+                                          }
+                                        });
                               }
                               if (Caml_obj.caml_equal(token, /* SHARP */84) && at_bol(lexbuf)) {
                                 var token$1 = token_with_comments(lexbuf);
@@ -25370,12 +25741,13 @@ function token$1(lexbuf) {
                                     }
                                   }
                                   if (token$1 === 37) {
-                                    throw {
-                                          MEL_EXN_ID: $$Error$4,
-                                          _1: /* Unexpected_directive */6,
-                                          _2: curr(lexbuf),
-                                          Error: new Error()
-                                        };
+                                    throw new Error($$Error$4, {
+                                              cause: {
+                                                MEL_EXN_ID: $$Error$4,
+                                                _1: /* Unexpected_directive */6,
+                                                _2: curr(lexbuf)
+                                              }
+                                            });
                                   }
                                   
                                 }
@@ -25391,12 +25763,13 @@ function token$1(lexbuf) {
                             };
                           }
                         }
-                        throw {
-                              MEL_EXN_ID: $$Error$4,
-                              _1: /* Unexpected_directive */6,
-                              _2: curr(lexbuf),
-                              Error: new Error()
-                            };
+                        throw new Error($$Error$4, {
+                                  cause: {
+                                    MEL_EXN_ID: $$Error$4,
+                                    _1: /* Unexpected_directive */6,
+                                    _2: curr(lexbuf)
+                                  }
+                                });
                     default:
                       return Curry._1(look_ahead, match);
                   }
@@ -25408,12 +25781,13 @@ function token$1(lexbuf) {
                     return Curry._1(look_ahead, match);
                   }
                   if (if_then_else$1) {
-                    throw {
-                          MEL_EXN_ID: $$Error$4,
-                          _1: /* Unexpected_directive */6,
-                          _2: curr(lexbuf),
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$4, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$4,
+                                _1: /* Unexpected_directive */6,
+                                _2: curr(lexbuf)
+                              }
+                            });
                   }
                   
                 }
@@ -25425,12 +25799,13 @@ function token$1(lexbuf) {
                   var else_seen = _else_seen;
                   var token$2 = token_with_comments(lexbuf);
                   if (Caml_obj.caml_equal(token$2, /* EOF */25)) {
-                    throw {
-                          MEL_EXN_ID: $$Error$4,
-                          _1: /* Unterminated_else */3,
-                          _2: curr(lexbuf),
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$4, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$4,
+                                _1: /* Unterminated_else */3,
+                                _2: curr(lexbuf)
+                              }
+                            });
                   }
                   if (Caml_obj.caml_equal(token$2, /* SHARP */84) && at_bol(lexbuf)) {
                     var token$3 = token_with_comments(lexbuf);
@@ -25441,33 +25816,36 @@ function token$1(lexbuf) {
                           return Curry._1(cont, lexbuf);
                         }
                         if (else_seen) {
-                          throw {
-                                MEL_EXN_ID: $$Error$4,
-                                _1: /* Unexpected_directive */6,
-                                _2: curr(lexbuf),
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$4, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$4,
+                                      _1: /* Unexpected_directive */6,
+                                      _2: curr(lexbuf)
+                                    }
+                                  });
                         }
                         _else_seen = true;
                         continue ;
                       }
                       if (token$3 === 37) {
-                        throw {
-                              MEL_EXN_ID: $$Error$4,
-                              _1: /* Unexpected_directive */6,
-                              _2: curr(lexbuf),
-                              Error: new Error()
-                            };
+                        throw new Error($$Error$4, {
+                                  cause: {
+                                    MEL_EXN_ID: $$Error$4,
+                                    _1: /* Unexpected_directive */6,
+                                    _2: curr(lexbuf)
+                                  }
+                                });
                       }
                       
                     }
                     if (else_seen && is_elif(token$3)) {
-                      throw {
-                            MEL_EXN_ID: $$Error$4,
-                            _1: /* Unexpected_directive */6,
-                            _2: curr(lexbuf),
-                            Error: new Error()
-                          };
+                      throw new Error($$Error$4, {
+                                cause: {
+                                  MEL_EXN_ID: $$Error$4,
+                                  _1: /* Unexpected_directive */6,
+                                  _2: curr(lexbuf)
+                                }
+                              });
                     }
                     continue ;
                   }
@@ -25603,7 +25981,9 @@ function skip_phrase(lexbuf) {
           if (tmp === /* Unterminated_string */0) {
             continue ;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         } else {
           switch (tmp.TAG | 0) {
             case /* Illegal_character */0 :
@@ -25611,11 +25991,15 @@ function skip_phrase(lexbuf) {
             case /* Unterminated_string_in_comment */3 :
                 continue ;
             default:
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
           }
         }
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
   };
@@ -25643,26 +26027,40 @@ function wrap$1(parsing_fun, lexbuf) {
     if (err.MEL_EXN_ID === $$Error$4) {
       var tmp = err._1;
       if (typeof tmp === "number") {
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       if (tmp.TAG === /* Illegal_character */0) {
         if (input_name.contents === "//toplevel//") {
           skip_phrase(lexbuf);
-          throw err;
+          throw new Error(err.MEL_EXN_ID, {
+                    cause: err
+                  });
         }
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
-      throw err;
+      throw new Error(err.MEL_EXN_ID, {
+                cause: err
+              });
     } else {
       if (err.MEL_EXN_ID === $$Error$3) {
         if (input_name.contents === "//toplevel//") {
           maybe_skip_phrase(lexbuf);
-          throw err;
+          throw new Error(err.MEL_EXN_ID, {
+                    cause: err
+                  });
         }
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       if (err.MEL_EXN_ID !== Stdlib__Parsing.Parse_error && err.MEL_EXN_ID !== Escape_error) {
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       
     }
@@ -25670,14 +26068,15 @@ function wrap$1(parsing_fun, lexbuf) {
     if (input_name.contents === "//toplevel//") {
       maybe_skip_phrase(lexbuf);
     }
-    throw {
-          MEL_EXN_ID: $$Error$3,
-          _1: {
-            TAG: /* Other */5,
-            _0: loc
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$3, {
+              cause: {
+                MEL_EXN_ID: $$Error$3,
+                _1: {
+                  TAG: /* Other */5,
+                  _0: loc
+                }
+              }
+            });
   }
 }
 
@@ -25860,7 +26259,9 @@ function alpha_pat(env, p) {
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
               tmp = /* Tpat_any */0;
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
           return {
@@ -25893,7 +26294,9 @@ function alpha_pat(env, p) {
             if (exn$1.MEL_EXN_ID === Stdlib.Not_found) {
               return new_p;
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
       default:
         
@@ -27498,7 +27901,9 @@ catch (raw_exn$2){
   if (exn$3.MEL_EXN_ID === Stdlib.Not_found) {
     need_to_clear_env = true;
   } else {
-    throw exn$3;
+    throw new Error(exn$3.MEL_EXN_ID, {
+              cause: exn$3
+            });
   }
 }
 
@@ -28031,15 +28436,16 @@ function is_object_type(path) {
         name = path._1;
         break;
     case /* Papply */2 :
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                30161,
-                23
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      30161,
+                      23
+                    ]
+                  }
+                });
     
   }
   return Caml_string.get(name, 0) === /* '#' */35;
@@ -28173,7 +28579,9 @@ function set_mode_pattern(generate, injective, f) {
     umode.contents = old_unification_mode;
     generate_equations.contents = old_gen;
     assume_injective.contents = old_inj;
-    throw e;
+    throw new Error(e.MEL_EXN_ID, {
+              cause: e
+            });
   }
 }
 
@@ -28201,7 +28609,9 @@ function in_pervasives(p) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -28217,28 +28627,30 @@ function is_datatype(decl) {
 function object_fields(ty) {
   var match = repr(ty).desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            30296,
-            27
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  30296,
+                  27
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tobject */4) {
     return match._0;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          30296,
-          27
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                30296,
+                27
+              ]
+            }
+          });
 }
 
 function flatten_fields(ty) {
@@ -28427,15 +28839,16 @@ function concrete_object(ty) {
 function close_object(ty) {
   var match = repr(ty).desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            30363,
-            25
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  30363,
+                  25
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tobject */4) {
     var _ty = match._0;
@@ -28444,15 +28857,16 @@ function close_object(ty) {
       var ty$2 = repr(ty$1);
       var match$1 = ty$2.desc;
       if (typeof match$1 === "number") {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                30359,
-                30
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      30359,
+                      30
+                    ]
+                  }
+                });
       }
       switch (match$1.TAG | 0) {
         case /* Tvar */0 :
@@ -28461,41 +28875,44 @@ function close_object(ty) {
             _ty = match$1._3;
             continue ;
         default:
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  30359,
-                  30
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        30359,
+                        30
+                      ]
+                    }
+                  });
       }
     };
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          30363,
-          25
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                30363,
+                25
+              ]
+            }
+          });
 }
 
 function row_variable(ty) {
   var match = repr(ty).desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            30377,
-            23
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  30377,
+                  23
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tobject */4) {
     var _ty = match._0;
@@ -28504,15 +28921,16 @@ function row_variable(ty) {
       var ty$2 = repr(ty$1);
       var match$1 = ty$2.desc;
       if (typeof match$1 === "number") {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                30373,
-                30
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      30373,
+                      30
+                    ]
+                  }
+                });
       }
       switch (match$1.TAG | 0) {
         case /* Tvar */0 :
@@ -28521,41 +28939,44 @@ function row_variable(ty) {
             _ty = match$1._3;
             continue ;
         default:
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  30373,
-                  30
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        30373,
+                        30
+                      ]
+                    }
+                  });
       }
     };
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          30377,
-          23
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                30377,
+                23
+              ]
+            }
+          });
 }
 
 function set_object_name(id, rv, params, ty) {
   var match = repr(ty).desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            30387,
-            6
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  30387,
+                  6
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tobject */4) {
     return set_name(match._1, [
@@ -28569,29 +28990,31 @@ function set_object_name(id, rv, params, ty) {
                 }
               ]);
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          30387,
-          6
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                30387,
+                6
+              ]
+            }
+          });
 }
 
 function hide_private_methods(ty) {
   var match = repr(ty).desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            30409,
-            6
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  30409,
+                  6
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tobject */4) {
     match._1.contents = undefined;
@@ -28605,15 +29028,16 @@ function hide_private_methods(ty) {
                   }
                 }), match$1[0]);
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          30409,
-          6
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                30409,
+                6
+              ]
+            }
+          });
 }
 
 function signature_of_class_type(_param) {
@@ -28787,10 +29211,11 @@ function closed_schema_rec(_ty) {
     switch (row.TAG | 0) {
       case /* Tvar */0 :
           if (level !== 100000000) {
-            throw {
-                  MEL_EXN_ID: Non_closed0,
-                  Error: new Error()
-                };
+            throw new Error(Non_closed0, {
+                      cause: {
+                        MEL_EXN_ID: Non_closed0
+                      }
+                    });
           }
           return iter_type_expr(closed_schema_rec, ty$1);
       case /* Tfield */5 :
@@ -28825,7 +29250,9 @@ function closed_schema(ty) {
       unmark_type(ty);
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -28887,7 +29314,9 @@ function free_vars_rec(_real, _ty) {
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID !== Stdlib.Not_found) {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
             
           }
@@ -28946,12 +29375,13 @@ function closed_type(ty) {
     return ;
   }
   var match$1 = match.hd;
-  throw {
-        MEL_EXN_ID: Non_closed,
-        _1: match$1[0],
-        _2: match$1[1],
-        Error: new Error()
-      };
+  throw new Error(Non_closed, {
+            cause: {
+              MEL_EXN_ID: Non_closed,
+              _1: match$1[0],
+              _2: match$1[1]
+            }
+          });
 }
 
 function closed_parameterized_type(params, ty) {
@@ -28966,7 +29396,9 @@ function closed_parameterized_type(params, ty) {
     if (exn.MEL_EXN_ID === Non_closed) {
       ok = false;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   Stdlib__List.iter(unmark_type, params);
@@ -29006,7 +29438,9 @@ function closed_type_decl(decl) {
       it_type_declaration(unmark_iterators, decl);
       return exn._1;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -29028,7 +29462,9 @@ function closed_extension_constructor(ext) {
       unmark_extension_constructor(ext);
       return exn._1;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -29059,19 +29495,22 @@ function closed_class(params, sign) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Non_closed) {
-                throw {
-                      MEL_EXN_ID: CCFailure,
-                      _1: {
-                        TAG: /* CC_Method */0,
-                        _0: exn._1,
-                        _1: exn._2,
-                        _2: param[0],
-                        _3: ty
-                      },
-                      Error: new Error()
-                    };
+                throw new Error(CCFailure, {
+                          cause: {
+                            MEL_EXN_ID: CCFailure,
+                            _1: {
+                              TAG: /* CC_Method */0,
+                              _0: exn._1,
+                              _1: exn._2,
+                              _2: param[0],
+                              _3: ty
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }), fields);
     iter_type_expr(mark_type, repr(sign.csig_self));
@@ -29087,7 +29526,9 @@ function closed_class(params, sign) {
       unmark_class_signature(sign);
       return exn._1;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -29195,10 +29636,11 @@ function generalize_spine(_ty) {
 
 var forward_try_expand_once = {
   contents: (function (env, ty) {
-      throw {
-            MEL_EXN_ID: Cannot_expand,
-            Error: new Error()
-          };
+      throw new Error(Cannot_expand, {
+                cause: {
+                  MEL_EXN_ID: Cannot_expand
+                }
+              });
     })
 };
 
@@ -29216,7 +29658,9 @@ function get_level(env, p) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return binding_time(p);
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -29232,7 +29676,9 @@ function normalize_package_path(env, _p) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         t = undefined;
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
     if (t === undefined) {
@@ -29255,20 +29701,21 @@ function update_level(env, level, _ty) {
     }
     var lv = gadt_instance_level(env, ty$1);
     if (lv !== undefined && level < lv) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: {
-              hd: [
-                ty$1,
-                newty2(level, {
-                      TAG: /* Tvar */0,
-                      _0: undefined
-                    })
-              ],
-              tl: /* [] */0
-            },
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: {
+                    hd: [
+                      ty$1,
+                      newty2(level, {
+                            TAG: /* Tvar */0,
+                            _0: undefined
+                          })
+                    ],
+                    tl: /* [] */0
+                  }
+                }
+              });
     }
     var row = ty$1.desc;
     if (typeof row !== "number") {
@@ -29284,26 +29731,29 @@ function update_level(env, level, _ty) {
                 var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                 if (exn.MEL_EXN_ID === Cannot_expand) {
                   if (level < get_level(env, p)) {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: {
-                            hd: [
-                              ty$1,
-                              newty2(level, {
-                                    TAG: /* Tvar */0,
-                                    _0: undefined
-                                  })
-                            ],
-                            tl: /* [] */0
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: {
+                                  hd: [
+                                    ty$1,
+                                    newty2(level, {
+                                          TAG: /* Tvar */0,
+                                          _0: undefined
+                                        })
+                                  ],
+                                  tl: /* [] */0
+                                }
+                              }
+                            });
                   }
                   return iter_type_expr((function (param) {
                                 return update_level(env, level, param);
                               }), ty$1);
                 }
-                throw exn;
+                throw new Error(exn.MEL_EXN_ID, {
+                          cause: exn
+                        });
               }
             }
             break;
@@ -29319,20 +29769,21 @@ function update_level(env, level, _ty) {
         case /* Tfield */5 :
             var ty1 = row._2;
             if (row._0 === dummy_method && repr(ty1).level > level) {
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: {
-                      hd: [
-                        ty1,
-                        newty2(level, {
-                              TAG: /* Tvar */0,
-                              _0: undefined
-                            })
-                      ],
-                      tl: /* [] */0
-                    },
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: {
+                            hd: [
+                              ty1,
+                              newty2(level, {
+                                    TAG: /* Tvar */0,
+                                    _0: undefined
+                                  })
+                            ],
+                            tl: /* [] */0
+                          }
+                        }
+                      });
             }
             break;
         case /* Tvariant */8 :
@@ -29361,20 +29812,21 @@ function update_level(env, level, _ty) {
             if (level < get_level(env, p$1)) {
               var p$p = normalize_package_path(env, p$1);
               if (same(p$1, p$p)) {
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: {
-                        hd: [
-                          ty$1,
-                          newty2(level, {
-                                TAG: /* Tvar */0,
-                                _0: undefined
-                              })
-                        ],
-                        tl: /* [] */0
-                      },
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: {
+                              hd: [
+                                ty$1,
+                                newty2(level, {
+                                      TAG: /* Tvar */0,
+                                      _0: undefined
+                                    })
+                              ],
+                              tl: /* [] */0
+                            }
+                          }
+                        });
               }
               log_type(ty$1);
               ty$1.desc = {
@@ -29443,7 +29895,9 @@ function generalize_expansive(env, var_level, _ty) {
                       return Types_Variance.may_inv;
                     }), tyl);
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
           match._2.contents = /* Mnil */0;
@@ -29480,23 +29934,30 @@ function generalize_expansive$1(env, ty) {
       var tr = exn._1;
       if (tr) {
         if (tr.tl) {
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
-        throw {
-              MEL_EXN_ID: Unify,
-              _1: {
-                hd: [
-                  ty,
-                  tr.hd[1]
-                ],
-                tl: tr
-              },
-              Error: new Error()
-            };
+        throw new Error(Unify, {
+                  cause: {
+                    MEL_EXN_ID: Unify,
+                    _1: {
+                      hd: [
+                        ty,
+                        tr.hd[1]
+                      ],
+                      tl: tr
+                    }
+                  }
+                });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -29605,7 +30066,9 @@ function inv_type(hash, pty, ty) {
                     return inv_type(hash, partial_arg, param);
                   }), ty$1);
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -29639,7 +30102,9 @@ function compute_univars(ty) {
                       return add_univar(univ, param);
                     }), inv.inv_parents);
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   Curry._2(TypeHash.iter, (function (ty, inv) {
@@ -29657,7 +30122,9 @@ function compute_univars(ty) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         return /* Empty */0;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
 }
@@ -29718,15 +30185,16 @@ function copy(env, partial, keep_names, ty) {
           partial[1] ? ty$1.level : current_level.contents
         ) : 100000000;
     } else {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              30996,
-              16
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    30996,
+                    16
+                  ]
+                }
+              });
     }
     if (forget !== 100000000) {
       return newty2(forget, {
@@ -29865,15 +30333,16 @@ function copy(env, partial, keep_names, ty) {
                       exit$3 = 4;
                       break;
                   default:
-                    throw {
-                          MEL_EXN_ID: "Assert_failure",
-                          _1: [
-                            "jscomp/test/ocaml_typedtree_test.ml",
-                            31059,
-                            24
-                          ],
-                          Error: new Error()
-                        };
+                    throw new Error("Assert_failure", {
+                              cause: {
+                                MEL_EXN_ID: "Assert_failure",
+                                _1: [
+                                  "jscomp/test/ocaml_typedtree_test.ml",
+                                  31059,
+                                  24
+                                ]
+                              }
+                            });
                 }
               }
               switch (exit$3) {
@@ -30021,7 +30490,9 @@ function get_new_abstract_name(s) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       index = 0;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   reified_var_counter.contents = Curry._3(Meths.add, s, index, reified_var_counter.contents);
@@ -30092,15 +30563,16 @@ function instance_constructor(in_pattern, cstr) {
           });
       var tv = copy(undefined, undefined, undefined, existential);
       if (!is_Tvar(tv)) {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                31182,
-                8
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      31182,
+                      8
+                    ]
+                  }
+                });
       }
       link_type(tv, to_unify);
     };
@@ -30242,11 +30714,12 @@ function diff_list(l1, l2) {
             tl: diff_list(l1.tl, l2)
           };
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Ctype.diff_list",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Ctype.diff_list"
+            }
+          });
 }
 
 function conflicts(free, bound) {
@@ -30286,10 +30759,11 @@ function copy_sep(fixed, free, bound, visited, ty) {
     var match = Stdlib__List.assq(ty$1, visited);
     var dl = is_Tunivar(ty$1) ? /* [] */0 : diff_list(bound, match[1]);
     if (Caml_obj.caml_notequal(dl, /* [] */0) && conflicts(univars, dl)) {
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
     return match[0];
   }
@@ -30377,7 +30851,9 @@ function copy_sep(fixed, free, bound, visited, ty) {
       t$1.desc = tmp;
       return t$1;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -30387,15 +30863,16 @@ function instance_poly(keep_namesOpt, fixed, univars, sch) {
   var copy_var = function (ty) {
     var name = ty.desc;
     if (typeof name === "number") {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              31319,
-              11
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    31319,
+                    11
+                  ]
+                }
+              });
     }
     if (name.TAG === /* Tunivar */9) {
       if (keep_names) {
@@ -30407,15 +30884,16 @@ function instance_poly(keep_namesOpt, fixed, univars, sch) {
         return newvar(undefined, undefined);
       }
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            31319,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  31319,
+                  11
+                ]
+              }
+            });
   };
   var vars = Stdlib__List.map(copy_var, univars$1);
   var pairs = Stdlib__List.map2((function (u, v) {
@@ -30465,21 +30943,23 @@ function instance_label(fixed, lbl) {
 
 var unify$p = {
   contents: (function (env, ty1, ty2) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     })
 };
 
 function subst(env, level, priv, abbrev, ty, params, args, body) {
   if (Stdlib__List.length(params) !== Stdlib__List.length(args)) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   var old_level = current_level.contents;
   current_level.contents = level;
@@ -30488,30 +30968,32 @@ function subst(env, level, priv, abbrev, ty, params, args, body) {
     if (ty !== undefined) {
       var match = ty.desc;
       if (typeof match === "number") {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                31359,
-                8
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      31359,
+                      8
+                    ]
+                  }
+                });
       }
       if (match.TAG === /* Tconstr */3) {
         var path = match._0;
         var abbrev$1 = proper_abbrevs(path, match._1, abbrev);
         memorize_abbrev(abbrev$1, priv, path, ty, body0);
       } else {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                31359,
-                8
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      31359,
+                      8
+                    ]
+                  }
+                });
       }
     }
     abbreviations.contents = abbrev;
@@ -30529,9 +31011,13 @@ function subst(env, level, priv, abbrev, ty, params, args, body) {
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
       current_level.contents = old_level;
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -30552,15 +31038,16 @@ function expand_abbrev_gen(kind, find_type_expansion, env, ty) {
   check_abbrev_env(env);
   var match = ty.desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            31468,
-            6
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  31468,
+                  6
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tconstr */3) {
     var abbrev = match._2;
@@ -30577,7 +31064,9 @@ function expand_abbrev_gen(kind, find_type_expansion, env, ty) {
         catch (raw_exn){
           var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
           if (exn.MEL_EXN_ID !== Unify) {
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           
         }
@@ -30591,12 +31080,15 @@ function expand_abbrev_gen(kind, find_type_expansion, env, ty) {
     catch (raw_exn$1){
       var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
       if (exn$1.MEL_EXN_ID === Stdlib.Not_found) {
-        throw {
-              MEL_EXN_ID: Cannot_expand,
-              Error: new Error()
-            };
+        throw new Error(Cannot_expand, {
+                  cause: {
+                    MEL_EXN_ID: Cannot_expand
+                  }
+                });
       }
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
     var ty$p = subst(env, level, kind, abbrev, ty, match$1[0], args, match$1[1]);
     var ty$2 = repr(ty$p);
@@ -30625,20 +31117,21 @@ function expand_abbrev_gen(kind, find_type_expansion, env, ty) {
       var lv = Caml_obj.caml_max(match$1[2], gadt_instance_level(env, ty));
       if (lv !== undefined) {
         if (level < lv) {
-          throw {
-                MEL_EXN_ID: Unify,
-                _1: {
-                  hd: [
-                    ty,
-                    newty2(level, {
-                          TAG: /* Tvar */0,
-                          _0: undefined
-                        })
-                  ],
-                  tl: /* [] */0
-                },
-                Error: new Error()
-              };
+          throw new Error(Unify, {
+                    cause: {
+                      MEL_EXN_ID: Unify,
+                      _1: {
+                        hd: [
+                          ty,
+                          newty2(level, {
+                                TAG: /* Tvar */0,
+                                _0: undefined
+                              })
+                        ],
+                        tl: /* [] */0
+                      }
+                    }
+                  });
         }
         add_gadt_instances(env, lv, {
               hd: ty,
@@ -30652,15 +31145,16 @@ function expand_abbrev_gen(kind, find_type_expansion, env, ty) {
     }
     return ty$p;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          31468,
-          6
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                31468,
+                6
+              ]
+            }
+          });
 }
 
 function expand_abbrev(ty) {
@@ -30676,17 +31170,20 @@ function expand_head_once(env, ty) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Cannot_expand) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              31476,
-              56
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    31476,
+                    56
+                  ]
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -30706,7 +31203,9 @@ function safe_abbrev(env, ty) {
       backtrack(snap);
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -30714,18 +31213,20 @@ function try_expand_once(env, ty) {
   var ty$1 = repr(ty);
   var match = ty$1.desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: Cannot_expand,
-          Error: new Error()
-        };
+    throw new Error(Cannot_expand, {
+              cause: {
+                MEL_EXN_ID: Cannot_expand
+              }
+            });
   }
   if (match.TAG === /* Tconstr */3) {
     return repr(expand_abbrev(env)(ty$1));
   }
-  throw {
-        MEL_EXN_ID: Cannot_expand,
-        Error: new Error()
-      };
+  throw new Error(Cannot_expand, {
+            cause: {
+              MEL_EXN_ID: Cannot_expand
+            }
+          });
 }
 
 function try_expand_safe(env, ty) {
@@ -30737,12 +31238,15 @@ function try_expand_safe(env, ty) {
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
       backtrack(snap);
-      throw {
-            MEL_EXN_ID: Cannot_expand,
-            Error: new Error()
-          };
+      throw new Error(Cannot_expand, {
+                cause: {
+                  MEL_EXN_ID: Cannot_expand
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -30756,7 +31260,9 @@ function try_expand_head(try_once, env, ty) {
     if (exn.MEL_EXN_ID === Cannot_expand) {
       return ty$p;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -30778,7 +31284,9 @@ function expand_head_unif(env, ty) {
     if (exn.MEL_EXN_ID === Cannot_expand) {
       return repr(ty);
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -30791,7 +31299,9 @@ function expand_head(env, ty) {
     if (exn.MEL_EXN_ID === Cannot_expand) {
       return repr(ty);
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -30801,10 +31311,11 @@ function extract_concrete_typedecl(env, ty) {
   var ty$1 = repr(ty);
   var match = ty$1.desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   if (match.TAG === /* Tconstr */3) {
     var p = match._0;
@@ -30823,12 +31334,15 @@ function extract_concrete_typedecl(env, ty) {
     catch (raw_exn){
       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
       if (exn.MEL_EXN_ID === Cannot_expand) {
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
     var match$1 = extract_concrete_typedecl(env, ty$2);
     return [
@@ -30837,10 +31351,11 @@ function extract_concrete_typedecl(env, ty) {
             match$1[2]
           ];
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function expand_abbrev_opt(param, param$1) {
@@ -30851,18 +31366,20 @@ function try_expand_once_opt(env, ty) {
   var ty$1 = repr(ty);
   var match = ty$1.desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: Cannot_expand,
-          Error: new Error()
-        };
+    throw new Error(Cannot_expand, {
+              cause: {
+                MEL_EXN_ID: Cannot_expand
+              }
+            });
   }
   if (match.TAG === /* Tconstr */3) {
     return repr(expand_abbrev_opt(env, ty$1));
   }
-  throw {
-        MEL_EXN_ID: Cannot_expand,
-        Error: new Error()
-      };
+  throw new Error(Cannot_expand, {
+            cause: {
+              MEL_EXN_ID: Cannot_expand
+            }
+          });
 }
 
 function try_expand_head_opt(env, ty) {
@@ -30875,7 +31392,9 @@ function try_expand_head_opt(env, ty) {
     if (exn.MEL_EXN_ID === Cannot_expand) {
       return ty$p;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -30894,22 +31413,25 @@ function expand_head_opt(env, ty) {
       backtrack(snap);
       return repr(ty);
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
 function enforce_constraints(env, ty) {
   var match = ty.desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            31586,
-            6
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  31586,
+                  6
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tconstr */3) {
     var level = ty.level;
@@ -30928,18 +31450,21 @@ function enforce_constraints(env, ty) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         return ;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   } else {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            31586,
-            6
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  31586,
+                  6
+                ]
+              }
+            });
   }
 }
 
@@ -30980,7 +31505,9 @@ function generic_abbrev(env, path) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31009,7 +31536,9 @@ function generic_private_abbrev(env, path) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31033,7 +31562,9 @@ function is_contractive(env, ty) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31041,10 +31572,11 @@ var Occur = /* @__PURE__ */Caml_exceptions.create("Ocaml_typedtree_test.Ctype.Oc
 
 function occur_rec(env, visited, ty0, ty) {
   if (ty === ty0) {
-    throw {
-          MEL_EXN_ID: Occur,
-          Error: new Error()
-        };
+    throw new Error(Occur, {
+              cause: {
+                MEL_EXN_ID: Occur
+              }
+            });
   }
   var occur_ok = recursive_types.contents && is_contractive(env, ty);
   var match = ty.desc;
@@ -31053,10 +31585,11 @@ function occur_rec(env, visited, ty0, ty) {
       case /* Tconstr */3 :
           try {
             if (occur_ok || Stdlib__List.memq(ty, visited)) {
-              throw {
-                    MEL_EXN_ID: Occur,
-                    Error: new Error()
-                  };
+              throw new Error(Occur, {
+                        cause: {
+                          MEL_EXN_ID: Occur
+                        }
+                      });
             }
             var partial_arg = {
               hd: ty,
@@ -31072,10 +31605,11 @@ function occur_rec(env, visited, ty0, ty) {
               try {
                 var ty$p = try_expand_head$1(try_expand_once, env, ty);
                 if (ty$p === ty0 || Stdlib__List.memq(ty$p, visited)) {
-                  throw {
-                        MEL_EXN_ID: Occur,
-                        Error: new Error()
-                      };
+                  throw new Error(Occur, {
+                            cause: {
+                              MEL_EXN_ID: Occur
+                            }
+                          });
                 }
                 var match$1 = ty$p.desc;
                 var exit = 0;
@@ -31110,15 +31644,20 @@ function occur_rec(env, visited, ty0, ty) {
                   if (occur_ok) {
                     return ;
                   }
-                  throw {
-                        MEL_EXN_ID: Occur,
-                        Error: new Error()
-                      };
+                  throw new Error(Occur, {
+                            cause: {
+                              MEL_EXN_ID: Occur
+                            }
+                          });
                 }
-                throw exn$1;
+                throw new Error(exn$1.MEL_EXN_ID, {
+                          cause: exn$1
+                        });
               }
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
           break;
@@ -31160,10 +31699,17 @@ function occur(env, ty0, ty) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     merge$2(type_changed, old);
-    throw exn.MEL_EXN_ID === Occur ? ({
-              MEL_EXN_ID: Unify,
-              _1: /* [] */0
-            }) : exn;
+    throw new Error((
+              exn.MEL_EXN_ID === Occur ? ({
+                    MEL_EXN_ID: Unify,
+                    _1: /* [] */0
+                  }) : exn
+            ).MEL_EXN_ID, {
+              cause: exn.MEL_EXN_ID === Occur ? ({
+                    MEL_EXN_ID: Unify,
+                    _1: /* [] */0
+                  }) : exn
+            });
   }
 }
 
@@ -31177,7 +31723,9 @@ function occur_in(env, ty0, t) {
     if (exn.MEL_EXN_ID === Unify) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31198,7 +31746,9 @@ function unify_univar(t1, t2, _param) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             return ;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
       };
       var match$1 = find_univ(t1, match[0]);
@@ -31210,51 +31760,57 @@ function unify_univar(t1, t2, _param) {
             if (t2 === repr(t$p2)) {
               return ;
             }
-            throw {
-                  MEL_EXN_ID: Unify,
-                  _1: /* [] */0,
-                  Error: new Error()
-                };
+            throw new Error(Unify, {
+                      cause: {
+                        MEL_EXN_ID: Unify,
+                        _1: /* [] */0
+                      }
+                    });
           }
-          throw {
-                MEL_EXN_ID: Unify,
-                _1: /* [] */0,
-                Error: new Error()
-              };
+          throw new Error(Unify, {
+                    cause: {
+                      MEL_EXN_ID: Unify,
+                      _1: /* [] */0
+                    }
+                  });
         }
         if (match$2 !== undefined) {
           var match$3 = match$2.contents;
           if (match$3 !== undefined) {
-            throw {
-                  MEL_EXN_ID: Unify,
-                  _1: /* [] */0,
-                  Error: new Error()
-                };
+            throw new Error(Unify, {
+                      cause: {
+                        MEL_EXN_ID: Unify,
+                        _1: /* [] */0
+                      }
+                    });
           }
           set_univar(match$1, t2);
           return set_univar(match$2, t1);
         }
-        throw {
-              MEL_EXN_ID: Unify,
-              _1: /* [] */0,
-              Error: new Error()
-            };
+        throw new Error(Unify, {
+                  cause: {
+                    MEL_EXN_ID: Unify,
+                    _1: /* [] */0
+                  }
+                });
       }
       if (match$2 !== undefined) {
-        throw {
-              MEL_EXN_ID: Unify,
-              _1: /* [] */0,
-              Error: new Error()
-            };
+        throw new Error(Unify, {
+                  cause: {
+                    MEL_EXN_ID: Unify,
+                    _1: /* [] */0
+                  }
+                });
       }
       _param = param.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   };
 }
 
@@ -31293,7 +31849,9 @@ function occur_univar(env, ty) {
               visited.contents = Curry._3(add$4, ty$1, bound, visited.contents);
               tmp$1 = true;
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
         }
@@ -31336,26 +31894,29 @@ function occur_univar(env, ty) {
                           }
                           }(bound)), tl);
               }
-              throw exn$1;
+              throw new Error(exn$1.MEL_EXN_ID, {
+                        cause: exn$1
+                      });
             }
         case /* Tunivar */9 :
             if (Curry._2(mem$3, ty$1, bound)) {
               return ;
             }
-            throw {
-                  MEL_EXN_ID: Unify,
-                  _1: {
-                    hd: [
-                      ty$1,
-                      newty2(100000000, {
-                            TAG: /* Tvar */0,
-                            _0: undefined
-                          })
-                    ],
-                    tl: /* [] */0
-                  },
-                  Error: new Error()
-                };
+            throw new Error(Unify, {
+                      cause: {
+                        MEL_EXN_ID: Unify,
+                        _1: {
+                          hd: [
+                            ty$1,
+                            newty2(100000000, {
+                                  TAG: /* Tvar */0,
+                                  _0: undefined
+                                })
+                          ],
+                          tl: /* [] */0
+                        }
+                      }
+                    });
         case /* Tpoly */10 :
             var bound$1 = Stdlib__List.fold_right(add$3, Stdlib__List.map(repr, match._1), bound);
             _ty = match._0;
@@ -31376,7 +31937,9 @@ function occur_univar(env, ty) {
   }
   catch (exn){
     unmark_type(ty);
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31441,16 +32004,19 @@ function univars_escape(env, univar_pairs, vl, ty) {
               if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                 return Stdlib__List.iter(occur, tl);
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
         case /* Tunivar */9 :
             if (!Curry._2(mem$3, t$1, family)) {
               return ;
             }
-            throw {
-                  MEL_EXN_ID: Occur,
-                  Error: new Error()
-                };
+            throw new Error(Occur, {
+                      cause: {
+                        MEL_EXN_ID: Occur
+                      }
+                    });
         case /* Tpoly */10 :
             if (Stdlib__List.exists((function (t) {
                       return Curry._2(mem$3, repr(t), family);
@@ -31473,7 +32039,9 @@ function univars_escape(env, univar_pairs, vl, ty) {
     if (exn.MEL_EXN_ID === Occur) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31497,11 +32065,12 @@ function enter_poly(env, univar_pairs, t1, tl1, t2, tl2, f) {
               _0: t1,
               _1: tl1$1
             }))) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   var cl1 = Stdlib__List.map((function (t) {
           return [
@@ -31539,7 +32108,9 @@ function enter_poly(env, univar_pairs, t1, tl1, t2, tl2, f) {
   }
   catch (exn){
     univar_pairs.contents = old_univars;
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31610,10 +32181,11 @@ function deep_occur(t0, ty) {
       return ;
     }
     if (ty$1 === t0) {
-      throw {
-            MEL_EXN_ID: Occur,
-            Error: new Error()
-          };
+      throw new Error(Occur, {
+                cause: {
+                  MEL_EXN_ID: Occur
+                }
+              });
     }
     ty$1.level = pivot_level - ty$1.level | 0;
     iter_type_expr(occur_rec, ty$1);
@@ -31629,7 +32201,9 @@ function deep_occur(t0, ty) {
       unmark_type(ty);
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31642,15 +32216,16 @@ function get_newtype_level(param) {
   if (x !== undefined) {
     return x;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          31961,
-          12
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                31961,
+                12
+              ]
+            }
+          });
 }
 
 function reify(env, t) {
@@ -31710,15 +32285,16 @@ function reify(env, t) {
               var m = r.row_more;
               var o$2 = m.desc;
               if (typeof o$2 === "number") {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        31999,
-                        19
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              31999,
+                              19
+                            ]
+                          }
+                        });
               }
               if (o$2.TAG === /* Tvar */0) {
                 var o$3 = o$2._0;
@@ -31740,15 +32316,16 @@ function reify(env, t) {
                           _0: row
                         }));
               } else {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        31999,
-                        19
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              31999,
+                              19
+                            ]
+                          }
+                        });
               }
             }
           }
@@ -31774,7 +32351,9 @@ function is_newtype(env, p) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31810,7 +32389,9 @@ function expands_to_datatype(env, ty) {
     if (exn.MEL_EXN_ID === Cannot_expand) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -31908,52 +32489,57 @@ function mcomp(type_pairs, env, _t1, _t2) {
             if (match$3.TAG === /* Tconstr */3) {
               exit$3 = 3;
             } else {
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: /* [] */0,
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: /* [] */0
+                        }
+                      });
             }
           } else {
             switch (match$2.TAG | 0) {
               case /* Tvar */0 :
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   switch (match$3.TAG | 0) {
                     case /* Tvar */0 :
-                        throw {
-                              MEL_EXN_ID: "Assert_failure",
-                              _1: [
-                                "jscomp/test/ocaml_typedtree_test.ml",
-                                32063,
-                                30
-                              ],
-                              Error: new Error()
-                            };
+                        throw new Error("Assert_failure", {
+                                  cause: {
+                                    MEL_EXN_ID: "Assert_failure",
+                                    _1: [
+                                      "jscomp/test/ocaml_typedtree_test.ml",
+                                      32063,
+                                      30
+                                    ]
+                                  }
+                                });
                     case /* Tconstr */3 :
                         exit$3 = 3;
                         break;
                     default:
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                   }
                   break;
               case /* Tarrow */1 :
                   var l1 = match$2._0;
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   switch (match$3.TAG | 0) {
                     case /* Tarrow */1 :
@@ -31964,29 +32550,32 @@ function mcomp(type_pairs, env, _t1, _t2) {
                           _t1 = match$2._2;
                           continue ;
                         }
-                        throw {
-                              MEL_EXN_ID: Unify,
-                              _1: /* [] */0,
-                              Error: new Error()
-                            };
+                        throw new Error(Unify, {
+                                  cause: {
+                                    MEL_EXN_ID: Unify,
+                                    _1: /* [] */0
+                                  }
+                                });
                     case /* Tconstr */3 :
                         exit$3 = 3;
                         break;
                     default:
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                   }
                   break;
               case /* Ttuple */2 :
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   switch (match$3.TAG | 0) {
                     case /* Ttuple */2 :
@@ -31995,11 +32584,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                         exit$3 = 3;
                         break;
                     default:
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                   }
                   break;
               case /* Tconstr */3 :
@@ -32027,7 +32617,9 @@ function mcomp(type_pairs, env, _t1, _t2) {
                                       return false;
                                     }), tl1);
                             } else {
-                              throw exn$1;
+                              throw new Error(exn$1.MEL_EXN_ID, {
+                                        cause: exn$1
+                                      });
                             }
                           }
                           return Stdlib__List.iter2((function (i, param) {
@@ -32038,11 +32630,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                                       }), inj, Stdlib__List.combine(tl1, tl2));
                         }
                         if (non_aliasable(p1, decl) && non_aliasable(p2, decl$p)) {
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                         var match$4 = decl.type_kind;
                         var match$5 = decl$p.type_kind;
@@ -32071,22 +32664,24 @@ function mcomp(type_pairs, env, _t1, _t2) {
                             }
                             exit$4 = 1;
                           } else {
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                         } else if (match$4.TAG === /* Type_record */0) {
                           if (typeof match$5 === "number") {
                             if (match$5 === /* Type_abstract */0) {
                               exit$4 = 1;
                             } else {
-                              throw {
-                                    MEL_EXN_ID: Unify,
-                                    _1: /* [] */0,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Unify, {
+                                        cause: {
+                                          MEL_EXN_ID: Unify,
+                                          _1: /* [] */0
+                                        }
+                                      });
                             }
                           } else {
                             if (match$5.TAG === /* Type_record */0) {
@@ -32094,35 +32689,39 @@ function mcomp(type_pairs, env, _t1, _t2) {
                                 mcomp_list(type_pairs, env, tl1, tl2);
                                 return mcomp_record_description(type_pairs, env)(match$4._0, match$5._0);
                               }
-                              throw {
-                                    MEL_EXN_ID: Unify,
-                                    _1: /* [] */0,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Unify, {
+                                        cause: {
+                                          MEL_EXN_ID: Unify,
+                                          _1: /* [] */0
+                                        }
+                                      });
                             }
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                         } else if (typeof match$5 === "number") {
                           if (match$5 === /* Type_abstract */0) {
                             exit$4 = 1;
                           } else {
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                         } else {
                           if (match$5.TAG === /* Type_record */0) {
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           mcomp_list(type_pairs, env, tl1, tl2);
                           var xs = match$4._0;
@@ -32143,51 +32742,57 @@ function mcomp(type_pairs, env, _t1, _t2) {
                                   _x = x.tl;
                                   continue ;
                                 }
-                                throw {
-                                      MEL_EXN_ID: Unify,
-                                      _1: /* [] */0,
-                                      Error: new Error()
-                                    };
+                                throw new Error(Unify, {
+                                          cause: {
+                                            MEL_EXN_ID: Unify,
+                                            _1: /* [] */0
+                                          }
+                                        });
                               }
-                              throw {
-                                    MEL_EXN_ID: Unify,
-                                    _1: /* [] */0,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Unify, {
+                                        cause: {
+                                          MEL_EXN_ID: Unify,
+                                          _1: /* [] */0
+                                        }
+                                      });
                             }
                             if (!y) {
                               return ;
                             }
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           };
                         }
                         if (exit$4 === 1) {
                           if (typeof match$5 === "number") {
                             if (match$5) {
-                              throw {
-                                    MEL_EXN_ID: Unify,
-                                    _1: /* [] */0,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Unify, {
+                                        cause: {
+                                          MEL_EXN_ID: Unify,
+                                          _1: /* [] */0
+                                        }
+                                      });
                             }
                             if (!non_aliasable(p2, decl$p)) {
                               return ;
                             }
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                         
                       }
@@ -32196,7 +32801,9 @@ function mcomp(type_pairs, env, _t1, _t2) {
                         if (exn$2.MEL_EXN_ID === Stdlib.Not_found) {
                           return ;
                         }
-                        throw exn$2;
+                        throw new Error(exn$2.MEL_EXN_ID, {
+                                  cause: exn$2
+                                });
                       }
                     }
                     p = p1;
@@ -32205,11 +32812,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                   break;
               case /* Tobject */4 :
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   switch (match$3.TAG | 0) {
                     case /* Tconstr */3 :
@@ -32218,20 +32826,22 @@ function mcomp(type_pairs, env, _t1, _t2) {
                     case /* Tobject */4 :
                         return mcomp_fields(type_pairs, env, match$2._0, match$3._0);
                     default:
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                   }
                   break;
               case /* Tfield */5 :
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   switch (match$3.TAG | 0) {
                     case /* Tconstr */3 :
@@ -32240,11 +32850,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                     case /* Tfield */5 :
                         return mcomp_fields(type_pairs, env, t1$p$1, t2$p$1);
                     default:
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                   }
                   break;
               case /* Tlink */6 :
@@ -32253,11 +32864,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                   break;
               case /* Tvariant */8 :
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   switch (match$3.TAG | 0) {
                     case /* Tconstr */3 :
@@ -32278,11 +32890,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                           }
                         };
                         if (row1$1.row_closed && Stdlib__List.exists(cannot_erase, match$6[1]) || row2$1.row_closed && Stdlib__List.exists(cannot_erase, match$6[0])) {
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                         return Stdlib__List.iter((function (param) {
                                       var match = row_field_repr_aux(/* [] */0, param[1]);
@@ -32295,59 +32908,65 @@ function mcomp(type_pairs, env, _t1, _t2) {
                                         var t1 = match._0;
                                         if (t1 !== undefined) {
                                           if (typeof match$1 === "number") {
-                                            throw {
-                                                  MEL_EXN_ID: Unify,
-                                                  _1: /* [] */0,
-                                                  Error: new Error()
-                                                };
+                                            throw new Error(Unify, {
+                                                      cause: {
+                                                        MEL_EXN_ID: Unify,
+                                                        _1: /* [] */0
+                                                      }
+                                                    });
                                           }
                                           if (match$1.TAG === /* Rpresent */0) {
                                             var t2 = match$1._0;
                                             if (t2 !== undefined) {
                                               return mcomp(type_pairs, env, t1, t2);
                                             }
-                                            throw {
-                                                  MEL_EXN_ID: Unify,
-                                                  _1: /* [] */0,
-                                                  Error: new Error()
-                                                };
+                                            throw new Error(Unify, {
+                                                      cause: {
+                                                        MEL_EXN_ID: Unify,
+                                                        _1: /* [] */0
+                                                      }
+                                                    });
                                           }
                                           if (match$1._0) {
-                                            throw {
-                                                  MEL_EXN_ID: Unify,
-                                                  _1: /* [] */0,
-                                                  Error: new Error()
-                                                };
+                                            throw new Error(Unify, {
+                                                      cause: {
+                                                        MEL_EXN_ID: Unify,
+                                                        _1: /* [] */0
+                                                      }
+                                                    });
                                           }
                                           return Stdlib__List.iter((function (param) {
                                                         return mcomp(type_pairs, env, t1, param);
                                                       }), match$1._1);
                                         } else {
                                           if (typeof match$1 === "number") {
-                                            throw {
-                                                  MEL_EXN_ID: Unify,
-                                                  _1: /* [] */0,
-                                                  Error: new Error()
-                                                };
+                                            throw new Error(Unify, {
+                                                      cause: {
+                                                        MEL_EXN_ID: Unify,
+                                                        _1: /* [] */0
+                                                      }
+                                                    });
                                           }
                                           if (match$1.TAG === /* Rpresent */0) {
                                             if (match$1._0 === undefined) {
                                               return ;
                                             }
-                                            throw {
-                                                  MEL_EXN_ID: Unify,
-                                                  _1: /* [] */0,
-                                                  Error: new Error()
-                                                };
+                                            throw new Error(Unify, {
+                                                      cause: {
+                                                        MEL_EXN_ID: Unify,
+                                                        _1: /* [] */0
+                                                      }
+                                                    });
                                           }
                                           if (!match$1._1) {
                                             return ;
                                           }
-                                          throw {
-                                                MEL_EXN_ID: Unify,
-                                                _1: /* [] */0,
-                                                Error: new Error()
-                                              };
+                                          throw new Error(Unify, {
+                                                    cause: {
+                                                      MEL_EXN_ID: Unify,
+                                                      _1: /* [] */0
+                                                    }
+                                                  });
                                         }
                                       } else {
                                         var exit$2 = 0;
@@ -32381,11 +33000,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                                         if (match$1._0 !== undefined) {
                                           exit = 1;
                                         } else {
-                                          throw {
-                                                MEL_EXN_ID: Unify,
-                                                _1: /* [] */0,
-                                                Error: new Error()
-                                              };
+                                          throw new Error(Unify, {
+                                                    cause: {
+                                                      MEL_EXN_ID: Unify,
+                                                      _1: /* [] */0
+                                                    }
+                                                  });
                                         }
                                       }
                                       if (exit === 1) {
@@ -32408,31 +33028,34 @@ function mcomp(type_pairs, env, _t1, _t2) {
                                           if (match$1._0 === undefined) {
                                             return ;
                                           }
-                                          throw {
-                                                MEL_EXN_ID: Unify,
-                                                _1: /* [] */0,
-                                                Error: new Error()
-                                              };
+                                          throw new Error(Unify, {
+                                                    cause: {
+                                                      MEL_EXN_ID: Unify,
+                                                      _1: /* [] */0
+                                                    }
+                                                  });
                                         }
                                         
                                       }
                                       
                                     }), match$6[2]);
                     default:
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                   }
                   break;
               case /* Tunivar */9 :
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   switch (match$3.TAG | 0) {
                     case /* Tconstr */3 :
@@ -32441,11 +33064,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                     case /* Tunivar */9 :
                         return unify_univar(t1$p$1, t2$p$1, univar_pairs.contents);
                     default:
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                   }
                   break;
               case /* Tpoly */10 :
@@ -32456,11 +33080,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                     exit$6 = 4;
                   } else {
                     if (typeof match$3 === "number") {
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                     }
                     switch (match$3.TAG | 0) {
                       case /* Tconstr */3 :
@@ -32476,20 +33101,22 @@ function mcomp(type_pairs, env, _t1, _t2) {
                           }
                           break;
                       default:
-                        throw {
-                              MEL_EXN_ID: Unify,
-                              _1: /* [] */0,
-                              Error: new Error()
-                            };
+                        throw new Error(Unify, {
+                                  cause: {
+                                    MEL_EXN_ID: Unify,
+                                    _1: /* [] */0
+                                  }
+                                });
                     }
                   }
                   if (exit$6 === 4) {
                     if (typeof match$3 === "number") {
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                     }
                     switch (match$3.TAG | 0) {
                       case /* Tconstr */3 :
@@ -32500,21 +33127,23 @@ function mcomp(type_pairs, env, _t1, _t2) {
                                         return mcomp(type_pairs, env, param, param$1);
                                       }));
                       default:
-                        throw {
-                              MEL_EXN_ID: Unify,
-                              _1: /* [] */0,
-                              Error: new Error()
-                            };
+                        throw new Error(Unify, {
+                                  cause: {
+                                    MEL_EXN_ID: Unify,
+                                    _1: /* [] */0
+                                  }
+                                });
                     }
                   }
                   break;
               case /* Tpackage */11 :
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   switch (match$3.TAG | 0) {
                     case /* Tconstr */3 :
@@ -32523,11 +33152,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
                     case /* Tpackage */11 :
                         return ;
                     default:
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                   }
                   break;
               
@@ -32535,21 +33165,23 @@ function mcomp(type_pairs, env, _t1, _t2) {
           }
           if (exit$3 === 3) {
             if (typeof match$3 === "number") {
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: /* [] */0,
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: /* [] */0
+                        }
+                      });
             }
             if (match$3.TAG === /* Tconstr */3) {
               p = match$3._0;
               exit$2 = 2;
             } else {
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: /* [] */0,
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: /* [] */0
+                        }
+                      });
             }
           }
           if (exit$2 === 2) {
@@ -32558,23 +33190,28 @@ function mcomp(type_pairs, env, _t1, _t2) {
               if (!(non_aliasable(p, decl$1) || is_datatype(decl$1))) {
                 return ;
               }
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: /* [] */0,
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: /* [] */0
+                        }
+                      });
             }
             catch (raw_exn$3){
               var exn$3 = Caml_js_exceptions.internalToOCamlException(raw_exn$3);
               if (exn$3.MEL_EXN_ID === Stdlib.Not_found) {
                 return ;
               }
-              throw exn$3;
+              throw new Error(exn$3.MEL_EXN_ID, {
+                        cause: exn$3
+                      });
             }
           }
           
         } else {
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
       }
     }
@@ -32584,11 +33221,12 @@ function mcomp(type_pairs, env, _t1, _t2) {
 
 function mcomp_list(type_pairs, env, tl1, tl2) {
   if (Stdlib__List.length(tl1) !== Stdlib__List.length(tl2)) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   Stdlib__List.iter2((function (param, param$1) {
           return mcomp(type_pairs, env, param, param$1);
@@ -32597,26 +33235,28 @@ function mcomp_list(type_pairs, env, tl1, tl2) {
 
 function mcomp_fields(type_pairs, env, ty1, ty2) {
   if (!(concrete_object(ty1) && concrete_object(ty2))) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            32108,
-            59
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  32108,
+                  59
+                ]
+              }
+            });
   }
   var match = flatten_fields(ty2);
   var match$1 = flatten_fields(ty1);
   var match$2 = associate_fields(match$1[0], match[0]);
   mcomp(type_pairs, env, match$1[1], match[1]);
   if (Caml_obj.caml_notequal(match$2[1], /* [] */0) && Caml_obj.caml_equal(object_row(ty1).desc, /* Tnil */0) || Caml_obj.caml_notequal(match$2[2], /* [] */0) && Caml_obj.caml_equal(object_row(ty2).desc, /* Tnil */0)) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   Stdlib__List.iter((function (param) {
           mcomp_kind(param[1], param[3]);
@@ -32629,34 +33269,38 @@ function mcomp_kind(k1, k2) {
   var k2$1 = field_kind_repr(k2);
   if (typeof k1$1 === "number") {
     if (k1$1) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     }
     if (typeof k2$1 === "number") {
       if (!k2$1) {
         return ;
       }
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   if (typeof k2$1 === "number") {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   
 }
@@ -32666,20 +33310,22 @@ function mcomp_type_option(type_pairs, env, t, t$p) {
     if (t$p !== undefined) {
       return mcomp(type_pairs, env, t, t$p);
     }
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   if (t$p === undefined) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: Unify,
-        _1: /* [] */0,
-        Error: new Error()
-      };
+  throw new Error(Unify, {
+            cause: {
+              MEL_EXN_ID: Unify,
+              _1: /* [] */0
+            }
+          });
 }
 
 function mcomp_record_description(type_pairs, env) {
@@ -32697,26 +33343,29 @@ function mcomp_record_description(type_pairs, env) {
             _x = x.tl;
             continue ;
           }
-          throw {
-                MEL_EXN_ID: Unify,
-                _1: /* [] */0,
-                Error: new Error()
-              };
+          throw new Error(Unify, {
+                    cause: {
+                      MEL_EXN_ID: Unify,
+                      _1: /* [] */0
+                    }
+                  });
         }
-        throw {
-              MEL_EXN_ID: Unify,
-              _1: /* [] */0,
-              Error: new Error()
-            };
+        throw new Error(Unify, {
+                  cause: {
+                    MEL_EXN_ID: Unify,
+                    _1: /* [] */0
+                  }
+                });
       }
       if (!y) {
         return ;
       }
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     };
   };
   return iter;
@@ -32752,30 +33401,34 @@ function find_newtype_level(env, path) {
     if (x !== undefined) {
       return x;
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            32239,
-            12
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  32239,
+                  12
+                ]
+              }
+            });
   }
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              32240,
-              20
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    32240,
+                    20
+                  ]
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -32821,29 +33474,31 @@ function eq_package_path(env, p1, p2) {
 
 var nondep_type$p = {
   contents: (function (param, param$1, param$2) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              32262,
-              37
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    32262,
+                    37
+                  ]
+                }
+              });
     })
 };
 
 var package_subtype = {
   contents: (function (param, param$1, param$2, param$3, param$4, param$5, param$6) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              32263,
-              48
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    32263,
+                    48
+                  ]
+                }
+              });
     })
 };
 
@@ -32919,18 +33574,20 @@ function complete_type_list(allow_absentOpt, env, nl1, lv2, mty2, nl2, tl2) {
                     })(n), env$p);
           var decl = match[1];
           if (decl.type_arity !== 0) {
-            throw {
-                  MEL_EXN_ID: Stdlib.Exit,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Exit, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Exit
+                      }
+                    });
           }
           var match$1 = decl.type_kind;
           if (typeof match$1 === "number") {
             if (match$1) {
-              throw {
-                    MEL_EXN_ID: Stdlib.Exit,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Exit, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Exit
+                        }
+                      });
             }
             if (decl.type_private) {
               var t2 = decl.type_manifest;
@@ -32946,20 +33603,23 @@ function complete_type_list(allow_absentOpt, env, nl1, lv2, mty2, nl2, tl2) {
               if (allow_absent) {
                 return complete(nl, ntl2);
               }
-              throw {
-                    MEL_EXN_ID: Stdlib.Exit,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Exit, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Exit
+                        }
+                      });
             }
-            throw {
-                  MEL_EXN_ID: Stdlib.Exit,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Exit, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Exit
+                      }
+                    });
           }
-          throw {
-                MEL_EXN_ID: Stdlib.Exit,
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Exit, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Exit
+                    }
+                  });
         }
         catch (raw_exn){
           var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
@@ -32975,12 +33635,15 @@ function complete_type_list(allow_absentOpt, env, nl1, lv2, mty2, nl2, tl2) {
           }
           if (exit$1 === 2) {
             if (exn.MEL_EXN_ID === Stdlib.Exit) {
-              throw {
-                    MEL_EXN_ID: Stdlib.Not_found,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Not_found, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Not_found
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           
         }
@@ -33008,10 +33671,11 @@ function unify_package(env, unify_list, lv1, p1, n1, tl1, lv2, p2, n2, tl2) {
   if (eq_package_path(env, p1, p2) || Curry._7(package_subtype.contents, env, p1, n1, tl1, p2, n2, tl2) && Curry._7(package_subtype.contents, env, p2, n2, tl2, p1, n1, tl1)) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function unify_eq(env, t1, t2) {
@@ -33031,7 +33695,9 @@ function unify_eq(env, t1, t2) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -33102,7 +33768,9 @@ function unify(env, t1, t2) {
                           if (exn.MEL_EXN_ID === Cannot_expand) {
                             unify2(env, t1$1, t2$1);
                           } else {
-                            throw exn;
+                            throw new Error(exn.MEL_EXN_ID, {
+                                      cause: exn
+                                    });
                           }
                         }
                       } else {
@@ -33153,19 +33821,22 @@ function unify(env, t1, t2) {
     var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
     if (exn$1.MEL_EXN_ID === Unify) {
       reset_trace_gadt_instances(reset_tracing);
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: {
-              hd: [
-                t1$1,
-                t2$1
-              ],
-              tl: exn$1._1
-            },
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: {
+                    hd: [
+                      t1$1,
+                      t2$1
+                    ],
+                    tl: exn$1._1
+                  }
+                }
+              });
     }
-    throw exn$1;
+    throw new Error(exn$1.MEL_EXN_ID, {
+              cause: exn$1
+            });
   }
 }
 
@@ -33268,15 +33939,16 @@ function unify_kind(k1, k2) {
     }
     
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          32636,
-          37
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                32636,
+                37
+              ]
+            }
+          });
 }
 
 function unify3(env, t1, t1$p, t2, t2$p) {
@@ -33368,11 +34040,12 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                 exit$2 = 3;
                 break;
             default:
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: /* [] */0,
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: /* [] */0
+                        }
+                      });
           }
         }
         
@@ -33381,11 +34054,12 @@ function unify3(env, t1, t1$p, t2, t2$p) {
           case /* Tarrow */1 :
               var l1 = d1._0;
               if (typeof d2 === "number") {
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
               }
               switch (d2.TAG | 0) {
                 case /* Tarrow */1 :
@@ -33405,31 +34079,34 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                         set_commu(match$1._0, match$2);
                       }
                     } else {
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                     }
                     break;
                 case /* Tconstr */3 :
                     exit$4 = 5;
                     break;
                 default:
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
               }
               break;
           case /* Ttuple */2 :
               if (typeof d2 === "number") {
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
               }
               switch (d2.TAG | 0) {
                 case /* Ttuple */2 :
@@ -33439,11 +34116,12 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                     exit$4 = 5;
                     break;
                 default:
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
               }
               break;
           case /* Tconstr */3 :
@@ -33492,7 +34170,9 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                                   return false;
                                 }), tl1);
                         } else {
-                          throw exn;
+                          throw new Error(exn.MEL_EXN_ID, {
+                                    cause: exn
+                                  });
                         }
                       }
                       Stdlib__List.iter2((function (i, param) {
@@ -33513,7 +34193,9 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                                                   reify(env, t1);
                                                   return reify(env, t2);
                                                 }
-                                                throw exn;
+                                                throw new Error(exn.MEL_EXN_ID, {
+                                                          cause: exn
+                                                        });
                                               }
                                             }));
                               }
@@ -33579,11 +34261,12 @@ function unify3(env, t1, t1$p, t2, t2$p) {
               break;
           case /* Tobject */4 :
               if (typeof d2 === "number") {
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
               }
               switch (d2.TAG | 0) {
                 case /* Tconstr */3 :
@@ -33629,11 +34312,12 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                     }
                     break;
                 default:
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
               }
               break;
           case /* Tfield */5 :
@@ -33645,21 +34329,23 @@ function unify3(env, t1, t1$p, t2, t2$p) {
               } else if (d2.TAG === /* Tconstr */3) {
                 exit$4 = 5;
               } else {
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
               }
               break;
           case /* Tvariant */8 :
               var row1 = d1._0;
               if (typeof d2 === "number") {
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
               }
               switch (d2.TAG | 0) {
                 case /* Tconstr */3 :
@@ -33685,17 +34371,20 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                           }
                           
                         } else {
-                          throw exn$1;
+                          throw new Error(exn$1.MEL_EXN_ID, {
+                                    cause: exn$1
+                                  });
                         }
                       }
                     }
                     break;
                 default:
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
               }
               break;
           case /* Tpoly */10 :
@@ -33706,11 +34395,12 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                 exit$8 = 6;
               } else {
                 if (typeof d2 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 switch (d2.TAG | 0) {
                   case /* Tconstr */3 :
@@ -33724,20 +34414,22 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                       }
                       break;
                   default:
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                 }
               }
               if (exit$8 === 6) {
                 if (typeof d2 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 switch (d2.TAG | 0) {
                   case /* Tconstr */3 :
@@ -33749,22 +34441,24 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                             }));
                       break;
                   default:
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                 }
               }
               break;
           case /* Tpackage */11 :
               var tl1$2 = d1._2;
               if (typeof d2 === "number") {
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
               }
               switch (d2.TAG | 0) {
                 case /* Tconstr */3 :
@@ -33781,26 +34475,30 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                       var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
                       if (exn$2.MEL_EXN_ID === Stdlib.Not_found) {
                         if (umode.contents === /* Expression */0) {
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                         Stdlib__List.iter((function (param) {
                                 return reify(env, param);
                               }), Stdlib.$at(tl1$2, tl2$1));
                       } else {
-                        throw exn$2;
+                        throw new Error(exn$2.MEL_EXN_ID, {
+                                  cause: exn$2
+                                });
                       }
                     }
                     break;
                 default:
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
               }
               break;
           default:
@@ -33831,20 +34529,22 @@ function unify3(env, t1, t1$p, t2, t2$p) {
       }
       if (exit$3 === 4) {
         if (typeof d1 === "number") {
-          throw {
-                MEL_EXN_ID: Unify,
-                _1: /* [] */0,
-                Error: new Error()
-              };
+          throw new Error(Unify, {
+                    cause: {
+                      MEL_EXN_ID: Unify,
+                      _1: /* [] */0
+                    }
+                  });
         }
         if (d1.TAG === /* Tconstr */3) {
           exit$2 = 2;
         } else {
-          throw {
-                MEL_EXN_ID: Unify,
-                _1: /* [] */0,
-                Error: new Error()
-              };
+          throw new Error(Unify, {
+                    cause: {
+                      MEL_EXN_ID: Unify,
+                      _1: /* [] */0
+                    }
+                  });
         }
       }
       switch (exit$2) {
@@ -33857,21 +34557,23 @@ function unify3(env, t1, t1$p, t2, t2$p) {
               }
               
             } else {
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: /* [] */0,
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: /* [] */0
+                        }
+                      });
             }
             break;
         case 3 :
             var r = field_kind_repr(kind);
             if (typeof r === "number") {
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: /* [] */0,
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: /* [] */0
+                        }
+                      });
             }
             if (f !== dummy_method) {
               set_kind(r._0, /* Fabsent */1);
@@ -33881,11 +34583,12 @@ function unify3(env, t1, t1$p, t2, t2$p) {
                 unify(env, newty2(rem.level, /* Tnil */0), rem);
               }
             } else {
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: /* [] */0,
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: /* [] */0
+                        }
+                      });
             }
             break;
         
@@ -33912,13 +34615,16 @@ function unify3(env, t1, t1$p, t2, t2$p) {
       var exn$3 = Caml_js_exceptions.internalToOCamlException(raw_exn$3);
       if (exn$3.MEL_EXN_ID === Unify) {
         t1$p.desc = d1;
-        throw {
-              MEL_EXN_ID: Unify,
-              _1: exn$3._1,
-              Error: new Error()
-            };
+        throw new Error(Unify, {
+                  cause: {
+                    MEL_EXN_ID: Unify,
+                    _1: exn$3._1
+                  }
+                });
       }
-      throw exn$3;
+      throw new Error(exn$3.MEL_EXN_ID, {
+                cause: exn$3
+              });
     }
   }
   
@@ -33972,19 +34678,22 @@ function unify_fields(env, ty1, ty2) {
                         _2: t2,
                         _3: desc_3$1
                       };
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: {
-                              hd: [
-                                newty2(current_level.contents, desc),
-                                newty2(current_level.contents, desc$1)
-                              ],
-                              tl: exn._1
-                            },
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: {
+                                    hd: [
+                                      newty2(current_level.contents, desc),
+                                      newty2(current_level.contents, desc$1)
+                                    ],
+                                    tl: exn._1
+                                  }
+                                }
+                              });
                     }
-                    throw exn;
+                    throw new Error(exn.MEL_EXN_ID, {
+                              cause: exn
+                            });
                   }
                 }), match$2[0]);
   }
@@ -33993,17 +34702,20 @@ function unify_fields(env, ty1, ty2) {
     rest1.desc = d1;
     log_type(rest2);
     rest2.desc = d2;
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
 function unify_list(env, tl1, tl2) {
   if (Stdlib__List.length(tl1) !== Stdlib__List.length(tl2)) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   Stdlib__List.iter2((function (param, param$1) {
           return unify(env, param, param$1);
@@ -34031,19 +34743,22 @@ function unify_row(env, row1, row2) {
     Stdlib__List.iter((function (param) {
             var l = param[0];
             try {
-              throw {
-                    MEL_EXN_ID: Tags,
-                    _1: l,
-                    _2: Stdlib__Hashtbl.find(ht, hash_variant(l)),
-                    Error: new Error()
-                  };
+              throw new Error(Tags, {
+                        cause: {
+                          MEL_EXN_ID: Tags,
+                          _1: l,
+                          _2: Stdlib__Hashtbl.find(ht, hash_variant(l))
+                        }
+                      });
             }
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                 return ;
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }), r2);
   }
@@ -34079,17 +34794,18 @@ function unify_row(env, row1, row2) {
               return Caml_obj.caml_equal(row_field_repr_aux(/* [] */0, param[2]), /* Rabsent */0);
             }
           }), pairs)) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: {
-            hd: [
-              mkvariant(/* [] */0, true),
-              mkvariant(/* [] */0, true)
-            ],
-            tl: /* [] */0
-          },
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: {
+                  hd: [
+                    mkvariant(/* [] */0, true),
+                    mkvariant(/* [] */0, true)
+                  ],
+                  tl: /* [] */0
+                }
+              }
+            });
   }
   var name = row1$1.row_name !== undefined && (row1$1.row_closed || empty(r2)) && (!row2$1.row_closed || keep(function (f1, f2) {
           return [
@@ -34109,20 +34825,21 @@ function unify_row(env, row1, row2) {
     if (Caml_obj.caml_notequal(rest$1, /* [] */0) && (row.row_closed || row_fixed(row)) || closed && row_fixed(row) && !row.row_closed) {
       var t1 = mkvariant(/* [] */0, true);
       var t2 = mkvariant(rest$1, false);
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: {
-              hd: row === row1$1 ? [
-                  t1,
-                  t2
-                ] : [
-                  t2,
-                  t1
-                ],
-              tl: /* [] */0
-            },
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: {
+                    hd: row === row1$1 ? [
+                        t1,
+                        t2
+                      ] : [
+                        t2,
+                        t1
+                      ],
+                    tl: /* [] */0
+                  }
+                }
+              });
     }
     var rm = row_more(row);
     if (trace_gadt_instances.contents && Caml_obj.caml_equal(rm.desc, /* Tnil */0) || !trace_gadt_instances.contents) {
@@ -34181,61 +34898,68 @@ function unify_row(env, row1, row2) {
                           return ;
                         }
                         if (f2$2.TAG === /* Rpresent */0) {
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                         if (f2$2._2) {
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                         if (!fixed2) {
                           return set_row_field(f2$2._3, f1$2);
                         }
-                        throw {
-                              MEL_EXN_ID: Unify,
-                              _1: /* [] */0,
-                              Error: new Error()
-                            };
+                        throw new Error(Unify, {
+                                  cause: {
+                                    MEL_EXN_ID: Unify,
+                                    _1: /* [] */0
+                                  }
+                                });
                       } else if (f1$2.TAG === /* Rpresent */0) {
                         var t1 = f1$2._0;
                         if (t1 !== undefined) {
                           if (typeof f2$2 === "number") {
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           if (f2$2.TAG === /* Rpresent */0) {
                             var t2 = f2$2._0;
                             if (t2 !== undefined) {
                               return unify(env, t1, t2);
                             }
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           if (f2$2._0) {
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           if (fixed2) {
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           var e2 = f2$2._3;
                           set_row_field(e2, f1$2);
@@ -34249,48 +34973,55 @@ function unify_row(env, row1, row2) {
                           }
                           catch (exn){
                             e2.contents = undefined;
-                            throw exn;
+                            throw new Error(exn.MEL_EXN_ID, {
+                                      cause: exn
+                                    });
                           }
                         } else {
                           if (typeof f2$2 === "number") {
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           if (f2$2.TAG === /* Rpresent */0) {
                             if (f2$2._0 === undefined) {
                               return ;
                             }
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           if (f2$2._0) {
                             if (f2$2._1) {
-                              throw {
-                                    MEL_EXN_ID: Unify,
-                                    _1: /* [] */0,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Unify, {
+                                        cause: {
+                                          MEL_EXN_ID: Unify,
+                                          _1: /* [] */0
+                                        }
+                                      });
                             }
                             if (!fixed2) {
                               return set_row_field(f2$2._3, f1$2);
                             }
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                       } else {
                         var c1 = f1$2._0;
@@ -34299,54 +35030,60 @@ function unify_row(env, row1, row2) {
                         var e1 = f1$2._3;
                         if (typeof f2$2 === "number") {
                           if (m1) {
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           if (!fixed1) {
                             return set_row_field(f1$2._3, f2$2);
                           }
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                         if (f2$2.TAG === /* Rpresent */0) {
                           if (c1) {
                             if (f1$2._1) {
-                              throw {
-                                    MEL_EXN_ID: Unify,
-                                    _1: /* [] */0,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Unify, {
+                                        cause: {
+                                          MEL_EXN_ID: Unify,
+                                          _1: /* [] */0
+                                        }
+                                      });
                             }
                             if (f2$2._0 !== undefined) {
-                              throw {
-                                    MEL_EXN_ID: Unify,
-                                    _1: /* [] */0,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Unify, {
+                                        cause: {
+                                          MEL_EXN_ID: Unify,
+                                          _1: /* [] */0
+                                        }
+                                      });
                             }
                             if (!fixed1) {
                               return set_row_field(f1$2._3, f2$2);
                             }
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           var t2$1 = f2$2._0;
                           if (t2$1 !== undefined) {
                             if (fixed1) {
-                              throw {
-                                    MEL_EXN_ID: Unify,
-                                    _1: /* [] */0,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Unify, {
+                                        cause: {
+                                          MEL_EXN_ID: Unify,
+                                          _1: /* [] */0
+                                        }
+                                      });
                             }
                             var e1$1 = f1$2._3;
                             set_row_field(e1$1, f2$2);
@@ -34360,14 +35097,17 @@ function unify_row(env, row1, row2) {
                             }
                             catch (exn$1){
                               e1$1.contents = undefined;
-                              throw exn$1;
+                              throw new Error(exn$1.MEL_EXN_ID, {
+                                        cause: exn$1
+                                      });
                             }
                           } else {
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                         } else {
                           var e2$1 = f2$2._3;
@@ -34384,11 +35124,12 @@ function unify_row(env, row1, row2) {
                             if (match) {
                               var t1$1 = match.hd;
                               if (c1 || c2) {
-                                throw {
-                                      MEL_EXN_ID: Unify,
-                                      _1: /* [] */0,
-                                      Error: new Error()
-                                    };
+                                throw new Error(Unify, {
+                                          cause: {
+                                            MEL_EXN_ID: Unify,
+                                            _1: /* [] */0
+                                          }
+                                        });
                               }
                               Stdlib__List.iter((function(t1$1){
                                   return function (param) {
@@ -34465,31 +35206,34 @@ function unify_row(env, row1, row2) {
                   catch (raw_exn){
                     var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn);
                     if (exn$2.MEL_EXN_ID === Unify) {
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: {
-                              hd: [
-                                mkvariant({
-                                      hd: [
-                                        l,
-                                        f1
-                                      ],
-                                      tl: /* [] */0
-                                    }, true),
-                                mkvariant({
-                                      hd: [
-                                        l,
-                                        f2
-                                      ],
-                                      tl: /* [] */0
-                                    }, true)
-                              ],
-                              tl: exn$2._1
-                            },
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: {
+                                    hd: [
+                                      mkvariant({
+                                            hd: [
+                                              l,
+                                              f1
+                                            ],
+                                            tl: /* [] */0
+                                          }, true),
+                                      mkvariant({
+                                            hd: [
+                                              l,
+                                              f2
+                                            ],
+                                            tl: /* [] */0
+                                          }, true)
+                                    ],
+                                    tl: exn$2._1
+                                  }
+                                }
+                              });
                     }
-                    throw exn$2;
+                    throw new Error(exn$2.MEL_EXN_ID, {
+                              cause: exn$2
+                            });
                   }
                 }), pairs);
   }
@@ -34498,7 +35242,9 @@ function unify_row(env, row1, row2) {
     rm1.desc = md1;
     log_type(rm2);
     rm2.desc = md2;
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -34578,18 +35324,21 @@ function unify2(env, t1, t2) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: Stdlib__List.map((function (param) {
-                    return [
-                            param[1],
-                            param[0]
-                          ];
-                  }), exn._1),
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: Stdlib__List.map((function (param) {
+                          return [
+                                  param[1],
+                                  param[0]
+                                ];
+                        }), exn._1)
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -34600,26 +35349,30 @@ function unify$1(env, ty1, ty2) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: expand_trace(env.contents, exn._1),
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: expand_trace(env.contents, exn._1)
+                }
+              });
     }
     if (exn.MEL_EXN_ID === Recursive_abbrev) {
-      throw {
-            MEL_EXN_ID: Unification_recursive_abbrev,
-            _1: expand_trace(env.contents, {
-                  hd: [
-                    ty1,
-                    ty2
-                  ],
-                  tl: /* [] */0
-                }),
-            Error: new Error()
-          };
+      throw new Error(Unification_recursive_abbrev, {
+                cause: {
+                  MEL_EXN_ID: Unification_recursive_abbrev,
+                  _1: expand_trace(env.contents, {
+                        hd: [
+                          ty1,
+                          ty2
+                        ],
+                        tl: /* [] */0
+                      })
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -34658,13 +35411,16 @@ function unify_var(env, t1, t2) {
             ],
             tl: exn._1
           });
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: expanded_trace,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: expanded_trace
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -34692,11 +35448,12 @@ function filter_arrow(env, t, l) {
   var t$1 = expand_head_trace(env, t);
   var match = t$1.desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   switch (match.TAG | 0) {
     case /* Tvar */0 :
@@ -34729,17 +35486,19 @@ function filter_arrow(env, t, l) {
                   match._2
                 ];
         }
-        throw {
-              MEL_EXN_ID: Unify,
-              _1: /* [] */0,
-              Error: new Error()
-            };
+        throw new Error(Unify, {
+                  cause: {
+                    MEL_EXN_ID: Unify,
+                    _1: /* [] */0
+                  }
+                });
     default:
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
   }
 }
 
@@ -34749,11 +35508,12 @@ function filter_method_field(env, name, priv, _ty) {
     var ty$1 = expand_head_trace(env, ty);
     var match = ty$1.desc;
     if (typeof match === "number") {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     }
     switch (match.TAG | 0) {
       case /* Tvar */0 :
@@ -34790,11 +35550,12 @@ function filter_method_field(env, name, priv, _ty) {
           _ty = match._3;
           continue ;
       default:
-        throw {
-              MEL_EXN_ID: Unify,
-              _1: /* [] */0,
-              Error: new Error()
-            };
+        throw new Error(Unify, {
+                  cause: {
+                    MEL_EXN_ID: Unify,
+                    _1: /* [] */0
+                  }
+                });
     }
   };
 }
@@ -34803,11 +35564,12 @@ function filter_method(env, name, priv, ty) {
   var ty$1 = expand_head_trace(env, ty);
   var match = ty$1.desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   switch (match.TAG | 0) {
     case /* Tvar */0 :
@@ -34819,11 +35581,12 @@ function filter_method(env, name, priv, ty) {
     case /* Tobject */4 :
         return filter_method_field(env, name, priv, match._0);
     default:
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
   }
 }
 
@@ -34843,7 +35606,9 @@ function filter_self_method(env, lab, priv, meths, ty) {
       meths.contents = Curry._3(add$1, lab, pair, meths.contents);
       return pair;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -34854,10 +35619,11 @@ function moregen_occur(env, level, ty) {
       return ;
     }
     if (is_Tvar(ty$1) && ty$1.level >= 99999999) {
-      throw {
-            MEL_EXN_ID: Occur,
-            Error: new Error()
-          };
+      throw new Error(Occur, {
+                cause: {
+                  MEL_EXN_ID: Occur
+                }
+              });
     }
     ty$1.level = pivot_level - ty$1.level | 0;
     var row = ty$1.desc;
@@ -34882,13 +35648,16 @@ function moregen_occur(env, level, ty) {
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Occur) {
       unmark_type(ty);
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   occur_univar(env, ty);
   update_level(env, level, ty);
@@ -34968,11 +35737,12 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
             if (typeof match$3 === "number") {
               return ;
             }
-            throw {
-                  MEL_EXN_ID: Unify,
-                  _1: /* [] */0,
-                  Error: new Error()
-                };
+            throw new Error(Unify, {
+                      cause: {
+                        MEL_EXN_ID: Unify,
+                        _1: /* [] */0
+                      }
+                    });
           }
           switch (match$2.TAG | 0) {
             case /* Tvar */0 :
@@ -34980,18 +35750,20 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                   moregen_occur(env, t1$p$1.level, t2$1);
                   return link_type(t1$p$1, t2$1);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tarrow */1 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tarrow */1) {
                   var l2 = match$3._0;
@@ -35000,102 +35772,115 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                     moregen(inst_nongen, type_pairs, env, match$2._1, match$3._1);
                     return moregen(inst_nongen, type_pairs, env, match$2._2, match$3._2);
                   }
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Ttuple */2 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Ttuple */2) {
                   return moregen_list(inst_nongen, type_pairs, env, match$2._0, match$3._0);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tconstr */3 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tconstr */3) {
                   if (same(match$2._0, match$3._0)) {
                     return moregen_list(inst_nongen, type_pairs, env, match$2._1, match$3._1);
                   }
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tobject */4 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tobject */4) {
                   return moregen_fields(inst_nongen, type_pairs, env, match$2._0, match$3._0);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tfield */5 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tfield */5) {
                   return moregen_fields(inst_nongen, type_pairs, env, t1$p$1, t2$p$1);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tlink */6 :
             case /* Tsubst */7 :
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tvariant */8 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tvariant */8) {
                   var row1 = match$2._0;
@@ -35120,11 +35905,12 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                     ];
                   var r2$1 = match$5[1];
                   if (Caml_obj.caml_notequal(match$5[0], /* [] */0) || row1$1.row_closed && (!row2$1.row_closed || Caml_obj.caml_notequal(r2$1, /* [] */0))) {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   var match$6 = rm1.desc;
                   var match$7 = rm2.desc;
@@ -35134,20 +35920,22 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                     exit$2 = 2;
                   } else {
                     if (typeof match$7 === "number") {
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                     }
                     if (match$7.TAG === /* Tunivar */9) {
                       unify_univar(rm1, rm2, univar_pairs.contents);
                     } else {
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                     }
                   }
                   if (exit$2 === 2) {
@@ -35155,11 +35943,12 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                       exit$1 = 1;
                     } else {
                       if (match$7.TAG === /* Tunivar */9) {
-                        throw {
-                              MEL_EXN_ID: Unify,
-                              _1: /* [] */0,
-                              Error: new Error()
-                            };
+                        throw new Error(Unify, {
+                                  cause: {
+                                    MEL_EXN_ID: Unify,
+                                    _1: /* [] */0
+                                  }
+                                });
                       }
                       exit$1 = 1;
                     }
@@ -35181,35 +35970,39 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                       link_type(rm1, ext);
                     } else {
                       if (typeof match$6 === "number") {
-                        throw {
-                              MEL_EXN_ID: Unify,
-                              _1: /* [] */0,
-                              Error: new Error()
-                            };
+                        throw new Error(Unify, {
+                                  cause: {
+                                    MEL_EXN_ID: Unify,
+                                    _1: /* [] */0
+                                  }
+                                });
                       }
                       if (match$6.TAG === /* Tconstr */3) {
                         if (typeof match$7 === "number") {
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                         if (match$7.TAG === /* Tconstr */3) {
                           moregen(inst_nongen, type_pairs, env, rm1, rm2);
                         } else {
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                       } else {
-                        throw {
-                              MEL_EXN_ID: Unify,
-                              _1: /* [] */0,
-                              Error: new Error()
-                            };
+                        throw new Error(Unify, {
+                                  cause: {
+                                    MEL_EXN_ID: Unify,
+                                    _1: /* [] */0
+                                  }
+                                });
                       }
                     }
                   }
@@ -35223,81 +36016,90 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                                   if (typeof f2 === "number") {
                                     return ;
                                   }
-                                  throw {
-                                        MEL_EXN_ID: Unify,
-                                        _1: /* [] */0,
-                                        Error: new Error()
-                                      };
+                                  throw new Error(Unify, {
+                                            cause: {
+                                              MEL_EXN_ID: Unify,
+                                              _1: /* [] */0
+                                            }
+                                          });
                                 }
                                 if (f1.TAG === /* Rpresent */0) {
                                   var t1 = f1._0;
                                   if (t1 !== undefined) {
                                     if (typeof f2 === "number") {
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
                                     if (f2.TAG === /* Rpresent */0) {
                                       var t2 = f2._0;
                                       if (t2 !== undefined) {
                                         return moregen(inst_nongen, type_pairs, env, t1, t2);
                                       }
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
-                                    throw {
-                                          MEL_EXN_ID: Unify,
-                                          _1: /* [] */0,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Unify, {
+                                              cause: {
+                                                MEL_EXN_ID: Unify,
+                                                _1: /* [] */0
+                                              }
+                                            });
                                   } else {
                                     if (typeof f2 === "number") {
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
                                     if (f2.TAG === /* Rpresent */0) {
                                       if (f2._0 === undefined) {
                                         return ;
                                       }
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
-                                    throw {
-                                          MEL_EXN_ID: Unify,
-                                          _1: /* [] */0,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Unify, {
+                                              cause: {
+                                                MEL_EXN_ID: Unify,
+                                                _1: /* [] */0
+                                              }
+                                            });
                                   }
                                 } else {
                                   var c1 = f1._0;
                                   if (c1) {
                                     if (!f1._1 && typeof f2 !== "number" && f2.TAG === /* Rpresent */0) {
                                       if (f2._0 !== undefined) {
-                                        throw {
-                                              MEL_EXN_ID: Unify,
-                                              _1: /* [] */0,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Unify, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Unify,
+                                                    _1: /* [] */0
+                                                  }
+                                                });
                                       }
                                       if (may_inst) {
                                         return set_row_field(f1._3, f2);
                                       }
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
                                     
                                   } else if (typeof f2 !== "number" && f2.TAG === /* Rpresent */0) {
@@ -35309,17 +36111,19 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                                                       moregen(inst_nongen, type_pairs, env, t1, t2$1);
                                                     }), f1._1);
                                       }
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
-                                    throw {
-                                          MEL_EXN_ID: Unify,
-                                          _1: /* [] */0,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Unify, {
+                                              cause: {
+                                                MEL_EXN_ID: Unify,
+                                                _1: /* [] */0
+                                              }
+                                            });
                                   }
                                   var e1 = f1._3;
                                   var tl1 = f1._1;
@@ -35327,18 +36131,20 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                                     if (may_inst) {
                                       return set_row_field(e1, f2);
                                     }
-                                    throw {
-                                          MEL_EXN_ID: Unify,
-                                          _1: /* [] */0,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Unify, {
+                                              cause: {
+                                                MEL_EXN_ID: Unify,
+                                                _1: /* [] */0
+                                              }
+                                            });
                                   }
                                   if (f2.TAG === /* Rpresent */0) {
-                                    throw {
-                                          MEL_EXN_ID: Unify,
-                                          _1: /* [] */0,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Unify, {
+                                              cause: {
+                                                MEL_EXN_ID: Unify,
+                                                _1: /* [] */0
+                                              }
+                                            });
                                   }
                                   var e2 = f2._3;
                                   if (e1 === e2) {
@@ -35347,11 +36153,12 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                                   var tl2 = f2._1;
                                   var c2 = f2._0;
                                   if (c1 && !c2) {
-                                    throw {
-                                          MEL_EXN_ID: Unify,
-                                          _1: /* [] */0,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Unify, {
+                                              cause: {
+                                                MEL_EXN_ID: Unify,
+                                                _1: /* [] */0
+                                              }
+                                            });
                                   }
                                   set_row_field(e1, {
                                         TAG: /* Reither */1,
@@ -35374,35 +36181,39 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                                   if (!Caml_obj.caml_notequal(tl1, /* [] */0)) {
                                     return ;
                                   }
-                                  throw {
-                                        MEL_EXN_ID: Unify,
-                                        _1: /* [] */0,
-                                        Error: new Error()
-                                      };
+                                  throw new Error(Unify, {
+                                            cause: {
+                                              MEL_EXN_ID: Unify,
+                                              _1: /* [] */0
+                                            }
+                                          });
                                 }
                               }), match$4[2]);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tunivar */9 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tunivar */9) {
                   return unify_univar(t1$p$1, t2$p$1, univar_pairs.contents);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tpoly */10 :
                 var tl1 = match$2._1;
                 var t1$2 = match$2._0;
@@ -35411,11 +36222,12 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                   exit$3 = 2;
                 } else {
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   if (match$3.TAG === /* Tpoly */10) {
                     if (!match$3._1) {
@@ -35423,40 +36235,44 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                     }
                     exit$3 = 2;
                   } else {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                 }
                 if (exit$3 === 2) {
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   if (match$3.TAG === /* Tpoly */10) {
                     return enter_poly(env, univar_pairs, t1$2, tl1, match$3._0, match$3._1, (function (param, param$1) {
                                   return moregen(inst_nongen, type_pairs, env, param, param$1);
                                 }));
                   }
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 break;
             case /* Tpackage */11 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tpackage */11) {
                   try {
@@ -35467,25 +36283,31 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
                   catch (raw_exn$1){
                     var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
                     if (exn$1.MEL_EXN_ID === Stdlib.Not_found) {
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                     }
-                    throw exn$1;
+                    throw new Error(exn$1.MEL_EXN_ID, {
+                              cause: exn$1
+                            });
                   }
                 } else {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
             
           }
         } else {
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
       }
     }
@@ -35494,29 +36316,33 @@ function moregen(inst_nongen, type_pairs, env, t1, t2) {
   catch (raw_exn$2){
     var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
     if (exn$2.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: {
-              hd: [
-                t1$1,
-                t2$1
-              ],
-              tl: exn$2._1
-            },
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: {
+                    hd: [
+                      t1$1,
+                      t2$1
+                    ],
+                    tl: exn$2._1
+                  }
+                }
+              });
     }
-    throw exn$2;
+    throw new Error(exn$2.MEL_EXN_ID, {
+              cause: exn$2
+            });
   }
 }
 
 function moregen_list(inst_nongen, type_pairs, env, tl1, tl2) {
   if (Stdlib__List.length(tl1) !== Stdlib__List.length(tl2)) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   Stdlib__List.iter2((function (param, param$1) {
           return moregen(inst_nongen, type_pairs, env, param, param$1);
@@ -35529,11 +36355,12 @@ function moregen_fields(inst_nongen, type_pairs, env, ty1, ty2) {
   var rest2 = match$1[1];
   var match$2 = associate_fields(match[0], match$1[0]);
   if (Caml_obj.caml_notequal(match$2[1], /* [] */0)) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   moregen(inst_nongen, type_pairs, env, match[1], build_fields(repr(ty2).level)(match$2[2], rest2));
   Stdlib__List.iter((function (param) {
@@ -35549,31 +36376,34 @@ function moregen_fields(inst_nongen, type_pairs, env, ty1, ty2) {
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: Unify,
-                    _1: {
-                      hd: [
-                        newty2(current_level.contents, {
-                              TAG: /* Tfield */5,
-                              _0: n,
-                              _1: k1,
-                              _2: t1,
-                              _3: rest2
-                            }),
-                        newty2(current_level.contents, {
-                              TAG: /* Tfield */5,
-                              _0: n,
-                              _1: k2,
-                              _2: t2,
-                              _3: rest2
-                            })
-                      ],
-                      tl: exn._1
-                    },
-                    Error: new Error()
-                  };
+              throw new Error(Unify, {
+                        cause: {
+                          MEL_EXN_ID: Unify,
+                          _1: {
+                            hd: [
+                              newty2(current_level.contents, {
+                                    TAG: /* Tfield */5,
+                                    _0: n,
+                                    _1: k1,
+                                    _2: t1,
+                                    _3: rest2
+                                  }),
+                              newty2(current_level.contents, {
+                                    TAG: /* Tfield */5,
+                                    _0: n,
+                                    _1: k2,
+                                    _2: t2,
+                                    _3: rest2
+                                  })
+                            ],
+                            tl: exn._1
+                          }
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }), match$2[0]);
 }
@@ -35586,38 +36416,42 @@ function moregen_kind(k1, k2) {
   }
   if (typeof k1$1 === "number") {
     if (k1$1) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     }
     if (typeof k2$1 === "number") {
       if (!k2$1) {
         return ;
       }
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   var r = k1$1._0;
   if (typeof k2$1 !== "number") {
     return set_kind(r, k2$1);
   }
   if (k2$1) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   set_kind(r, k2$1);
 }
@@ -35644,7 +36478,9 @@ function moregeneral(env, inst_nongen, pat_sch, subj_sch) {
     if (exn.MEL_EXN_ID === Unify) {
       res = false;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   current_level.contents = old_level;
@@ -35754,7 +36590,9 @@ function matches(env, ty, ty$p) {
     if (exn.MEL_EXN_ID === Unify) {
       ok = false;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   backtrack(snap);
@@ -35815,11 +36653,12 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                 if (Stdlib__List.assq(t1$1, subst.contents) === t2$1) {
                   return ;
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
               }
               catch (raw_exn){
                 var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
@@ -35827,11 +36666,12 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                   if (Stdlib__List.exists((function (param) {
                             return param[1] === t2$1;
                           }), subst.contents)) {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   subst.contents = {
                     hd: [
@@ -35842,7 +36682,9 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                   };
                   return ;
                 }
-                throw exn;
+                throw new Error(exn.MEL_EXN_ID, {
+                          cause: exn
+                        });
               }
             }
             break;
@@ -35887,20 +36729,22 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
             if (typeof match$3 === "number") {
               return ;
             }
-            throw {
-                  MEL_EXN_ID: Unify,
-                  _1: /* [] */0,
-                  Error: new Error()
-                };
+            throw new Error(Unify, {
+                      cause: {
+                        MEL_EXN_ID: Unify,
+                        _1: /* [] */0
+                      }
+                    });
           }
           switch (match$2.TAG | 0) {
             case /* Tvar */0 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tvar */0) {
                   if (rename) {
@@ -35909,11 +36753,12 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                       if (Stdlib__List.assq(t1$p$1, subst.contents) === t2$p$1) {
                         return ;
                       }
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                     }
                     catch (raw_exn$2){
                       var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
@@ -35921,11 +36766,12 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                         if (Stdlib__List.exists((function (param) {
                                   return param[1] === t2$p$1;
                                 }), subst.contents)) {
-                          throw {
-                                MEL_EXN_ID: Unify,
-                                _1: /* [] */0,
-                                Error: new Error()
-                              };
+                          throw new Error(Unify, {
+                                    cause: {
+                                      MEL_EXN_ID: Unify,
+                                      _1: /* [] */0
+                                    }
+                                  });
                         }
                         subst.contents = {
                           hd: [
@@ -35936,29 +36782,34 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                         };
                         return ;
                       }
-                      throw exn$2;
+                      throw new Error(exn$2.MEL_EXN_ID, {
+                                cause: exn$2
+                              });
                     }
                   } else {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                 } else {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
             case /* Tarrow */1 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tarrow */1) {
                   var l2 = match$3._0;
@@ -35967,102 +36818,115 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                     eqtype(rename, type_pairs, subst, env, match$2._1, match$3._1);
                     return eqtype(rename, type_pairs, subst, env, match$2._2, match$3._2);
                   }
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Ttuple */2 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Ttuple */2) {
                   return eqtype_list(rename, type_pairs, subst, env, match$2._0, match$3._0);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tconstr */3 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tconstr */3) {
                   if (same(match$2._0, match$3._0)) {
                     return eqtype_list(rename, type_pairs, subst, env, match$2._1, match$3._1);
                   }
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tobject */4 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tobject */4) {
                   return eqtype_fields(rename, type_pairs, subst, env, match$2._0, match$3._0);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tfield */5 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tfield */5) {
                   return eqtype_fields(rename, type_pairs, subst, env, t1$p$1, t2$p$1);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tlink */6 :
             case /* Tsubst */7 :
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tvariant */8 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tvariant */8) {
                   var row1 = match$2._0;
@@ -36081,11 +36945,12 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                     var r2 = match$5[1];
                     var r1 = match$5[0];
                     if (row1$1.row_closed !== row2$2.row_closed || !row1$1.row_closed && (Caml_obj.caml_notequal(r1, /* [] */0) || Caml_obj.caml_notequal(r2, /* [] */0)) || Caml_obj.caml_notequal(filter_row_fields(false, Stdlib.$at(r1, r2)), /* [] */0)) {
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                     }
                     if (!static_row(row1$1)) {
                       eqtype(rename, type_pairs, subst, env, row1$1.row_more, row2$2.row_more);
@@ -36097,124 +36962,139 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                                     if (typeof match$1 === "number") {
                                       return ;
                                     }
-                                    throw {
-                                          MEL_EXN_ID: Unify,
-                                          _1: /* [] */0,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Unify, {
+                                              cause: {
+                                                MEL_EXN_ID: Unify,
+                                                _1: /* [] */0
+                                              }
+                                            });
                                   }
                                   if (match.TAG === /* Rpresent */0) {
                                     var t1 = match._0;
                                     if (t1 !== undefined) {
                                       if (typeof match$1 === "number") {
-                                        throw {
-                                              MEL_EXN_ID: Unify,
-                                              _1: /* [] */0,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Unify, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Unify,
+                                                    _1: /* [] */0
+                                                  }
+                                                });
                                       }
                                       if (match$1.TAG === /* Rpresent */0) {
                                         var t2 = match$1._0;
                                         if (t2 !== undefined) {
                                           return eqtype(rename, type_pairs, subst, env, t1, t2);
                                         }
-                                        throw {
-                                              MEL_EXN_ID: Unify,
-                                              _1: /* [] */0,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Unify, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Unify,
+                                                    _1: /* [] */0
+                                                  }
+                                                });
                                       }
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     } else {
                                       if (typeof match$1 === "number") {
-                                        throw {
-                                              MEL_EXN_ID: Unify,
-                                              _1: /* [] */0,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Unify, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Unify,
+                                                    _1: /* [] */0
+                                                  }
+                                                });
                                       }
                                       if (match$1.TAG === /* Rpresent */0) {
                                         if (match$1._0 === undefined) {
                                           return ;
                                         }
-                                        throw {
-                                              MEL_EXN_ID: Unify,
-                                              _1: /* [] */0,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Unify, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Unify,
+                                                    _1: /* [] */0
+                                                  }
+                                                });
                                       }
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
                                   } else if (match._0) {
                                     if (match._1) {
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
                                     if (typeof match$1 === "number") {
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
                                     if (match$1.TAG === /* Rpresent */0) {
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
                                     if (match$1._0) {
                                       if (match$1._1) {
-                                        throw {
-                                              MEL_EXN_ID: Unify,
-                                              _1: /* [] */0,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Unify, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Unify,
+                                                    _1: /* [] */0
+                                                  }
+                                                });
                                       }
                                       return ;
                                     }
-                                    throw {
-                                          MEL_EXN_ID: Unify,
-                                          _1: /* [] */0,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Unify, {
+                                              cause: {
+                                                MEL_EXN_ID: Unify,
+                                                _1: /* [] */0
+                                              }
+                                            });
                                   } else {
                                     var match$2 = match._1;
                                     if (match$2) {
                                       var tl1 = match$2.tl;
                                       var t1$1 = match$2.hd;
                                       if (typeof match$1 === "number") {
-                                        throw {
-                                              MEL_EXN_ID: Unify,
-                                              _1: /* [] */0,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Unify, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Unify,
+                                                    _1: /* [] */0
+                                                  }
+                                                });
                                       }
                                       if (match$1.TAG === /* Rpresent */0) {
-                                        throw {
-                                              MEL_EXN_ID: Unify,
-                                              _1: /* [] */0,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Unify, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Unify,
+                                                    _1: /* [] */0
+                                                  }
+                                                });
                                       }
                                       if (match$1._0) {
-                                        throw {
-                                              MEL_EXN_ID: Unify,
-                                              _1: /* [] */0,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Unify, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Unify,
+                                                    _1: /* [] */0
+                                                  }
+                                                });
                                       }
                                       var match$3 = match$1._1;
                                       if (match$3) {
@@ -36234,43 +37114,48 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                                                       }), tl1);
                                         }
                                       }
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     } else {
-                                      throw {
-                                            MEL_EXN_ID: Unify,
-                                            _1: /* [] */0,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Unify, {
+                                                cause: {
+                                                  MEL_EXN_ID: Unify,
+                                                  _1: /* [] */0
+                                                }
+                                              });
                                     }
                                   }
                                 }), match$5[2]);
                   };
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tunivar */9 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tunivar */9) {
                   return unify_univar(t1$p$1, t2$p$1, univar_pairs.contents);
                 }
-                throw {
-                      MEL_EXN_ID: Unify,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Unify, {
+                          cause: {
+                            MEL_EXN_ID: Unify,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Tpoly */10 :
                 var tl1 = match$2._1;
                 var t1$2 = match$2._0;
@@ -36279,11 +37164,12 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                   exit$1 = 2;
                 } else {
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   if (match$3.TAG === /* Tpoly */10) {
                     if (!match$3._1) {
@@ -36291,40 +37177,44 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                     }
                     exit$1 = 2;
                   } else {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                 }
                 if (exit$1 === 2) {
                   if (typeof match$3 === "number") {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: /* [] */0,
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: /* [] */0
+                              }
+                            });
                   }
                   if (match$3.TAG === /* Tpoly */10) {
                     return enter_poly(env, univar_pairs, t1$2, tl1, match$3._0, match$3._1, (function (param, param$1) {
                                   return eqtype(rename, type_pairs, subst, env, param, param$1);
                                 }));
                   }
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 break;
             case /* Tpackage */11 :
                 if (typeof match$3 === "number") {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
                 if (match$3.TAG === /* Tpackage */11) {
                   try {
@@ -36335,25 +37225,31 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
                   catch (raw_exn$3){
                     var exn$3 = Caml_js_exceptions.internalToOCamlException(raw_exn$3);
                     if (exn$3.MEL_EXN_ID === Stdlib.Not_found) {
-                      throw {
-                            MEL_EXN_ID: Unify,
-                            _1: /* [] */0,
-                            Error: new Error()
-                          };
+                      throw new Error(Unify, {
+                                cause: {
+                                  MEL_EXN_ID: Unify,
+                                  _1: /* [] */0
+                                }
+                              });
                     }
-                    throw exn$3;
+                    throw new Error(exn$3.MEL_EXN_ID, {
+                              cause: exn$3
+                            });
                   }
                 } else {
-                  throw {
-                        MEL_EXN_ID: Unify,
-                        _1: /* [] */0,
-                        Error: new Error()
-                      };
+                  throw new Error(Unify, {
+                            cause: {
+                              MEL_EXN_ID: Unify,
+                              _1: /* [] */0
+                            }
+                          });
                 }
             
           }
         } else {
-          throw exn$1;
+          throw new Error(exn$1.MEL_EXN_ID, {
+                    cause: exn$1
+                  });
         }
       }
     }
@@ -36362,29 +37258,33 @@ function eqtype(rename, type_pairs, subst, env, t1, t2) {
   catch (raw_exn$4){
     var exn$4 = Caml_js_exceptions.internalToOCamlException(raw_exn$4);
     if (exn$4.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: {
-              hd: [
-                t1$1,
-                t2$1
-              ],
-              tl: exn$4._1
-            },
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: {
+                    hd: [
+                      t1$1,
+                      t2$1
+                    ],
+                    tl: exn$4._1
+                  }
+                }
+              });
     }
-    throw exn$4;
+    throw new Error(exn$4.MEL_EXN_ID, {
+              cause: exn$4
+            });
   }
 }
 
 function eqtype_list(rename, type_pairs, subst, env, tl1, tl2) {
   if (Stdlib__List.length(tl1) !== Stdlib__List.length(tl2)) {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   Stdlib__List.iter2((function (param, param$1) {
           return eqtype(rename, type_pairs, subst, env, param, param$1);
@@ -36417,11 +37317,12 @@ function eqtype_fields(rename, type_pairs, subst, env, ty1, _ty2) {
     var match$4 = associate_fields(match[0], match$1[0]);
     eqtype(rename, type_pairs, subst, env, rest1, rest2);
     if (Caml_obj.caml_notequal(match$4[1], /* [] */0) || Caml_obj.caml_notequal(match$4[2], /* [] */0)) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     }
     return Stdlib__List.iter((function(rest2){
               return function (param) {
@@ -36437,31 +37338,34 @@ function eqtype_fields(rename, type_pairs, subst, env, ty1, _ty2) {
                 catch (raw_exn){
                   var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                   if (exn.MEL_EXN_ID === Unify) {
-                    throw {
-                          MEL_EXN_ID: Unify,
-                          _1: {
-                            hd: [
-                              newty2(current_level.contents, {
-                                    TAG: /* Tfield */5,
-                                    _0: n,
-                                    _1: k1,
-                                    _2: t1,
-                                    _3: rest2
-                                  }),
-                              newty2(current_level.contents, {
-                                    TAG: /* Tfield */5,
-                                    _0: n,
-                                    _1: k2,
-                                    _2: t2,
-                                    _3: rest2
-                                  })
-                            ],
-                            tl: exn._1
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error(Unify, {
+                              cause: {
+                                MEL_EXN_ID: Unify,
+                                _1: {
+                                  hd: [
+                                    newty2(current_level.contents, {
+                                          TAG: /* Tfield */5,
+                                          _0: n,
+                                          _1: k1,
+                                          _2: t1,
+                                          _3: rest2
+                                        }),
+                                    newty2(current_level.contents, {
+                                          TAG: /* Tfield */5,
+                                          _0: n,
+                                          _1: k2,
+                                          _2: t2,
+                                          _3: rest2
+                                        })
+                                  ],
+                                  tl: exn._1
+                                }
+                              }
+                            });
                   }
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
               }
               }(rest2)), match$4[0]);
@@ -36473,34 +37377,38 @@ function eqtype_kind(k1, k2) {
   var k2$1 = field_kind_repr(k2);
   if (typeof k1$1 === "number") {
     if (k1$1) {
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     }
     if (typeof k2$1 === "number") {
       if (!k2$1) {
         return ;
       }
-      throw {
-            MEL_EXN_ID: Unify,
-            _1: /* [] */0,
-            Error: new Error()
-          };
+      throw new Error(Unify, {
+                cause: {
+                  MEL_EXN_ID: Unify,
+                  _1: /* [] */0
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   if (typeof k2$1 === "number") {
-    throw {
-          MEL_EXN_ID: Unify,
-          _1: /* [] */0,
-          Error: new Error()
-        };
+    throw new Error(Unify, {
+              cause: {
+                MEL_EXN_ID: Unify,
+                _1: /* [] */0
+              }
+            });
   }
   
 }
@@ -36518,7 +37426,9 @@ function equal$5(env, rename, tyl1, tyl2) {
     if (exn.MEL_EXN_ID === Unify) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -36555,21 +37465,24 @@ function moregen_clty(trace, type_pairs, env, cty1, cty2) {
                         catch (raw_exn){
                           var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                           if (exn.MEL_EXN_ID === Unify) {
-                            throw {
-                                  MEL_EXN_ID: Failure,
-                                  _1: {
-                                    hd: {
-                                      TAG: /* CM_Meth_type_mismatch */5,
-                                      _0: param[0],
-                                      _1: env,
-                                      _2: expand_trace(env, exn._1)
-                                    },
-                                    tl: /* [] */0
-                                  },
-                                  Error: new Error()
-                                };
+                            throw new Error(Failure, {
+                                      cause: {
+                                        MEL_EXN_ID: Failure,
+                                        _1: {
+                                          hd: {
+                                            TAG: /* CM_Meth_type_mismatch */5,
+                                            _0: param[0],
+                                            _1: env,
+                                            _2: expand_trace(env, exn._1)
+                                          },
+                                          tl: /* [] */0
+                                        }
+                                      }
+                                    });
                           }
-                          throw exn;
+                          throw new Error(exn.MEL_EXN_ID, {
+                                    cause: exn
+                                  });
                         }
                       }), match$2[0]);
                 return Curry._2(Meths.iter, (function (lab, param) {
@@ -36580,29 +37493,33 @@ function moregen_clty(trace, type_pairs, env, cty1, cty2) {
                               catch (raw_exn){
                                 var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                                 if (exn.MEL_EXN_ID === Unify) {
-                                  throw {
-                                        MEL_EXN_ID: Failure,
-                                        _1: {
-                                          hd: {
-                                            TAG: /* CM_Val_type_mismatch */4,
-                                            _0: lab,
-                                            _1: env,
-                                            _2: expand_trace(env, exn._1)
-                                          },
-                                          tl: /* [] */0
-                                        },
-                                        Error: new Error()
-                                      };
+                                  throw new Error(Failure, {
+                                            cause: {
+                                              MEL_EXN_ID: Failure,
+                                              _1: {
+                                                hd: {
+                                                  TAG: /* CM_Val_type_mismatch */4,
+                                                  _0: lab,
+                                                  _1: env,
+                                                  _2: expand_trace(env, exn._1)
+                                                },
+                                                tl: /* [] */0
+                                              }
+                                            }
+                                          });
                                 }
-                                throw exn;
+                                throw new Error(exn.MEL_EXN_ID, {
+                                          cause: exn
+                                        });
                               }
                             }), sign2.csig_vars);
             case /* Cty_arrow */2 :
-                throw {
-                      MEL_EXN_ID: Failure,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Failure, {
+                          cause: {
+                            MEL_EXN_ID: Failure,
+                            _1: /* [] */0
+                          }
+                        });
             
           }
           break;
@@ -36612,11 +37529,12 @@ function moregen_clty(trace, type_pairs, env, cty1, cty2) {
                 exit = 1;
                 break;
             case /* Cty_signature */1 :
-                throw {
-                      MEL_EXN_ID: Failure,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Failure, {
+                          cause: {
+                            MEL_EXN_ID: Failure,
+                            _1: /* [] */0
+                          }
+                        });
             case /* Cty_arrow */2 :
                 if (cty1._0 === cty2._0) {
                   try {
@@ -36625,28 +37543,32 @@ function moregen_clty(trace, type_pairs, env, cty1, cty2) {
                   catch (raw_exn){
                     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                     if (exn.MEL_EXN_ID === Unify) {
-                      throw {
-                            MEL_EXN_ID: Failure,
-                            _1: {
-                              hd: {
-                                TAG: /* CM_Parameter_mismatch */3,
-                                _0: env,
-                                _1: expand_trace(env, exn._1)
-                              },
-                              tl: /* [] */0
-                            },
-                            Error: new Error()
-                          };
+                      throw new Error(Failure, {
+                                cause: {
+                                  MEL_EXN_ID: Failure,
+                                  _1: {
+                                    hd: {
+                                      TAG: /* CM_Parameter_mismatch */3,
+                                      _0: env,
+                                      _1: expand_trace(env, exn._1)
+                                    },
+                                    tl: /* [] */0
+                                  }
+                                }
+                              });
                     }
-                    throw exn;
+                    throw new Error(exn.MEL_EXN_ID, {
+                              cause: exn
+                            });
                   }
                   return moregen_clty(false, type_pairs, env, cty1._2, cty2._2);
                 }
-                throw {
-                      MEL_EXN_ID: Failure,
-                      _1: /* [] */0,
-                      Error: new Error()
-                    };
+                throw new Error(Failure, {
+                          cause: {
+                            MEL_EXN_ID: Failure,
+                            _1: /* [] */0
+                          }
+                        });
             
           }
           break;
@@ -36662,23 +37584,28 @@ function moregen_clty(trace, type_pairs, env, cty1, cty2) {
     if (exn$1.MEL_EXN_ID === Failure) {
       var error = exn$1._1;
       if (trace || Caml_obj.caml_equal(error, /* [] */0)) {
-        throw {
-              MEL_EXN_ID: Failure,
-              _1: {
-                hd: {
-                  TAG: /* CM_Class_type_mismatch */2,
-                  _0: env,
-                  _1: cty1,
-                  _2: cty2
-                },
-                tl: error
-              },
-              Error: new Error()
-            };
+        throw new Error(Failure, {
+                  cause: {
+                    MEL_EXN_ID: Failure,
+                    _1: {
+                      hd: {
+                        TAG: /* CM_Class_type_mismatch */2,
+                        _0: env,
+                        _1: cty1,
+                        _2: cty2
+                      },
+                      tl: error
+                    }
+                  }
+                });
       }
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
-    throw exn$1;
+    throw new Error(exn$1.MEL_EXN_ID, {
+              cause: exn$1
+            });
   }
 }
 
@@ -36752,7 +37679,9 @@ function match_class_types(traceOpt, env, pat_sch, subj_sch) {
                       tl: err
                     };
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }), match$4[0], error$1);
   var error$3 = Curry._3(Meths.fold, (function (lab, param, err) {
@@ -36789,7 +37718,9 @@ function match_class_types(traceOpt, env, pat_sch, subj_sch) {
                       tl: err
                     };
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }), sign2.csig_vars, error$2);
   var error$4 = Curry._3(Meths.fold, (function (lab, param, err) {
@@ -36840,7 +37771,9 @@ function match_class_types(traceOpt, env, pat_sch, subj_sch) {
       if (exn.MEL_EXN_ID === Failure) {
         res = exn._1;
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
   }
@@ -36887,21 +37820,24 @@ function equal_clty(trace, type_pairs, subst, env, cty1, cty2) {
                         catch (raw_exn){
                           var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                           if (exn.MEL_EXN_ID === Unify) {
-                            throw {
-                                  MEL_EXN_ID: Failure,
-                                  _1: {
-                                    hd: {
-                                      TAG: /* CM_Meth_type_mismatch */5,
-                                      _0: param[0],
-                                      _1: env,
-                                      _2: expand_trace(env, exn._1)
-                                    },
-                                    tl: /* [] */0
-                                  },
-                                  Error: new Error()
-                                };
+                            throw new Error(Failure, {
+                                      cause: {
+                                        MEL_EXN_ID: Failure,
+                                        _1: {
+                                          hd: {
+                                            TAG: /* CM_Meth_type_mismatch */5,
+                                            _0: param[0],
+                                            _1: env,
+                                            _2: expand_trace(env, exn._1)
+                                          },
+                                          tl: /* [] */0
+                                        }
+                                      }
+                                    });
                           }
-                          throw exn;
+                          throw new Error(exn.MEL_EXN_ID, {
+                                    cause: exn
+                                  });
                         }
                       }), match$2[0]);
                 return Curry._2(Meths.iter, (function (lab, param) {
@@ -36912,21 +37848,24 @@ function equal_clty(trace, type_pairs, subst, env, cty1, cty2) {
                               catch (raw_exn){
                                 var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                                 if (exn.MEL_EXN_ID === Unify) {
-                                  throw {
-                                        MEL_EXN_ID: Failure,
-                                        _1: {
-                                          hd: {
-                                            TAG: /* CM_Val_type_mismatch */4,
-                                            _0: lab,
-                                            _1: env,
-                                            _2: expand_trace(env, exn._1)
-                                          },
-                                          tl: /* [] */0
-                                        },
-                                        Error: new Error()
-                                      };
+                                  throw new Error(Failure, {
+                                            cause: {
+                                              MEL_EXN_ID: Failure,
+                                              _1: {
+                                                hd: {
+                                                  TAG: /* CM_Val_type_mismatch */4,
+                                                  _0: lab,
+                                                  _1: env,
+                                                  _2: expand_trace(env, exn._1)
+                                                },
+                                                tl: /* [] */0
+                                              }
+                                            }
+                                          });
                                 }
-                                throw exn;
+                                throw new Error(exn.MEL_EXN_ID, {
+                                          cause: exn
+                                        });
                               }
                             }), sign2.csig_vars);
             case /* Cty_arrow */2 :
@@ -36951,20 +37890,23 @@ function equal_clty(trace, type_pairs, subst, env, cty1, cty2) {
                   catch (raw_exn){
                     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                     if (exn.MEL_EXN_ID === Unify) {
-                      throw {
-                            MEL_EXN_ID: Failure,
-                            _1: {
-                              hd: {
-                                TAG: /* CM_Parameter_mismatch */3,
-                                _0: env,
-                                _1: expand_trace(env, exn._1)
-                              },
-                              tl: /* [] */0
-                            },
-                            Error: new Error()
-                          };
+                      throw new Error(Failure, {
+                                cause: {
+                                  MEL_EXN_ID: Failure,
+                                  _1: {
+                                    hd: {
+                                      TAG: /* CM_Parameter_mismatch */3,
+                                      _0: env,
+                                      _1: expand_trace(env, exn._1)
+                                    },
+                                    tl: /* [] */0
+                                  }
+                                }
+                              });
                     }
-                    throw exn;
+                    throw new Error(exn.MEL_EXN_ID, {
+                              cause: exn
+                            });
                   }
                   return equal_clty(false, type_pairs, subst, env, cty1._2, cty2._2);
                 }
@@ -36979,19 +37921,20 @@ function equal_clty(trace, type_pairs, subst, env, cty1, cty2) {
       case 1 :
           return equal_clty(true, type_pairs, subst, env, cty1, cty2._2);
       case 2 :
-          throw {
-                MEL_EXN_ID: Failure,
-                _1: trace ? /* [] */0 : ({
-                      hd: {
-                        TAG: /* CM_Class_type_mismatch */2,
-                        _0: env,
-                        _1: cty1,
-                        _2: cty2
-                      },
-                      tl: /* [] */0
-                    }),
-                Error: new Error()
-              };
+          throw new Error(Failure, {
+                    cause: {
+                      MEL_EXN_ID: Failure,
+                      _1: trace ? /* [] */0 : ({
+                            hd: {
+                              TAG: /* CM_Class_type_mismatch */2,
+                              _0: env,
+                              _1: cty1,
+                              _2: cty2
+                            },
+                            tl: /* [] */0
+                          })
+                    }
+                  });
       
     }
   }
@@ -36999,23 +37942,28 @@ function equal_clty(trace, type_pairs, subst, env, cty1, cty2) {
     var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
     if (exn$1.MEL_EXN_ID === Failure) {
       if (trace) {
-        throw {
-              MEL_EXN_ID: Failure,
-              _1: {
-                hd: {
-                  TAG: /* CM_Class_type_mismatch */2,
-                  _0: env,
-                  _1: cty1,
-                  _2: cty2
-                },
-                tl: exn$1._1
-              },
-              Error: new Error()
-            };
+        throw new Error(Failure, {
+                  cause: {
+                    MEL_EXN_ID: Failure,
+                    _1: {
+                      hd: {
+                        TAG: /* CM_Class_type_mismatch */2,
+                        _0: env,
+                        _1: cty1,
+                        _2: cty2
+                      },
+                      tl: exn$1._1
+                    }
+                  }
+                });
       }
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
-    throw exn$1;
+    throw new Error(exn$1.MEL_EXN_ID, {
+              cause: exn$1
+            });
   }
 }
 
@@ -37104,15 +38052,16 @@ function match_class_declarations(env, patt_params, patt_type, subj_params, subj
             }
             
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  33612,
-                  34
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        33612,
+                        34
+                      ]
+                    }
+                  });
         }), match$2[0], error$1);
   var error$3 = Curry._3(Meths.fold, (function (lab, param, err) {
           try {
@@ -37148,7 +38097,9 @@ function match_class_declarations(env, patt_params, patt_type, subj_params, subj
                       tl: err
                     };
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }), sign2.csig_vars, error$2);
   var error$4 = Curry._3(Meths.fold, (function (lab, param, err) {
@@ -37185,18 +38136,19 @@ function match_class_declarations(env, patt_params, patt_type, subj_params, subj
     var lp = Stdlib__List.length(patt_params);
     var ls = Stdlib__List.length(subj_params);
     if (lp !== ls) {
-      throw {
-            MEL_EXN_ID: Failure,
-            _1: {
-              hd: {
-                TAG: /* CM_Parameter_arity_mismatch */0,
-                _0: lp,
-                _1: ls
-              },
-              tl: /* [] */0
-            },
-            Error: new Error()
-          };
+      throw new Error(Failure, {
+                cause: {
+                  MEL_EXN_ID: Failure,
+                  _1: {
+                    hd: {
+                      TAG: /* CM_Parameter_arity_mismatch */0,
+                      _0: lp,
+                      _1: ls
+                    },
+                    tl: /* [] */0
+                  }
+                }
+              });
     }
     Stdlib__List.iter2((function (p, s) {
             try {
@@ -37205,20 +38157,23 @@ function match_class_declarations(env, patt_params, patt_type, subj_params, subj
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Unify) {
-                throw {
-                      MEL_EXN_ID: Failure,
-                      _1: {
-                        hd: {
-                          TAG: /* CM_Type_parameter_mismatch */1,
-                          _0: env,
-                          _1: expand_trace(env, exn._1)
-                        },
-                        tl: /* [] */0
-                      },
-                      Error: new Error()
-                    };
+                throw new Error(Failure, {
+                          cause: {
+                            MEL_EXN_ID: Failure,
+                            _1: {
+                              hd: {
+                                TAG: /* CM_Type_parameter_mismatch */1,
+                                _0: env,
+                                _1: expand_trace(env, exn._1)
+                              },
+                              tl: /* [] */0
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }), patt_params, subj_params);
     equal_clty(false, type_pairs, subst, env, {
@@ -37245,7 +38200,9 @@ function match_class_declarations(env, patt_params, patt_type, subj_params, subj
     if (exn.MEL_EXN_ID === Failure) {
       return exn._1;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -37337,10 +38294,11 @@ function find_cltype_for_path(env, p) {
   if (ty !== undefined) {
     var match$1 = repr(ty).desc;
     if (typeof match$1 === "number") {
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
     if (match$1.TAG === /* Tobject */4) {
       var match$2 = match$1._1.contents;
@@ -37351,30 +38309,34 @@ function find_cltype_for_path(env, p) {
                   ty
                 ];
         }
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
       }
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   } else {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            33719,
-            12
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  33719,
+                  12
+                ]
+              }
+            });
   }
 }
 
@@ -37419,7 +38381,9 @@ function build_subtype(env, visited, loops, posi, level, t) {
                     /* Unchanged */0
                   ];
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Tarrow */1 :
         if (memq_warn(t$1, visited)) {
@@ -37491,10 +38455,11 @@ function build_subtype(env, visited, loops, posi, level, t) {
           try {
             var match$2 = t$p$1.desc;
             if (typeof match$2 === "number") {
-              throw {
-                    MEL_EXN_ID: Stdlib.Not_found,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Not_found, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Not_found
+                        }
+                      });
             }
             if (match$2.TAG === /* Tobject */4) {
               if (posi && !opened_object(t$p$1)) {
@@ -37504,10 +38469,11 @@ function build_subtype(env, visited, loops, posi, level, t) {
                 var match$4 = ty$1.desc;
                 var match$5;
                 if (typeof match$4 === "number") {
-                  throw {
-                        MEL_EXN_ID: Stdlib.Not_found,
-                        Error: new Error()
-                      };
+                  throw new Error(Stdlib.Not_found, {
+                            cause: {
+                              MEL_EXN_ID: Stdlib.Not_found
+                            }
+                          });
                 }
                 if (match$4.TAG === /* Tobject */4) {
                   var match$6 = match$4._1.contents;
@@ -37518,31 +38484,35 @@ function build_subtype(env, visited, loops, posi, level, t) {
                         match$6[1]
                       ];
                     } else {
-                      throw {
-                            MEL_EXN_ID: Stdlib.Not_found,
-                            Error: new Error()
-                          };
+                      throw new Error(Stdlib.Not_found, {
+                                cause: {
+                                  MEL_EXN_ID: Stdlib.Not_found
+                                }
+                              });
                     }
                   } else {
-                    throw {
-                          MEL_EXN_ID: Stdlib.Not_found,
-                          Error: new Error()
-                        };
+                    throw new Error(Stdlib.Not_found, {
+                              cause: {
+                                MEL_EXN_ID: Stdlib.Not_found
+                              }
+                            });
                   }
                 } else {
-                  throw {
-                        MEL_EXN_ID: Stdlib.Not_found,
-                        Error: new Error()
-                      };
+                  throw new Error(Stdlib.Not_found, {
+                            cause: {
+                              MEL_EXN_ID: Stdlib.Not_found
+                            }
+                          });
                 }
                 var tl1 = match$5[1];
                 if (Stdlib__List.exists((function (param) {
                           return deep_occur(ty$1, param);
                         }), tl1)) {
-                  throw {
-                        MEL_EXN_ID: Stdlib.Not_found,
-                        Error: new Error()
-                      };
+                  throw new Error(Stdlib.Not_found, {
+                            cause: {
+                              MEL_EXN_ID: Stdlib.Not_found
+                            }
+                          });
                 }
                 ty$1.desc = {
                   TAG: /* Tvar */0,
@@ -37563,15 +38533,16 @@ function build_subtype(env, visited, loops, posi, level, t) {
                     }, loops$1, posi, pred_enlarge(level$p), match$5[0]);
                 var ty1$p = match$7[0];
                 if (!is_Tvar(t$p$p)) {
-                  throw {
-                        MEL_EXN_ID: "Assert_failure",
-                        _1: [
-                          "jscomp/test/ocaml_typedtree_test.ml",
-                          33782,
-                          10
-                        ],
-                        Error: new Error()
-                      };
+                  throw new Error("Assert_failure", {
+                            cause: {
+                              MEL_EXN_ID: "Assert_failure",
+                              _1: [
+                                "jscomp/test/ocaml_typedtree_test.ml",
+                                33782,
+                                10
+                              ]
+                            }
+                          });
                 }
                 var nm = match$7[1] > /* Equiv */1 || deep_occur(ty$1, ty1$p) ? undefined : [
                     p,
@@ -37590,32 +38561,37 @@ function build_subtype(env, visited, loops, posi, level, t) {
                 catch (raw_exn$1){
                   var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
                   if (exn$1.MEL_EXN_ID === Unify) {
-                    throw {
-                          MEL_EXN_ID: "Assert_failure",
-                          _1: [
-                            "jscomp/test/ocaml_typedtree_test.ml",
-                            33786,
-                            50
-                          ],
-                          Error: new Error()
-                        };
+                    throw new Error("Assert_failure", {
+                              cause: {
+                                MEL_EXN_ID: "Assert_failure",
+                                _1: [
+                                  "jscomp/test/ocaml_typedtree_test.ml",
+                                  33786,
+                                  50
+                                ]
+                              }
+                            });
                   }
-                  throw exn$1;
+                  throw new Error(exn$1.MEL_EXN_ID, {
+                            cause: exn$1
+                          });
                 }
                 return [
                         t$p$p,
                         /* Changed */2
                       ];
               }
-              throw {
-                    MEL_EXN_ID: Stdlib.Not_found,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Not_found, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Not_found
+                        }
+                      });
             }
-            throw {
-                  MEL_EXN_ID: Stdlib.Not_found,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Not_found, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Not_found
+                      }
+                    });
           }
           catch (raw_exn$2){
             var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
@@ -37634,7 +38610,9 @@ function build_subtype(env, visited, loops, posi, level, t) {
                       ];
               }
             }
-            throw exn$2;
+            throw new Error(exn$2.MEL_EXN_ID, {
+                      cause: exn$2
+                    });
           }
         } else {
           if (memq_warn(t$1, visited)) {
@@ -37696,7 +38674,9 @@ function build_subtype(env, visited, loops, posi, level, t) {
                       /* Unchanged */0
                     ];
             }
-            throw exn$3;
+            throw new Error(exn$3.MEL_EXN_ID, {
+                      cause: exn$3
+                    });
           }
         }
     case /* Tobject */4 :
@@ -37755,15 +38735,16 @@ function build_subtype(env, visited, loops, posi, level, t) {
         }
     case /* Tlink */6 :
     case /* Tsubst */7 :
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                33877,
-                6
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      33877,
+                      6
+                    ]
+                  }
+                });
     case /* Tvariant */8 :
         var row = row_repr_aux(/* [] */0, tlist._0);
         if (memq_warn(t$1, visited) || !static_row(row)) {
@@ -37783,15 +38764,16 @@ function build_subtype(env, visited, loops, posi, level, t) {
                 var l = orig[0];
                 var match = row_field_repr_aux(/* [] */0, orig[1]);
                 if (typeof match === "number") {
-                  throw {
-                        MEL_EXN_ID: "Assert_failure",
-                        _1: [
-                          "jscomp/test/ocaml_typedtree_test.ml",
-                          33844,
-                          17
-                        ],
-                        Error: new Error()
-                      };
+                  throw new Error("Assert_failure", {
+                            cause: {
+                              MEL_EXN_ID: "Assert_failure",
+                              _1: [
+                                "jscomp/test/ocaml_typedtree_test.ml",
+                                33844,
+                                17
+                              ]
+                            }
+                          });
                 }
                 if (match.TAG === /* Rpresent */0) {
                   var t = match._0;
@@ -37844,15 +38826,16 @@ function build_subtype(env, visited, loops, posi, level, t) {
                           match$1[1]
                         ];
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        33844,
-                        17
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              33844,
+                              17
+                            ]
+                          }
+                        });
               }), fields);
         var c$6 = collect(fields$1);
         var row_row_fields = Stdlib__List.map((function (prim) {
@@ -37915,12 +38898,13 @@ function enlarge_type(env, ty) {
 var subtypes = Curry._1(TypePairs.create, 17);
 
 function subtype_error(env, trace) {
-  throw {
-        MEL_EXN_ID: Subtype,
-        _1: expand_trace(env, Stdlib__List.rev(trace)),
-        _2: /* [] */0,
-        Error: new Error()
-      };
+  throw new Error(Subtype, {
+            cause: {
+              MEL_EXN_ID: Subtype,
+              _1: expand_trace(env, Stdlib__List.rev(trace)),
+              _2: /* [] */0
+            }
+          });
 }
 
 function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
@@ -38192,10 +39176,11 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                   break;
                               case /* Tunivar */9 :
                                   if (typeof match$7 === "number") {
-                                    throw {
-                                          MEL_EXN_ID: Stdlib.Exit,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Stdlib.Exit, {
+                                              cause: {
+                                                MEL_EXN_ID: Stdlib.Exit
+                                              }
+                                            });
                                   }
                                   if (match$7.TAG === /* Tunivar */9) {
                                     if (row1$1.row_closed === row2$1.row_closed && Caml_obj.caml_equal(r1, /* [] */0) && Caml_obj.caml_equal(match$5[1], /* [] */0)) {
@@ -38216,19 +39201,21 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                                     if (typeof match$1 === "number") {
                                                       return cstrs;
                                                     }
-                                                    throw {
-                                                          MEL_EXN_ID: Stdlib.Exit,
-                                                          Error: new Error()
-                                                        };
+                                                    throw new Error(Stdlib.Exit, {
+                                                              cause: {
+                                                                MEL_EXN_ID: Stdlib.Exit
+                                                              }
+                                                            });
                                                   }
                                                   if (match.TAG === /* Rpresent */0) {
                                                     var t1$1 = match._0;
                                                     if (t1$1 !== undefined) {
                                                       if (typeof match$1 === "number") {
-                                                        throw {
-                                                              MEL_EXN_ID: Stdlib.Exit,
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error(Stdlib.Exit, {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: Stdlib.Exit
+                                                                  }
+                                                                });
                                                       }
                                                       if (match$1.TAG === /* Rpresent */0) {
                                                         var t2$1 = match$1._0;
@@ -38236,118 +39223,135 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                                           t1 = t1$1;
                                                           t2 = t2$1;
                                                         } else {
-                                                          throw {
-                                                                MEL_EXN_ID: Stdlib.Exit,
-                                                                Error: new Error()
-                                                              };
+                                                          throw new Error(Stdlib.Exit, {
+                                                                    cause: {
+                                                                      MEL_EXN_ID: Stdlib.Exit
+                                                                    }
+                                                                  });
                                                         }
                                                       } else {
-                                                        throw {
-                                                              MEL_EXN_ID: Stdlib.Exit,
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error(Stdlib.Exit, {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: Stdlib.Exit
+                                                                  }
+                                                                });
                                                       }
                                                     } else {
                                                       if (typeof match$1 === "number") {
-                                                        throw {
-                                                              MEL_EXN_ID: Stdlib.Exit,
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error(Stdlib.Exit, {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: Stdlib.Exit
+                                                                  }
+                                                                });
                                                       }
                                                       if (match$1.TAG === /* Rpresent */0) {
                                                         if (match$1._0 !== undefined) {
-                                                          throw {
-                                                                MEL_EXN_ID: Stdlib.Exit,
-                                                                Error: new Error()
-                                                              };
+                                                          throw new Error(Stdlib.Exit, {
+                                                                    cause: {
+                                                                      MEL_EXN_ID: Stdlib.Exit
+                                                                    }
+                                                                  });
                                                         }
                                                         return cstrs;
                                                       }
-                                                      throw {
-                                                            MEL_EXN_ID: Stdlib.Exit,
-                                                            Error: new Error()
-                                                          };
+                                                      throw new Error(Stdlib.Exit, {
+                                                                cause: {
+                                                                  MEL_EXN_ID: Stdlib.Exit
+                                                                }
+                                                              });
                                                     }
                                                   } else if (match._0) {
                                                     if (match._1) {
-                                                      throw {
-                                                            MEL_EXN_ID: Stdlib.Exit,
-                                                            Error: new Error()
-                                                          };
+                                                      throw new Error(Stdlib.Exit, {
+                                                                cause: {
+                                                                  MEL_EXN_ID: Stdlib.Exit
+                                                                }
+                                                              });
                                                     }
                                                     if (typeof match$1 === "number") {
-                                                      throw {
-                                                            MEL_EXN_ID: Stdlib.Exit,
-                                                            Error: new Error()
-                                                          };
+                                                      throw new Error(Stdlib.Exit, {
+                                                                cause: {
+                                                                  MEL_EXN_ID: Stdlib.Exit
+                                                                }
+                                                              });
                                                     }
                                                     if (match$1.TAG === /* Rpresent */0) {
-                                                      throw {
-                                                            MEL_EXN_ID: Stdlib.Exit,
-                                                            Error: new Error()
-                                                          };
+                                                      throw new Error(Stdlib.Exit, {
+                                                                cause: {
+                                                                  MEL_EXN_ID: Stdlib.Exit
+                                                                }
+                                                              });
                                                     }
                                                     if (match$1._0) {
                                                       if (match$1._1) {
-                                                        throw {
-                                                              MEL_EXN_ID: Stdlib.Exit,
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error(Stdlib.Exit, {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: Stdlib.Exit
+                                                                  }
+                                                                });
                                                       }
                                                       return cstrs;
                                                     }
-                                                    throw {
-                                                          MEL_EXN_ID: Stdlib.Exit,
-                                                          Error: new Error()
-                                                        };
+                                                    throw new Error(Stdlib.Exit, {
+                                                              cause: {
+                                                                MEL_EXN_ID: Stdlib.Exit
+                                                              }
+                                                            });
                                                   } else {
                                                     var match$2 = match._1;
                                                     if (match$2) {
                                                       if (match$2.tl) {
-                                                        throw {
-                                                              MEL_EXN_ID: Stdlib.Exit,
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error(Stdlib.Exit, {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: Stdlib.Exit
+                                                                  }
+                                                                });
                                                       }
                                                       if (typeof match$1 === "number") {
-                                                        throw {
-                                                              MEL_EXN_ID: Stdlib.Exit,
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error(Stdlib.Exit, {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: Stdlib.Exit
+                                                                  }
+                                                                });
                                                       }
                                                       if (match$1.TAG === /* Rpresent */0) {
-                                                        throw {
-                                                              MEL_EXN_ID: Stdlib.Exit,
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error(Stdlib.Exit, {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: Stdlib.Exit
+                                                                  }
+                                                                });
                                                       }
                                                       if (match$1._0) {
-                                                        throw {
-                                                              MEL_EXN_ID: Stdlib.Exit,
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error(Stdlib.Exit, {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: Stdlib.Exit
+                                                                  }
+                                                                });
                                                       }
                                                       var match$3 = match$1._1;
                                                       if (match$3) {
                                                         if (match$3.tl) {
-                                                          throw {
-                                                                MEL_EXN_ID: Stdlib.Exit,
-                                                                Error: new Error()
-                                                              };
+                                                          throw new Error(Stdlib.Exit, {
+                                                                    cause: {
+                                                                      MEL_EXN_ID: Stdlib.Exit
+                                                                    }
+                                                                  });
                                                         }
                                                         t1 = match$2.hd;
                                                         t2 = match$3.hd;
                                                       } else {
-                                                        throw {
-                                                              MEL_EXN_ID: Stdlib.Exit,
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error(Stdlib.Exit, {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: Stdlib.Exit
+                                                                  }
+                                                                });
                                                       }
                                                     } else {
-                                                      throw {
-                                                            MEL_EXN_ID: Stdlib.Exit,
-                                                            Error: new Error()
-                                                          };
+                                                      throw new Error(Stdlib.Exit, {
+                                                                cause: {
+                                                                  MEL_EXN_ID: Stdlib.Exit
+                                                                }
+                                                              });
                                                     }
                                                   }
                                                   return subtype_rec(env, {
@@ -38360,20 +39364,23 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                                 }
                                                 }(trace)), cstrs$4, pairs);
                                     }
-                                    throw {
-                                          MEL_EXN_ID: Stdlib.Exit,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Stdlib.Exit, {
+                                              cause: {
+                                                MEL_EXN_ID: Stdlib.Exit
+                                              }
+                                            });
                                   }
-                                  throw {
-                                        MEL_EXN_ID: Stdlib.Exit,
-                                        Error: new Error()
-                                      };
+                                  throw new Error(Stdlib.Exit, {
+                                            cause: {
+                                              MEL_EXN_ID: Stdlib.Exit
+                                            }
+                                          });
                               default:
-                                throw {
-                                      MEL_EXN_ID: Stdlib.Exit,
-                                      Error: new Error()
-                                    };
+                                throw new Error(Stdlib.Exit, {
+                                          cause: {
+                                            MEL_EXN_ID: Stdlib.Exit
+                                          }
+                                        });
                             }
                           }
                           if (exit$5 === 1) {
@@ -38387,10 +39394,11 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                     exit$6 = 2;
                                     break;
                                 default:
-                                  throw {
-                                        MEL_EXN_ID: Stdlib.Exit,
-                                        Error: new Error()
-                                      };
+                                  throw new Error(Stdlib.Exit, {
+                                            cause: {
+                                              MEL_EXN_ID: Stdlib.Exit
+                                            }
+                                          });
                               }
                             }
                             if (exit$6 === 2) {
@@ -38406,10 +39414,11 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                               var t1 = match._0;
                                               if (t1 !== undefined) {
                                                 if (typeof match$1 === "number") {
-                                                  throw {
-                                                        MEL_EXN_ID: Stdlib.Exit,
-                                                        Error: new Error()
-                                                      };
+                                                  throw new Error(Stdlib.Exit, {
+                                                            cause: {
+                                                              MEL_EXN_ID: Stdlib.Exit
+                                                            }
+                                                          });
                                                 }
                                                 if (match$1.TAG === /* Rpresent */0) {
                                                   var t2 = match$1._0;
@@ -38422,15 +39431,17 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                                                 tl: trace
                                                               }, t1, t2, cstrs);
                                                   }
-                                                  throw {
-                                                        MEL_EXN_ID: Stdlib.Exit,
-                                                        Error: new Error()
-                                                      };
+                                                  throw new Error(Stdlib.Exit, {
+                                                            cause: {
+                                                              MEL_EXN_ID: Stdlib.Exit
+                                                            }
+                                                          });
                                                 }
-                                                throw {
-                                                      MEL_EXN_ID: Stdlib.Exit,
-                                                      Error: new Error()
-                                                    };
+                                                throw new Error(Stdlib.Exit, {
+                                                          cause: {
+                                                            MEL_EXN_ID: Stdlib.Exit
+                                                          }
+                                                        });
                                               }
                                               
                                             } else if (!match._0) {
@@ -38438,10 +39449,11 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                               if (match$2) {
                                                 var t1$1 = match$2.hd;
                                                 if (typeof match$1 === "number") {
-                                                  throw {
-                                                        MEL_EXN_ID: Stdlib.Exit,
-                                                        Error: new Error()
-                                                      };
+                                                  throw new Error(Stdlib.Exit, {
+                                                            cause: {
+                                                              MEL_EXN_ID: Stdlib.Exit
+                                                            }
+                                                          });
                                                 }
                                                 if (match$1.TAG === /* Rpresent */0) {
                                                   var t2$1 = match$1._0;
@@ -38454,48 +39466,55 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                                                 tl: trace
                                                               }, t1$1, t2$1, cstrs);
                                                   }
-                                                  throw {
-                                                        MEL_EXN_ID: Stdlib.Exit,
-                                                        Error: new Error()
-                                                      };
+                                                  throw new Error(Stdlib.Exit, {
+                                                            cause: {
+                                                              MEL_EXN_ID: Stdlib.Exit
+                                                            }
+                                                          });
                                                 }
-                                                throw {
-                                                      MEL_EXN_ID: Stdlib.Exit,
-                                                      Error: new Error()
-                                                    };
+                                                throw new Error(Stdlib.Exit, {
+                                                          cause: {
+                                                            MEL_EXN_ID: Stdlib.Exit
+                                                          }
+                                                        });
                                               } else {
-                                                throw {
-                                                      MEL_EXN_ID: Stdlib.Exit,
-                                                      Error: new Error()
-                                                    };
+                                                throw new Error(Stdlib.Exit, {
+                                                          cause: {
+                                                            MEL_EXN_ID: Stdlib.Exit
+                                                          }
+                                                        });
                                               }
                                             }
                                             if (typeof match$1 === "number") {
-                                              throw {
-                                                    MEL_EXN_ID: Stdlib.Exit,
-                                                    Error: new Error()
-                                                  };
+                                              throw new Error(Stdlib.Exit, {
+                                                        cause: {
+                                                          MEL_EXN_ID: Stdlib.Exit
+                                                        }
+                                                      });
                                             }
                                             if (match$1.TAG === /* Rpresent */0) {
                                               if (match$1._0 !== undefined) {
-                                                throw {
-                                                      MEL_EXN_ID: Stdlib.Exit,
-                                                      Error: new Error()
-                                                    };
+                                                throw new Error(Stdlib.Exit, {
+                                                          cause: {
+                                                            MEL_EXN_ID: Stdlib.Exit
+                                                          }
+                                                        });
                                               }
                                               return cstrs;
                                             }
-                                            throw {
-                                                  MEL_EXN_ID: Stdlib.Exit,
-                                                  Error: new Error()
-                                                };
+                                            throw new Error(Stdlib.Exit, {
+                                                      cause: {
+                                                        MEL_EXN_ID: Stdlib.Exit
+                                                      }
+                                                    });
                                           }
                                           }(trace)), cstrs, pairs);
                               }
-                              throw {
-                                    MEL_EXN_ID: Stdlib.Exit,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Stdlib.Exit, {
+                                        cause: {
+                                          MEL_EXN_ID: Stdlib.Exit
+                                        }
+                                      });
                             }
                             
                           }
@@ -38514,7 +39533,9 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                     tl: cstrs
                                   };
                           }
-                          throw exn$1;
+                          throw new Error(exn$1.MEL_EXN_ID, {
+                                    cause: exn$1
+                                  });
                         }
                     default:
                       exit = 1;
@@ -38584,7 +39605,9 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                         tl: cstrs
                                       };
                               }
-                              throw exn$2;
+                              throw new Error(exn$2.MEL_EXN_ID, {
+                                        cause: exn$2
+                                      });
                             }
                           } else {
                             var match$8 = instance_poly(undefined, false, tl1$1, u1$1);
@@ -38647,22 +39670,26 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                               backtrack(snap);
                               return Stdlib.$at(cstrs$p, cstrs);
                             }
-                            throw {
-                                  MEL_EXN_ID: Unify,
-                                  _1: /* [] */0,
-                                  Error: new Error()
-                                };
+                            throw new Error(Unify, {
+                                      cause: {
+                                        MEL_EXN_ID: Unify,
+                                        _1: /* [] */0
+                                      }
+                                    });
                           }
                           catch (raw_exn$3){
                             var exn$3 = Caml_js_exceptions.internalToOCamlException(raw_exn$3);
                             if (exn$3.MEL_EXN_ID === Unify) {
                               backtrack(snap);
-                              throw {
-                                    MEL_EXN_ID: Stdlib.Not_found,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Stdlib.Not_found, {
+                                        cause: {
+                                          MEL_EXN_ID: Stdlib.Not_found
+                                        }
+                                      });
                             }
-                            throw exn$3;
+                            throw new Error(exn$3.MEL_EXN_ID, {
+                                      cause: exn$3
+                                    });
                           }
                         }
                         catch (raw_exn$4){
@@ -38678,7 +39705,9 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                                     tl: cstrs
                                   };
                           }
-                          throw exn$4;
+                          throw new Error(exn$4.MEL_EXN_ID, {
+                                    cause: exn$4
+                                  });
                         }
                     default:
                       exit = 1;
@@ -38796,7 +39825,9 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
                           tl: cstrs
                         };
                 }
-                throw exn$5;
+                throw new Error(exn$5.MEL_EXN_ID, {
+                          cause: exn$5
+                        });
               }
             }
             if (exit$8 === 4) {
@@ -38825,7 +39856,9 @@ function subtype_rec(env, _trace, _t1, _t2, _cstrs) {
           
         }
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
   };
@@ -38852,14 +39885,17 @@ function subtype(env, ty1, ty2) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Unify) {
-                throw {
-                      MEL_EXN_ID: Subtype,
-                      _1: expand_trace(env, Stdlib__List.rev(param[0])),
-                      _2: Stdlib__List.tl(Stdlib__List.tl(exn._1)),
-                      Error: new Error()
-                    };
+                throw new Error(Subtype, {
+                          cause: {
+                            MEL_EXN_ID: Subtype,
+                            _1: expand_trace(env, Stdlib__List.rev(param[0])),
+                            _2: Stdlib__List.tl(Stdlib__List.tl(exn._1))
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }), Stdlib__List.rev(cstrs));
   };
@@ -38890,15 +39926,16 @@ function unalias_object(ty) {
     case /* Tunivar */9 :
         return ty$1;
     default:
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              34141,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    34141,
+                    6
+                  ]
+                }
+              });
   }
 }
 
@@ -38980,7 +40017,9 @@ function cyclic_abbrev(env, id, ty) {
       if (exn.MEL_EXN_ID === Unify) {
         return true;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   return check_cycle(/* [] */0, ty);
@@ -39199,18 +40238,22 @@ function nondep_type_rec(env, id, _ty) {
                     catch (raw_exn$1){
                       var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
                       if (exn$1.MEL_EXN_ID === Cannot_expand) {
-                        throw {
-                              MEL_EXN_ID: Stdlib.Not_found,
-                              Error: new Error()
-                            };
+                        throw new Error(Stdlib.Not_found, {
+                                  cause: {
+                                    MEL_EXN_ID: Stdlib.Not_found
+                                  }
+                                });
                       }
                       if (exn$1.MEL_EXN_ID === Unify) {
-                        throw {
-                              MEL_EXN_ID: Stdlib.Not_found,
-                              Error: new Error()
-                            };
+                        throw new Error(Stdlib.Not_found, {
+                                  cause: {
+                                    MEL_EXN_ID: Stdlib.Not_found
+                                  }
+                                });
                       }
-                      throw exn$1;
+                      throw new Error(exn$1.MEL_EXN_ID, {
+                                cause: exn$1
+                              });
                     }
                   } else {
                     tmp = {
@@ -39283,7 +40326,9 @@ function nondep_type_rec(env, id, _ty) {
                             _0: row$2
                           });
                     } else {
-                      throw exn$2;
+                      throw new Error(exn$2.MEL_EXN_ID, {
+                                cause: exn$2
+                              });
                     }
                   }
                   break;
@@ -39292,10 +40337,11 @@ function nondep_type_rec(env, id, _ty) {
                   if (isfree(id, p$2)) {
                     var p$p = normalize_package_path(env, p$2);
                     if (isfree(id, p$p)) {
-                      throw {
-                            MEL_EXN_ID: Stdlib.Not_found,
-                            Error: new Error()
-                          };
+                      throw new Error(Stdlib.Not_found, {
+                                cause: {
+                                  MEL_EXN_ID: Stdlib.Not_found
+                                }
+                              });
                     }
                     tmp = {
                       TAG: /* Tpackage */11,
@@ -39321,7 +40367,9 @@ function nondep_type_rec(env, id, _ty) {
           ty$p.desc = tmp;
           return ty$p;
         }
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
     
@@ -39340,12 +40388,15 @@ function nondep_type(env, id, ty) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       Curry._1(TypeHash.clear, nondep_hash);
       Curry._1(TypeHash.clear, nondep_variants);
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -39421,10 +40472,14 @@ function nondep_type_decl(env, mid, id, is_covariant, decl) {
         if (is_covariant) {
           tk = /* Type_abstract */0;
         } else {
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
     var tm;
@@ -39438,10 +40493,14 @@ function nondep_type_decl(env, mid, id, is_covariant, decl) {
         if (is_covariant) {
           tm = undefined;
         } else {
-          throw exn$1;
+          throw new Error(exn$1.MEL_EXN_ID, {
+                    cause: exn$1
+                  });
         }
       } else {
-        throw exn$1;
+        throw new Error(exn$1.MEL_EXN_ID, {
+                  cause: exn$1
+                });
       }
     }
     Curry._1(TypeHash.clear, nondep_hash);
@@ -39464,12 +40523,15 @@ function nondep_type_decl(env, mid, id, is_covariant, decl) {
     if (exn$2.MEL_EXN_ID === Stdlib.Not_found) {
       Curry._1(TypeHash.clear, nondep_hash);
       Curry._1(TypeHash.clear, nondep_variants);
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
-    throw exn$2;
+    throw new Error(exn$2.MEL_EXN_ID, {
+              cause: exn$2
+            });
   }
 }
 
@@ -39488,10 +40550,11 @@ function nondep_extension_constructor(env, mid, ext) {
       var ty$p = nondep_type_rec(env, mid, ty);
       var match$1 = repr(ty$p).desc;
       if (typeof match$1 === "number") {
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
       }
       if (match$1.TAG === /* Tconstr */3) {
         match = [
@@ -39499,10 +40562,11 @@ function nondep_extension_constructor(env, mid, ext) {
           match$1._1
         ];
       } else {
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
       }
     } else {
       var type_params = Stdlib__List.map((function (param) {
@@ -39536,12 +40600,15 @@ function nondep_extension_constructor(env, mid, ext) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       Curry._1(TypeHash.clear, nondep_hash);
       Curry._1(TypeHash.clear, nondep_variants);
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -39604,15 +40671,16 @@ function nondep_class_type(env, id, _param) {
 
 function nondep_class_declaration(env, id, decl) {
   if (isfree(id, decl.cty_path)) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            34461,
-            2
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  34461,
+                  2
+                ]
+              }
+            });
   }
   var ty = decl.cty_new;
   var decl$1 = {
@@ -39633,15 +40701,16 @@ function nondep_class_declaration(env, id, decl) {
 
 function nondep_cltype_declaration(env, id, decl) {
   if (isfree(id, decl.clty_path)) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            34480,
-            2
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  34480,
+                  2
+                ]
+              }
+            });
   }
   var decl_clty_params = Stdlib__List.map((function (param) {
           return nondep_type_rec(env, id, param);
@@ -40156,10 +41225,11 @@ function print_simple_out_type(ppf, ty) {
                                     var single = tys.hd;
                                     if (typeof single !== "number" && single.TAG === /* Otyp_tuple */9) {
                                       if (tys.tl) {
-                                        throw {
-                                              MEL_EXN_ID: Stdlib.Not_found,
-                                              Error: new Error()
-                                            };
+                                        throw new Error(Stdlib.Not_found, {
+                                                  cause: {
+                                                    MEL_EXN_ID: Stdlib.Not_found
+                                                  }
+                                                });
                                       }
                                       if (variant === "Arity_1") {
                                         return {
@@ -40180,10 +41250,11 @@ function print_simple_out_type(ppf, ty) {
                                       }
                                     }
                                     if (tys.tl) {
-                                      throw {
-                                            MEL_EXN_ID: Stdlib.Not_found,
-                                            Error: new Error()
-                                          };
+                                      throw new Error(Stdlib.Not_found, {
+                                                cause: {
+                                                  MEL_EXN_ID: Stdlib.Not_found
+                                                }
+                                              });
                                     }
                                     return {
                                             TAG: /* Otyp_arrow */1,
@@ -40192,10 +41263,11 @@ function print_simple_out_type(ppf, ty) {
                                             _2: result
                                           };
                                   }
-                                  throw {
-                                        MEL_EXN_ID: Stdlib.Not_found,
-                                        Error: new Error()
-                                      };
+                                  throw new Error(Stdlib.Not_found, {
+                                            cause: {
+                                              MEL_EXN_ID: Stdlib.Not_found
+                                            }
+                                          });
                                 };
                                 var exit$3 = 0;
                                 var res;
@@ -40317,10 +41389,11 @@ function print_simple_out_type(ppf, ty) {
                                 var single = tys.hd;
                                 if (typeof single !== "number" && single.TAG === /* Otyp_tuple */9) {
                                   if (tys.tl) {
-                                    throw {
-                                          MEL_EXN_ID: Stdlib.Not_found,
-                                          Error: new Error()
-                                        };
+                                    throw new Error(Stdlib.Not_found, {
+                                              cause: {
+                                                MEL_EXN_ID: Stdlib.Not_found
+                                              }
+                                            });
                                   }
                                   if (variant$1 === "Arity_1") {
                                     return {
@@ -40341,10 +41414,11 @@ function print_simple_out_type(ppf, ty) {
                                   }
                                 }
                                 if (tys.tl) {
-                                  throw {
-                                        MEL_EXN_ID: Stdlib.Not_found,
-                                        Error: new Error()
-                                      };
+                                  throw new Error(Stdlib.Not_found, {
+                                            cause: {
+                                              MEL_EXN_ID: Stdlib.Not_found
+                                            }
+                                          });
                                 }
                                 return {
                                         TAG: /* Otyp_arrow */1,
@@ -40353,10 +41427,11 @@ function print_simple_out_type(ppf, ty) {
                                         _2: result
                                       };
                               }
-                              throw {
-                                    MEL_EXN_ID: Stdlib.Not_found,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Stdlib.Not_found, {
+                                        cause: {
+                                          MEL_EXN_ID: Stdlib.Not_found
+                                        }
+                                      });
                             };
                             var exit$4 = 0;
                             var res$1;
@@ -40481,15 +41556,16 @@ function print_simple_out_type(ppf, ty) {
                                                     _1: "@[<0>(%a@ [@mel.meth])@]"
                                                   }), print_out_type_1, res$1);
                                 default:
-                                  throw {
-                                        MEL_EXN_ID: "Assert_failure",
-                                        _1: [
-                                          "jscomp/test/ocaml_typedtree_test.ml",
-                                          34910,
-                                          17
-                                        ],
-                                        Error: new Error()
-                                      };
+                                  throw new Error("Assert_failure", {
+                                            cause: {
+                                              MEL_EXN_ID: "Assert_failure",
+                                              _1: [
+                                                "jscomp/test/ocaml_typedtree_test.ml",
+                                                34910,
+                                                17
+                                              ]
+                                            }
+                                          });
                               }
                             }
                             
@@ -41563,41 +42639,45 @@ var out_class_type = {
 
 var out_module_type = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "Oprint.out_module_type",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "Oprint.out_module_type"
+                }
+              });
     })
 };
 
 var out_sig_item = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "Oprint.out_sig_item",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "Oprint.out_sig_item"
+                }
+              });
     })
 };
 
 var out_signature = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "Oprint.out_signature",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "Oprint.out_signature"
+                }
+              });
     })
 };
 
 var out_type_extension = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "Oprint.out_type_extension",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "Oprint.out_type_extension"
+                }
+              });
     })
 };
 
@@ -43529,7 +44609,9 @@ function ident_name(id) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return id.name;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -43544,7 +44626,9 @@ function add_unique(id) {
       unique_names.contents = add(id, unique_toplevel_name(id), unique_names.contents);
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -45303,17 +46387,19 @@ function bal$6(l, x, d, r) {
       if (lr) {
         return create$7(create$7(ll, lv, ld, lr.l), lr.v, lr.d, create$7(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -45335,17 +46421,19 @@ function bal$6(l, x, d, r) {
     if (rl) {
       return create$7(create$7(l, x, d, rl.l), rl.v, rl.d, create$7(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add$8(x, data, m) {
@@ -45403,10 +46491,11 @@ function find$4(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -45426,10 +46515,11 @@ function index(l, x) {
       return 1 + index(l.tl, x) | 0;
     }
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function uniq(_param) {
@@ -45502,7 +46592,9 @@ function normalize_type_path(cacheOpt, env, p) {
               /* Id */0
             ];
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -45594,7 +46686,9 @@ function set_printing_env(env) {
                 }, printing_map.contents);
             return ;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
       });
   var cont = function (param) {
@@ -45682,10 +46776,11 @@ function best_type_path(p) {
               }), l);
         continue ;
       }
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     };
   };
   while((function () {
@@ -45701,7 +46796,9 @@ function best_type_path(p) {
               if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                 tmp$1 = true;
               } else {
-                throw exn;
+                throw new Error(exn.MEL_EXN_ID, {
+                          cause: exn
+                        });
               }
             }
             tmp = tmp$1;
@@ -45722,7 +46819,9 @@ function best_type_path(p) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       p$p$p = p$p;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   return [
@@ -45846,7 +46945,9 @@ function name_of_type(t) {
       }
       return name;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -46395,15 +47496,16 @@ function tree_of_typobject(sch, fi, nm) {
           }), match.tl);
     var match$1 = best_type_path(nm[0]);
     if (!Caml_obj.caml_equal(match$1[1], /* Id */0)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              36171,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    36171,
+                    6
+                  ]
+                }
+              });
     }
     return {
             TAG: /* Otyp_class */2,
@@ -48081,15 +49183,16 @@ function mismatch(unif, param) {
       return ;
     }
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          36822,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                36822,
+                9
+              ]
+            }
+          });
 }
 
 function explanation(unif, mis, ppf) {
@@ -49166,29 +50269,33 @@ function report_unification_error(ppf, env, unifOpt, tr, txt1, txt2) {
               }
               catch (exn){
                 print_labels.contents = true;
-                throw exn;
+                throw new Error(exn.MEL_EXN_ID, {
+                          cause: exn
+                        });
               }
             } else {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      36921,
-                      20
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            36921,
+                            20
+                          ]
+                        }
+                      });
             }
           } else {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    36921,
-                    20
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          36921,
+                          20
+                        ]
+                      }
+                    });
           }
         }));
 }
@@ -49221,7 +50328,9 @@ function trace$1(fst, keep_last, txt, ppf, tr) {
   }
   catch (exn){
     print_labels.contents = true;
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -50015,7 +51124,9 @@ function type_manifest(env, ty1, params1, ty2, params2, priv2) {
       if (exn.MEL_EXN_ID === Cannot_expand) {
         return false;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   return check_super(ty1);
@@ -50689,7 +51800,9 @@ function scrape(env, mty) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return mty;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -50983,10 +52096,11 @@ function nondep_supertype(env, mid, mty) {
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
               if (va) {
-                throw {
-                      MEL_EXN_ID: Stdlib.Not_found,
-                      Error: new Error()
-                    };
+                throw new Error(Stdlib.Not_found, {
+                          cause: {
+                            MEL_EXN_ID: Stdlib.Not_found
+                          }
+                        });
               }
               return {
                       hd: {
@@ -51001,7 +52115,9 @@ function nondep_supertype(env, mid, mty) {
                       tl: rem$p
                     };
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
       case /* Sig_class */5 :
           return {
@@ -51073,7 +52189,9 @@ function enrich_typedecl(env, p, decl) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return decl;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -51197,20 +52315,24 @@ function contains_type(env, _param) {
             if (mty !== undefined) {
               return contains_type(env, mty);
             }
-            throw {
-                  MEL_EXN_ID: Stdlib.Exit,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Exit, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Exit
+                      }
+                    });
           }
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-              throw {
-                    MEL_EXN_ID: Stdlib.Exit,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Exit, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Exit
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
       case /* Mty_signature */1 :
           return contains_type_sig(env)(param._0);
@@ -51241,22 +52363,25 @@ function contains_type_sig(env) {
                           if (match.type_private) {
                             return ;
                           }
-                          throw {
-                                MEL_EXN_ID: Stdlib.Exit,
-                                Error: new Error()
-                              };
+                          throw new Error(Stdlib.Exit, {
+                                    cause: {
+                                      MEL_EXN_ID: Stdlib.Exit
+                                    }
+                                  });
                         }
-                        throw {
-                              MEL_EXN_ID: Stdlib.Exit,
-                              Error: new Error()
-                            };
+                        throw new Error(Stdlib.Exit, {
+                                  cause: {
+                                    MEL_EXN_ID: Stdlib.Exit
+                                  }
+                                });
                     case /* Sig_module */3 :
                         return contains_type(env, param._1.md_type);
                     case /* Sig_modtype */4 :
-                        throw {
-                              MEL_EXN_ID: Stdlib.Exit,
-                              Error: new Error()
-                            };
+                        throw new Error(Stdlib.Exit, {
+                                  cause: {
+                                    MEL_EXN_ID: Stdlib.Exit
+                                  }
+                                });
                     default:
                       return ;
                   }
@@ -51274,7 +52399,9 @@ function contains_type$1(env, mty) {
     if (exn.MEL_EXN_ID === Stdlib.Exit) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -51323,17 +52450,19 @@ function bal$7(l, v, r) {
       if (lr) {
         return create$8(create$8(ll, lv, lr.l), lr.v, create$8(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -51353,17 +52482,19 @@ function bal$7(l, v, r) {
     if (rl) {
       return create$8(create$8(l, v, rl.l), rl.v, create$8(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$9(x, t) {
@@ -51549,17 +52680,19 @@ function bal$8(l, x, d, r) {
       if (lr) {
         return create$9(create$9(ll, lv, ld, lr.l), lr.v, lr.d, create$9(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -51581,17 +52714,19 @@ function bal$8(l, x, d, r) {
     if (rl) {
       return create$9(create$9(l, x, d, rl.l), rl.v, rl.d, create$9(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add$10(x, data, m) {
@@ -51649,10 +52784,11 @@ function find$5(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -51695,17 +52831,19 @@ function bal$9(l, v, r) {
       if (lr) {
         return create$10(create$10(ll, lv, lr.l), lr.v, create$10(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -51725,17 +52863,19 @@ function bal$9(l, v, r) {
     if (rl) {
       return create$10(create$10(l, v, rl.l), rl.v, create$10(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$11(x, t) {
@@ -51950,7 +53090,9 @@ function rollback_path(subst, _p) {
           
         }
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
   };
@@ -51970,7 +53112,9 @@ function collect_ids(subst, bindings, p) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             ids = /* Empty */0;
           } else {
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }
         return Curry._2(add$11, id$1, ids);
@@ -52153,10 +53297,11 @@ function value_descriptions(env, cxt, subst, id, vd1, vd2) {
         if (Caml_obj.caml_equal(p1, match$1._0)) {
           return /* Tcoerce_none */0;
         }
-        throw {
-              MEL_EXN_ID: Dont_match,
-              Error: new Error()
-            };
+        throw new Error(Dont_match, {
+                  cause: {
+                    MEL_EXN_ID: Dont_match
+                  }
+                });
       }
       if (typeof match$1 === "number") {
         return /* Tcoerce_none */0;
@@ -52164,39 +53309,44 @@ function value_descriptions(env, cxt, subst, id, vd1, vd2) {
       if (match$1.TAG !== /* Val_prim */0) {
         return /* Tcoerce_none */0;
       }
-      throw {
-            MEL_EXN_ID: Dont_match,
-            Error: new Error()
-          };
+      throw new Error(Dont_match, {
+                cause: {
+                  MEL_EXN_ID: Dont_match
+                }
+              });
     } else {
-      throw {
-            MEL_EXN_ID: Dont_match,
-            Error: new Error()
-          };
+      throw new Error(Dont_match, {
+                cause: {
+                  MEL_EXN_ID: Dont_match
+                }
+              });
     }
   }
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Dont_match) {
-      throw {
-            MEL_EXN_ID: $$Error$5,
-            _1: {
-              hd: [
-                cxt,
-                env,
-                {
-                  TAG: /* Value_descriptions */1,
-                  _0: id,
-                  _1: vd1,
-                  _2: vd2$1
+      throw new Error($$Error$5, {
+                cause: {
+                  MEL_EXN_ID: $$Error$5,
+                  _1: {
+                    hd: [
+                      cxt,
+                      env,
+                      {
+                        TAG: /* Value_descriptions */1,
+                        _0: id,
+                        _1: vd1,
+                        _2: vd2$1
+                      }
+                    ],
+                    tl: /* [] */0
+                  }
                 }
-              ],
-              tl: /* [] */0
-            },
-            Error: new Error()
-          };
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -52208,24 +53358,25 @@ function type_declarations$2(env, old_envOpt, cxt, subst, id, decl1, decl2) {
   if (!Caml_obj.caml_notequal(err, /* [] */0)) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: $$Error$5,
-        _1: {
-          hd: [
-            cxt,
-            old_env,
-            {
-              TAG: /* Type_declarations */2,
-              _0: id,
-              _1: decl1,
-              _2: decl2$1,
-              _3: err
+  throw new Error($$Error$5, {
+            cause: {
+              MEL_EXN_ID: $$Error$5,
+              _1: {
+                hd: [
+                  cxt,
+                  old_env,
+                  {
+                    TAG: /* Type_declarations */2,
+                    _0: id,
+                    _1: decl1,
+                    _2: decl2$1,
+                    _3: err
+                  }
+                ],
+                tl: /* [] */0
+              }
             }
-          ],
-          tl: /* [] */0
-        },
-        Error: new Error()
-      };
+          });
 }
 
 function extension_constructors$1(env, cxt, subst, id, ext1, ext2) {
@@ -52233,23 +53384,24 @@ function extension_constructors$1(env, cxt, subst, id, ext1, ext2) {
   if (extension_constructors(env, id, ext1, ext2$1)) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: $$Error$5,
-        _1: {
-          hd: [
-            cxt,
-            env,
-            {
-              TAG: /* Extension_constructors */3,
-              _0: id,
-              _1: ext1,
-              _2: ext2$1
+  throw new Error($$Error$5, {
+            cause: {
+              MEL_EXN_ID: $$Error$5,
+              _1: {
+                hd: [
+                  cxt,
+                  env,
+                  {
+                    TAG: /* Extension_constructors */3,
+                    _0: id,
+                    _1: ext1,
+                    _2: ext2$1
+                  }
+                ],
+                tl: /* [] */0
+              }
             }
-          ],
-          tl: /* [] */0
-        },
-        Error: new Error()
-      };
+          });
 }
 
 function class_type_declarations$1(old_env, env, cxt, subst, id, decl1, decl2) {
@@ -52258,24 +53410,25 @@ function class_type_declarations$1(old_env, env, cxt, subst, id, decl1, decl2) {
   if (!reason) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: $$Error$5,
-        _1: {
-          hd: [
-            cxt,
-            old_env,
-            {
-              TAG: /* Class_type_declarations */7,
-              _0: id,
-              _1: decl1,
-              _2: decl2$1,
-              _3: reason
+  throw new Error($$Error$5, {
+            cause: {
+              MEL_EXN_ID: $$Error$5,
+              _1: {
+                hd: [
+                  cxt,
+                  old_env,
+                  {
+                    TAG: /* Class_type_declarations */7,
+                    _0: id,
+                    _1: decl1,
+                    _2: decl2$1,
+                    _3: reason
+                  }
+                ],
+                tl: /* [] */0
+              }
             }
-          ],
-          tl: /* [] */0
-        },
-        Error: new Error()
-      };
+          });
 }
 
 function class_declarations$1(old_env, env, cxt, subst, id, decl1, decl2) {
@@ -52284,24 +53437,25 @@ function class_declarations$1(old_env, env, cxt, subst, id, decl1, decl2) {
   if (!reason) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: $$Error$5,
-        _1: {
-          hd: [
-            cxt,
-            old_env,
-            {
-              TAG: /* Class_declarations */8,
-              _0: id,
-              _1: decl1,
-              _2: decl2$1,
-              _3: reason
+  throw new Error($$Error$5, {
+            cause: {
+              MEL_EXN_ID: $$Error$5,
+              _1: {
+                hd: [
+                  cxt,
+                  old_env,
+                  {
+                    TAG: /* Class_declarations */8,
+                    _0: id,
+                    _1: decl1,
+                    _2: decl2$1,
+                    _3: reason
+                  }
+                ],
+                tl: /* [] */0
+              }
             }
-          ],
-          tl: /* [] */0
-        },
-        Error: new Error()
-      };
+          });
 }
 
 var Dont_match$1 = /* @__PURE__ */Caml_exceptions.create("Ocaml_typedtree_test.Includemod.Dont_match");
@@ -52316,7 +53470,9 @@ function may_expand_module_path(env, path) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -52327,23 +53483,26 @@ function expand_module_path(env, cxt, path) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: $$Error$5,
-            _1: {
-              hd: [
-                cxt,
-                env,
-                {
-                  TAG: /* Unbound_modtype_path */9,
-                  _0: path
+      throw new Error($$Error$5, {
+                cause: {
+                  MEL_EXN_ID: $$Error$5,
+                  _1: {
+                    hd: [
+                      cxt,
+                      env,
+                      {
+                        TAG: /* Unbound_modtype_path */9,
+                        _0: path
+                      }
+                    ],
+                    tl: /* [] */0
+                  }
                 }
-              ],
-              tl: /* [] */0
-            },
-            Error: new Error()
-          };
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -52354,23 +53513,26 @@ function expand_module_alias(env, cxt, path) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: $$Error$5,
-            _1: {
-              hd: [
-                cxt,
-                env,
-                {
-                  TAG: /* Unbound_module_path */10,
-                  _0: path
+      throw new Error($$Error$5, {
+                cause: {
+                  MEL_EXN_ID: $$Error$5,
+                  _1: {
+                    hd: [
+                      cxt,
+                      env,
+                      {
+                        TAG: /* Unbound_module_path */10,
+                        _0: path
+                      }
+                    ],
+                    tl: /* [] */0
+                  }
                 }
-              ],
-              tl: /* [] */0
-            },
-            Error: new Error()
-          };
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -52495,48 +53657,56 @@ function modtypes(env, cxt, subst, mty1, mty2) {
   catch (raw_err){
     var err = Caml_js_exceptions.internalToOCamlException(raw_err);
     if (err.MEL_EXN_ID === Dont_match$1) {
-      throw {
-            MEL_EXN_ID: $$Error$5,
-            _1: {
-              hd: [
-                cxt,
-                env,
-                {
-                  TAG: /* Module_types */4,
-                  _0: mty1,
-                  _1: modtype(subst, mty2)
+      throw new Error($$Error$5, {
+                cause: {
+                  MEL_EXN_ID: $$Error$5,
+                  _1: {
+                    hd: [
+                      cxt,
+                      env,
+                      {
+                        TAG: /* Module_types */4,
+                        _0: mty1,
+                        _1: modtype(subst, mty2)
+                      }
+                    ],
+                    tl: /* [] */0
+                  }
                 }
-              ],
-              tl: /* [] */0
-            },
-            Error: new Error()
-          };
+              });
     }
     if (err.MEL_EXN_ID === $$Error$5) {
       if (mty1.TAG === /* Mty_alias */3) {
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       if (mty2.TAG === /* Mty_alias */3) {
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
-      throw {
-            MEL_EXN_ID: $$Error$5,
-            _1: {
-              hd: [
-                cxt,
-                env,
-                {
-                  TAG: /* Module_types */4,
-                  _0: mty1,
-                  _1: modtype(subst, mty2)
+      throw new Error($$Error$5, {
+                cause: {
+                  MEL_EXN_ID: $$Error$5,
+                  _1: {
+                    hd: [
+                      cxt,
+                      env,
+                      {
+                        TAG: /* Module_types */4,
+                        _0: mty1,
+                        _1: modtype(subst, mty2)
+                      }
+                    ],
+                    tl: err._1
+                  }
                 }
-              ],
-              tl: err._1
-            },
-            Error: new Error()
-          };
+              });
     }
-    throw err;
+    throw new Error(err.MEL_EXN_ID, {
+              cause: err
+            });
   }
 }
 
@@ -52559,10 +53729,11 @@ function try_modtypes(env, cxt, subst, _mty1, mty2) {
                 return signatures(env, cxt, subst, mty1._0, mty2._0);
             case /* Mty_functor */2 :
             case /* Mty_alias */3 :
-                throw {
-                      MEL_EXN_ID: Dont_match$1,
-                      Error: new Error()
-                    };
+                throw new Error(Dont_match$1, {
+                          cause: {
+                            MEL_EXN_ID: Dont_match$1
+                          }
+                        });
             
           }
           break;
@@ -52604,16 +53775,18 @@ function try_modtypes(env, cxt, subst, _mty1, mty2) {
                             };
                     }
                   }
-                  throw {
-                        MEL_EXN_ID: Dont_match$1,
-                        Error: new Error()
-                      };
+                  throw new Error(Dont_match$1, {
+                            cause: {
+                              MEL_EXN_ID: Dont_match$1
+                            }
+                          });
               case /* Mty_signature */1 :
               case /* Mty_alias */3 :
-                  throw {
-                        MEL_EXN_ID: Dont_match$1,
-                        Error: new Error()
-                      };
+                  throw new Error(Dont_match$1, {
+                            cause: {
+                              MEL_EXN_ID: Dont_match$1
+                            }
+                          });
               
             }
           } else {
@@ -52622,10 +53795,11 @@ function try_modtypes(env, cxt, subst, _mty1, mty2) {
                   break;
               case /* Mty_functor */2 :
                   if (mty2._1 !== undefined) {
-                    throw {
-                          MEL_EXN_ID: Dont_match$1,
-                          Error: new Error()
-                        };
+                    throw new Error(Dont_match$1, {
+                              cause: {
+                                MEL_EXN_ID: Dont_match$1
+                              }
+                            });
                   }
                   var cc = modtypes(env, {
                         hd: {
@@ -52645,10 +53819,11 @@ function try_modtypes(env, cxt, subst, _mty1, mty2) {
                   }
               case /* Mty_signature */1 :
               case /* Mty_alias */3 :
-                  throw {
-                        MEL_EXN_ID: Dont_match$1,
-                        Error: new Error()
-                      };
+                  throw new Error(Dont_match$1, {
+                            cause: {
+                              MEL_EXN_ID: Dont_match$1
+                            }
+                          });
               
             }
           }
@@ -52658,21 +53833,22 @@ function try_modtypes(env, cxt, subst, _mty1, mty2) {
           if (mty2.TAG === /* Mty_alias */3) {
             var p2 = mty2._0;
             if (is_functor_arg(p2, env)) {
-              throw {
-                    MEL_EXN_ID: $$Error$5,
-                    _1: {
-                      hd: [
-                        cxt,
-                        env,
-                        {
-                          TAG: /* Invalid_module_alias */11,
-                          _0: p2
+              throw new Error($$Error$5, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$5,
+                          _1: {
+                            hd: [
+                              cxt,
+                              env,
+                              {
+                                TAG: /* Invalid_module_alias */11,
+                                _0: p2
+                              }
+                            ],
+                            tl: /* [] */0
+                          }
                         }
-                      ],
-                      tl: /* [] */0
-                    },
-                    Error: new Error()
-                  };
+                      });
             }
             if (same(p1$1, p2)) {
               return /* Tcoerce_none */0;
@@ -52682,10 +53858,11 @@ function try_modtypes(env, cxt, subst, _mty1, mty2) {
             if (same(p1$2, p2$1)) {
               return /* Tcoerce_none */0;
             }
-            throw {
-                  MEL_EXN_ID: Dont_match$1,
-                  Error: new Error()
-                };
+            throw new Error(Dont_match$1, {
+                      cause: {
+                        MEL_EXN_ID: Dont_match$1
+                      }
+                    });
           }
           var p1$3;
           try {
@@ -52696,25 +53873,30 @@ function try_modtypes(env, cxt, subst, _mty1, mty2) {
             if (exn.MEL_EXN_ID === $$Error$2) {
               var match = exn._1;
               if (match.TAG === /* Missing_module */3) {
-                throw {
-                      MEL_EXN_ID: $$Error$5,
-                      _1: {
-                        hd: [
-                          cxt,
-                          env,
-                          {
-                            TAG: /* Unbound_module_path */10,
-                            _0: match._2
+                throw new Error($$Error$5, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$5,
+                            _1: {
+                              hd: [
+                                cxt,
+                                env,
+                                {
+                                  TAG: /* Unbound_module_path */10,
+                                  _0: match._2
+                                }
+                              ],
+                              tl: /* [] */0
+                            }
                           }
-                        ],
-                        tl: /* [] */0
-                      },
-                      Error: new Error()
-                    };
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           var mty1$1 = strengthen$1(env, expand_module_alias(env, cxt, p1$3), p1$3);
           return {
@@ -52733,34 +53915,37 @@ function try_modtypes(env, cxt, subst, _mty1, mty2) {
           }
           
         } else {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  38374,
-                  6
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        38374,
+                        6
+                      ]
+                    }
+                  });
         }
       }
       if (mty2$1.TAG === /* Mty_ident */0) {
         return try_modtypes(env, cxt, identity, mty1, expand_module_path(env, cxt, mty2$1._0));
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              38374,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    38374,
+                    6
+                  ]
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: Dont_match$1,
-          Error: new Error()
-        };
+    throw new Error(Dont_match$1, {
+              cause: {
+                MEL_EXN_ID: Dont_match$1
+              }
+            });
   };
 }
 
@@ -52915,15 +54100,18 @@ function signatures(env, cxt, subst, sig1, sig2) {
             _unpaired = unpaired$1;
             continue ;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
       } else {
         if (unpaired) {
-          throw {
-                MEL_EXN_ID: $$Error$5,
-                _1: unpaired,
-                Error: new Error()
-              };
+          throw new Error($$Error$5, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$5,
+                      _1: unpaired
+                    }
+                  });
         }
         var cc = signature_components(env, new_env, cxt, subst, Stdlib__List.rev(paired));
         if (len1 === len2) {
@@ -53071,15 +54259,16 @@ function signature_components(old_env, env, cxt, subst, paired) {
         break;
     
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          38499,
-          6
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                38499,
+                6
+              ]
+            }
+          });
 }
 
 function modtype_infos(env, cxt, subst, id, info1, info2) {
@@ -53116,25 +54305,28 @@ function modtype_infos(env, cxt, subst, id, info1, info2) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === $$Error$5) {
-      throw {
-            MEL_EXN_ID: $$Error$5,
-            _1: {
-              hd: [
-                cxt,
-                env,
-                {
-                  TAG: /* Modtype_infos */5,
-                  _0: id,
-                  _1: info1,
-                  _2: info2$1
+      throw new Error($$Error$5, {
+                cause: {
+                  MEL_EXN_ID: $$Error$5,
+                  _1: {
+                    hd: [
+                      cxt,
+                      env,
+                      {
+                        TAG: /* Modtype_infos */5,
+                        _0: id,
+                        _1: info1,
+                        _2: info2$1
+                      }
+                    ],
+                    tl: exn._1
+                  }
                 }
-              ],
-              tl: exn._1
-            },
-            Error: new Error()
-          };
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -53144,18 +54336,19 @@ function check_modtype_equiv(env, cxt, mty1, mty2) {
   if (typeof match === "number" && typeof match$1 === "number") {
     return ;
   }
-  throw {
-        MEL_EXN_ID: $$Error$5,
-        _1: {
-          hd: [
-            cxt,
-            env,
-            /* Modtype_permutation */0
-          ],
-          tl: /* [] */0
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$5, {
+            cause: {
+              MEL_EXN_ID: $$Error$5,
+              _1: {
+                hd: [
+                  cxt,
+                  env,
+                  /* Modtype_permutation */0
+                ],
+                tl: /* [] */0
+              }
+            }
+          });
 }
 
 function check_modtype_inclusion$1(env, mty1, path1, mty2) {
@@ -53166,12 +54359,15 @@ function check_modtype_inclusion$1(env, mty1, path1, mty2) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === $$Error$5) {
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -53184,24 +54380,27 @@ function compunit(env, impl_name, impl_sig, intf_name, intf_sig) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === $$Error$5) {
-      throw {
-            MEL_EXN_ID: $$Error$5,
-            _1: {
-              hd: [
-                /* [] */0,
-                empty,
-                {
-                  TAG: /* Interface_mismatch */6,
-                  _0: impl_name,
-                  _1: intf_name
+      throw new Error($$Error$5, {
+                cause: {
+                  MEL_EXN_ID: $$Error$5,
+                  _1: {
+                    hd: [
+                      /* [] */0,
+                      empty,
+                      {
+                        TAG: /* Interface_mismatch */6,
+                        _0: impl_name,
+                        _1: intf_name
+                      }
+                    ],
+                    tl: exn._1
+                  }
                 }
-              ],
-              tl: exn._1
-            },
-            Error: new Error()
-          };
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -54299,36 +55498,39 @@ function path_of_context(param) {
           };
           continue ;
         }
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                38670,
-                15
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      38670,
+                      15
+                    ]
+                  }
+                });
       };
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            38672,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  38672,
+                  9
+                ]
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          38672,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                38672,
+                9
+              ]
+            }
+          });
 }
 
 function context$1(ppf, cxt) {
@@ -54986,15 +56188,16 @@ function compat(_p, _q) {
           _q = match$1._1;
           continue ;
       case 3 :
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  39141,
-                  6
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        39141,
+                        6
+                      ]
+                    }
+                  });
       
     }
   };
@@ -55013,28 +56216,30 @@ function compats(_ps, _qs) {
         _ps = ps.tl;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              39146,
-              12
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    39146,
+                    12
+                  ]
+                }
+              });
     }
     if (!qs) {
       return true;
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            39146,
-            12
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  39146,
+                  12
+                ]
+              }
+            });
   };
 }
 
@@ -56167,7 +57372,9 @@ function simple_match_args(p1, _p2) {
                           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                             return omega;
                           }
-                          throw exn;
+                          throw new Error(exn.MEL_EXN_ID, {
+                                    cause: exn
+                                  });
                         }
                       }
                       }(arg$1)), omegas);
@@ -56351,7 +57558,9 @@ function discr_pat(q, pss) {
                                 tl: r
                               };
                       }
-                      throw exn;
+                      throw new Error(exn.MEL_EXN_ID, {
+                                cause: exn
+                              });
                     }
                   }), match$1._0, record_arg(acc));
             _pss = pss$1.tl;
@@ -56452,15 +57661,16 @@ function do_set_args(erase_mutable, q, r) {
               r.tl
             ];
           } else {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    39485,
-                    13
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          39485,
+                          13
+                        ]
+                      }
+                    });
           }
         } else {
           match$2 = [
@@ -56942,55 +58152,59 @@ function row_of_pat(pat) {
   var match = expand_head(pat.pat_env, pat.pat_type);
   var row = match.desc;
   if (typeof row === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            39637,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  39637,
+                  9
+                ]
+              }
+            });
   }
   if (row.TAG === /* Tvariant */8) {
     return row_repr_aux(/* [] */0, row._0);
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          39637,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                39637,
+                9
+              ]
+            }
+          });
 }
 
 function generalized_constructor(x) {
   var match = x[0].pat_desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            39648,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  39648,
+                  9
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tpat_construct */4) {
     return match._1.cstr_generalized;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          39648,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                39648,
+                9
+              ]
+            }
+          });
 }
 
 function clean_env(env) {
@@ -57045,28 +58259,30 @@ function full_match(ignore_generalized, closing, env) {
         var fields = Stdlib__List.map((function (param) {
                 var match = param[0].pat_desc;
                 if (typeof match === "number") {
-                  throw {
-                        MEL_EXN_ID: "Assert_failure",
-                        _1: [
-                          "jscomp/test/ocaml_typedtree_test.ml",
-                          39675,
-                          17
-                        ],
-                        Error: new Error()
-                      };
+                  throw new Error("Assert_failure", {
+                            cause: {
+                              MEL_EXN_ID: "Assert_failure",
+                              _1: [
+                                "jscomp/test/ocaml_typedtree_test.ml",
+                                39675,
+                                17
+                              ]
+                            }
+                          });
                 }
                 if (match.TAG === /* Tpat_variant */5) {
                   return match._0;
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        39675,
-                        17
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              39675,
+                              17
+                            ]
+                          }
+                        });
               }), env);
         var row = row_of_pat(p);
         if (closing && !row_fixed(row)) {
@@ -57153,15 +58369,16 @@ function complete_tags(nconsts, nconstrs, tags) {
             case /* Cstr_block */1 :
                 return Caml_array.set(seen_constr, param._0, true);
             case /* Cstr_extension */2 :
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        39738,
-                        14
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              39738,
+                              14
+                            ]
+                          }
+                        });
             
           }
         }), tags);
@@ -57236,10 +58453,11 @@ function pat_of_constrs(ex_pat, param) {
       return pat_of_constr(ex_pat, cstr);
     }
   }
-  throw {
-        MEL_EXN_ID: Empty,
-        Error: new Error()
-      };
+  throw new Error(Empty, {
+            cause: {
+              MEL_EXN_ID: Empty
+            }
+          });
 }
 
 function get_variant_constructors(env, _ty) {
@@ -57342,15 +58560,16 @@ function build_other(ext, env) {
                               }
                               
                             }
-                            throw {
-                                  MEL_EXN_ID: "Assert_failure",
-                                  _1: [
-                                    "jscomp/test/ocaml_typedtree_test.ml",
-                                    39892,
-                                    55
-                                  ],
-                                  Error: new Error()
-                                };
+                            throw new Error("Assert_failure", {
+                                      cause: {
+                                        MEL_EXN_ID: "Assert_failure",
+                                        _1: [
+                                          "jscomp/test/ocaml_typedtree_test.ml",
+                                          39892,
+                                          55
+                                        ]
+                                      }
+                                    });
                           }), (function (i) {
                             return {
                                     TAG: /* Tpat_constant */2,
@@ -57372,15 +58591,16 @@ function build_other(ext, env) {
                         }
                         
                       }
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              39867,
-                              15
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    39867,
+                                    15
+                                  ]
+                                }
+                              });
                     }), env);
               var _param = {
                 hd: [
@@ -57425,10 +58645,11 @@ function build_other(ext, env) {
                   while(true) {
                     var i = _i;
                     if (i > imax) {
-                      throw {
-                            MEL_EXN_ID: Stdlib.Not_found,
-                            Error: new Error()
-                          };
+                      throw new Error(Stdlib.Not_found, {
+                                cause: {
+                                  MEL_EXN_ID: Stdlib.Not_found
+                                }
+                              });
                     }
                     var ci = Stdlib__Char.chr(i);
                     if (!Stdlib__List.mem(ci, all_chars)) {
@@ -57450,7 +58671,9 @@ function build_other(ext, env) {
                     _param = param.tl;
                     continue ;
                   }
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
               };
           case /* Const_string */2 :
@@ -57462,15 +58685,16 @@ function build_other(ext, env) {
                               }
                               
                             }
-                            throw {
-                                  MEL_EXN_ID: "Assert_failure",
-                                  _1: [
-                                    "jscomp/test/ocaml_typedtree_test.ml",
-                                    39913,
-                                    21
-                                  ],
-                                  Error: new Error()
-                                };
+                            throw new Error("Assert_failure", {
+                                      cause: {
+                                        MEL_EXN_ID: "Assert_failure",
+                                        _1: [
+                                          "jscomp/test/ocaml_typedtree_test.ml",
+                                          39913,
+                                          21
+                                        ]
+                                      }
+                                    });
                           }), (function (i) {
                             return {
                                     TAG: /* Tpat_constant */2,
@@ -57492,15 +58716,16 @@ function build_other(ext, env) {
                               }
                               
                             }
-                            throw {
-                                  MEL_EXN_ID: "Assert_failure",
-                                  _1: [
-                                    "jscomp/test/ocaml_typedtree_test.ml",
-                                    39919,
-                                    21
-                                  ],
-                                  Error: new Error()
-                                };
+                            throw new Error("Assert_failure", {
+                                      cause: {
+                                        MEL_EXN_ID: "Assert_failure",
+                                        _1: [
+                                          "jscomp/test/ocaml_typedtree_test.ml",
+                                          39919,
+                                          21
+                                        ]
+                                      }
+                                    });
                           }), (function (f) {
                             return {
                                     TAG: /* Tpat_constant */2,
@@ -57521,15 +58746,16 @@ function build_other(ext, env) {
                               }
                               
                             }
-                            throw {
-                                  MEL_EXN_ID: "Assert_failure",
-                                  _1: [
-                                    "jscomp/test/ocaml_typedtree_test.ml",
-                                    39897,
-                                    57
-                                  ],
-                                  Error: new Error()
-                                };
+                            throw new Error("Assert_failure", {
+                                      cause: {
+                                        MEL_EXN_ID: "Assert_failure",
+                                        _1: [
+                                          "jscomp/test/ocaml_typedtree_test.ml",
+                                          39897,
+                                          57
+                                        ]
+                                      }
+                                    });
                           }), (function (i) {
                             return {
                                     TAG: /* Tpat_constant */2,
@@ -57548,15 +58774,16 @@ function build_other(ext, env) {
                               }
                               
                             }
-                            throw {
-                                  MEL_EXN_ID: "Assert_failure",
-                                  _1: [
-                                    "jscomp/test/ocaml_typedtree_test.ml",
-                                    39902,
-                                    57
-                                  ],
-                                  Error: new Error()
-                                };
+                            throw new Error("Assert_failure", {
+                                      cause: {
+                                        MEL_EXN_ID: "Assert_failure",
+                                        _1: [
+                                          "jscomp/test/ocaml_typedtree_test.ml",
+                                          39902,
+                                          57
+                                        ]
+                                      }
+                                    });
                           }), (function (i) {
                             return {
                                     TAG: /* Tpat_constant */2,
@@ -57567,15 +58794,16 @@ function build_other(ext, env) {
                                   };
                           }), Caml_int64.zero, Stdlib__Int64.succ, p, env);
           case /* Const_nativeint */6 :
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      39909,
-                      33
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            39909,
+                            33
+                          ]
+                        }
+                      });
           
         }
     case /* Tpat_construct */4 :
@@ -57652,28 +58880,30 @@ function build_other(ext, env) {
         var tags = Stdlib__List.map((function (param) {
                 var match = param[0].pat_desc;
                 if (typeof match === "number") {
-                  throw {
-                        MEL_EXN_ID: "Assert_failure",
-                        _1: [
-                          "jscomp/test/ocaml_typedtree_test.ml",
-                          39836,
-                          23
-                        ],
-                        Error: new Error()
-                      };
+                  throw new Error("Assert_failure", {
+                            cause: {
+                              MEL_EXN_ID: "Assert_failure",
+                              _1: [
+                                "jscomp/test/ocaml_typedtree_test.ml",
+                                39836,
+                                23
+                              ]
+                            }
+                          });
                 }
                 if (match.TAG === /* Tpat_variant */5) {
                   return match._0;
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        39836,
-                        23
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              39836,
+                              23
+                            ]
+                          }
+                        });
               }), env);
         var row = row_of_pat(p);
         var make_other_pat = function (tag, $$const) {
@@ -57721,28 +58951,30 @@ function build_other(ext, env) {
         var all_lengths = Stdlib__List.map((function (param) {
                 var args = param[0].pat_desc;
                 if (typeof args === "number") {
-                  throw {
-                        MEL_EXN_ID: "Assert_failure",
-                        _1: [
-                          "jscomp/test/ocaml_typedtree_test.ml",
-                          39928,
-                          15
-                        ],
-                        Error: new Error()
-                      };
+                  throw new Error("Assert_failure", {
+                            cause: {
+                              MEL_EXN_ID: "Assert_failure",
+                              _1: [
+                                "jscomp/test/ocaml_typedtree_test.ml",
+                                39928,
+                                15
+                              ]
+                            }
+                          });
                 }
                 if (args.TAG === /* Tpat_array */7) {
                   return Stdlib__List.length(args._0);
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        39928,
-                        15
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              39928,
+                              15
+                            ]
+                          }
+                        });
               }), env);
         var _l = 0;
         while(true) {
@@ -57782,15 +59014,16 @@ function build_other_gadt(ext, env) {
     }
     
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          39952,
-          11
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                39952,
+                11
+              ]
+            }
+          });
 }
 
 function has_instance(_p) {
@@ -57945,15 +59178,16 @@ function orify_many(param) {
       return x;
     }
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          40024,
-          12
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                40024,
+                12
+              ]
+            }
+          });
 }
 
 function try_many_gadt(f, param) {
@@ -58041,7 +59275,9 @@ function exhaust(ext, pss, n) {
       if (exn.MEL_EXN_ID === Empty) {
         return fatal_error("Parmatch.exhaust");
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   } else {
     var r$2 = exhaust(ext, filter_extra(pss), n - 1 | 0);
@@ -58141,7 +59377,9 @@ function exhaust_gadt(ext, pss, n) {
       if (exn.MEL_EXN_ID === Empty) {
         return fatal_error("Parmatch.exhaust");
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   } else {
     var r$1 = exhaust_gadt(ext, filter_extra(pss), n - 1 | 0);
@@ -58174,27 +59412,29 @@ function exhaust_gadt$1(ext, pss, n) {
   var singletons = Stdlib__List.map((function (param) {
           if (param) {
             if (param.tl) {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      40200,
-                      19
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            40200,
+                            19
+                          ]
+                        }
+                      });
             }
             return param.hd;
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  40200,
-                  19
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        40200,
+                        19
+                      ]
+                    }
+                  });
         }), lst);
   return /* Rsome */{
           _0: {
@@ -58295,15 +59535,16 @@ function is_var_column(rs) {
                     return false;
                   }
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        40309,
-                        14
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              40309,
+                              14
+                            ]
+                          }
+                        });
               }), rs);
 }
 
@@ -58312,15 +59553,16 @@ function or_args(_p) {
     var p = _p;
     var match = p.pat_desc;
     if (typeof match === "number") {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              40316,
-              23
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    40316,
+                    23
+                  ]
+                }
+              });
     }
     switch (match.TAG | 0) {
       case /* Tpat_alias */1 :
@@ -58332,15 +59574,16 @@ function or_args(_p) {
                   match._1
                 ];
       default:
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                40316,
-                23
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      40316,
+                      23
+                    ]
+                  }
+                });
     }
   };
 }
@@ -58354,15 +59597,16 @@ function remove$1(r) {
             active: match.tl
           };
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          40321,
-          12
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                40321,
+                12
+              ]
+            }
+          });
 }
 
 function push_no_or(r) {
@@ -58377,15 +59621,16 @@ function push_no_or(r) {
             active: match.tl
           };
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          40328,
-          8
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                40328,
+                8
+              ]
+            }
+          });
 }
 
 function push_or(r) {
@@ -58400,15 +59645,16 @@ function push_or(r) {
             active: match.tl
           };
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          40332,
-          8
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                40332,
+                8
+              ]
+            }
+          });
 }
 
 function discr_pat$1(q, rs) {
@@ -58486,15 +59732,16 @@ function filter_one$1(q, rs) {
         _rs = rem;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              40349,
-              14
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    40349,
+                    14
+                  ]
+                }
+              });
     };
   };
   return filter_rec(rs);
@@ -58548,15 +59795,16 @@ function extract_columns(pss, qs) {
                                 }), param, param$1);
                   }), i, rs.tl);
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            40392,
-            8
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  40392,
+                  8
+                ]
+              }
+            });
   } else {
     return Stdlib__List.map((function (param) {
                   return /* [] */0;
@@ -58631,15 +59879,16 @@ function every_satisfiables(_pss, _qs) {
                       var match = qs.active;
                       if (match) {
                         if (match.tl) {
-                          throw {
-                                MEL_EXN_ID: "Assert_failure",
-                                _1: [
-                                  "jscomp/test/ocaml_typedtree_test.ml",
-                                  40429,
-                                  23
-                                ],
-                                Error: new Error()
-                              };
+                          throw new Error("Assert_failure", {
+                                    cause: {
+                                      MEL_EXN_ID: "Assert_failure",
+                                      _1: [
+                                        "jscomp/test/ocaml_typedtree_test.ml",
+                                        40429,
+                                        23
+                                      ]
+                                    }
+                                  });
                         }
                         var match$1 = or_args(match.hd);
                         var r_loc = every_both(pss, qs, match$1[0], match$1[1]);
@@ -58665,15 +59914,16 @@ function every_satisfiables(_pss, _qs) {
                           return r_loc;
                         }
                       }
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              40429,
-                              23
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    40429,
+                                    23
+                                  ]
+                                }
+                              });
                     }), extract_columns(pss, qs), extract_elements(qs), /* Used */0);
       } else if (satisfiable(Stdlib__List.map(make_vector, pss), qs.no_ors)) {
         return /* Used */0;
@@ -59035,10 +60285,11 @@ function initial_all(no_guard, param) {
   if (!no_guard) {
     return /* [] */0;
   }
-  throw {
-        MEL_EXN_ID: NoGuard,
-        Error: new Error()
-      };
+  throw new Error(NoGuard, {
+            cause: {
+              MEL_EXN_ID: NoGuard
+            }
+          });
 }
 
 function do_filter_var(param) {
@@ -59190,7 +60441,9 @@ function check_partial_all(v, casel) {
     if (exn.MEL_EXN_ID === NoGuard) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -59298,15 +60551,16 @@ function conv(typed) {
                                     _0: lst
                                   }) : lst.hd;
                           } else {
-                            throw {
-                                  MEL_EXN_ID: "Assert_failure",
-                                  _1: [
-                                    "jscomp/test/ocaml_typedtree_test.ml",
-                                    40764,
-                                    28
-                                  ],
-                                  Error: new Error()
-                                };
+                            throw new Error("Assert_failure", {
+                                      cause: {
+                                        MEL_EXN_ID: "Assert_failure",
+                                        _1: [
+                                          "jscomp/test/ocaml_typedtree_test.ml",
+                                          40764,
+                                          28
+                                        ]
+                                      }
+                                    });
                           }
                           return mk$1(undefined, undefined, {
                                       TAG: /* Ppat_construct */5,
@@ -59877,15 +61131,16 @@ function warning_leave_scope(param) {
     warning_scope.contents = match.tl;
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          41342,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                41342,
+                10
+              ]
+            }
+          });
 }
 
 function warning_attribute(attrs) {
@@ -59910,7 +61165,9 @@ function warning_attribute(attrs) {
                     _1: "Ill-formed list of warnings"
                   });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   Stdlib__List.iter((function (param) {
@@ -59956,15 +61213,18 @@ function narrow_unbound_lid_error(env, loc, lid, make_error) {
                     }));
       }
       if (exn.MEL_EXN_ID === Recmodule) {
-        throw {
-              MEL_EXN_ID: $$Error$6,
-              _1: loc,
-              _2: env,
-              _3: /* Illegal_reference_to_recursive_module */1,
-              Error: new Error()
-            };
+        throw new Error($$Error$6, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$6,
+                    _1: loc,
+                    _2: env,
+                    _3: /* Illegal_reference_to_recursive_module */1
+                  }
+                });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   switch (lid.TAG | 0) {
@@ -59976,40 +61236,43 @@ function narrow_unbound_lid_error(env, loc, lid, make_error) {
         var md = find_module(false, lookup_module(true, mlid, env), env);
         var match = scrape_alias(env, undefined, md.md_type);
         if (match.TAG === /* Mty_functor */2) {
-          throw {
-                MEL_EXN_ID: $$Error$6,
-                _1: loc,
-                _2: env,
-                _3: {
-                  TAG: /* Access_functor_as_structure */25,
-                  _0: mlid
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$6, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$6,
+                      _1: loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Access_functor_as_structure */25,
+                        _0: mlid
+                      }
+                    }
+                  });
         }
         break;
     case /* Lapply */2 :
         check_module(lid._0);
         check_module(lid._1);
-        throw {
+        throw new Error($$Error$6, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$6,
+                    _1: loc,
+                    _2: env,
+                    _3: {
+                      TAG: /* Ill_typed_functor_application */24,
+                      _0: lid
+                    }
+                  }
+                });
+    
+  }
+  throw new Error($$Error$6, {
+            cause: {
               MEL_EXN_ID: $$Error$6,
               _1: loc,
               _2: env,
-              _3: {
-                TAG: /* Ill_typed_functor_application */24,
-                _0: lid
-              },
-              Error: new Error()
-            };
-    
-  }
-  throw {
-        MEL_EXN_ID: $$Error$6,
-        _1: loc,
-        _2: env,
-        _3: Curry._1(make_error, lid),
-        Error: new Error()
-      };
+              _3: Curry._1(make_error, lid)
+            }
+          });
 }
 
 function find_component(lookup, make_error, env, loc, lid) {
@@ -60044,15 +61307,18 @@ function find_component(lookup, make_error, env, loc, lid) {
       return narrow_unbound_lid_error(env, loc, lid, make_error);
     }
     if (exn.MEL_EXN_ID === Recmodule) {
-      throw {
-            MEL_EXN_ID: $$Error$6,
-            _1: loc,
-            _2: env,
-            _3: /* Illegal_reference_to_recursive_module */1,
-            Error: new Error()
-          };
+      throw new Error($$Error$6, {
+                cause: {
+                  MEL_EXN_ID: $$Error$6,
+                  _1: loc,
+                  _2: env,
+                  _3: /* Illegal_reference_to_recursive_module */1
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -60184,29 +61450,31 @@ function unbound_label_error(env, lid) {
 
 var transl_modtype_longident = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              41489,
-              45
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    41489,
+                    45
+                  ]
+                }
+              });
     })
 };
 
 var transl_modtype = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              41490,
-              35
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    41490,
+                    35
+                  ]
+                }
+              });
     })
 };
 
@@ -60215,16 +61483,17 @@ function create_package_mty(fake, loc, env, param) {
           var s2 = param$1[0];
           var s1 = param[0];
           if (Caml_obj.caml_equal(s1.txt, s2.txt)) {
-            throw {
-                  MEL_EXN_ID: $$Error$6,
-                  _1: loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Multiple_constraints_on_type */15,
-                    _0: s1.txt
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$6, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$6,
+                        _1: loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Multiple_constraints_on_type */15,
+                          _0: s1.txt
+                        }
+                      }
+                    });
           }
           return Caml_obj.caml_compare(s1.txt, s2.txt);
         }), param[1]);
@@ -60337,22 +61606,24 @@ function transl_type_param(env, styp) {
     var ty$1;
     try {
       if (name$1 !== "" && Caml_string.get(name$1, 0) === /* '_' */95) {
-        throw {
-              MEL_EXN_ID: $$Error$6,
-              _1: loc,
-              _2: empty,
-              _3: {
-                TAG: /* Invalid_variable_name */13,
-                _0: "'" + name$1
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$6, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$6,
+                    _1: loc,
+                    _2: empty,
+                    _3: {
+                      TAG: /* Invalid_variable_name */13,
+                      _0: "'" + name$1
+                    }
+                  }
+                });
       }
       find$2(name$1, type_variables.contents);
-      throw {
-            MEL_EXN_ID: Already_bound,
-            Error: new Error()
-          };
+      throw new Error(Already_bound, {
+                cause: {
+                  MEL_EXN_ID: Already_bound
+                }
+              });
     }
     catch (raw_exn){
       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
@@ -60361,7 +61632,9 @@ function transl_type_param(env, styp) {
         type_variables.contents = add$5(name$1, v, type_variables.contents);
         ty$1 = v;
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
     return {
@@ -60375,15 +61648,16 @@ function transl_type_param(env, styp) {
             ctyp_attributes: styp.ptyp_attributes
           };
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          41575,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                41575,
+                9
+              ]
+            }
+          });
 }
 
 function new_pre_univar(name, param) {
@@ -60431,16 +61705,17 @@ function transl_type(env, policy, styp) {
       ty = new_pre_univar(undefined, undefined);
     } else {
       if (policy === /* Fixed */0) {
-        throw {
-              MEL_EXN_ID: $$Error$6,
-              _1: styp.ptyp_loc,
-              _2: env,
-              _3: {
-                TAG: /* Unbound_type_variable */0,
-                _0: "_"
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$6, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$6,
+                    _1: styp.ptyp_loc,
+                    _2: env,
+                    _3: {
+                      TAG: /* Unbound_type_variable */0,
+                      _0: "_"
+                    }
+                  }
+                });
       }
       ty = newvar(validate_name(undefined), undefined);
     }
@@ -60450,16 +61725,17 @@ function transl_type(env, policy, styp) {
     case /* Ptyp_var */0 :
         var name$1 = name._0;
         if (name$1 !== "" && Caml_string.get(name$1, 0) === /* '_' */95) {
-          throw {
-                MEL_EXN_ID: $$Error$6,
-                _1: styp.ptyp_loc,
-                _2: env,
-                _3: {
-                  TAG: /* Invalid_variable_name */13,
-                  _0: "'" + name$1
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$6, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$6,
+                      _1: styp.ptyp_loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Invalid_variable_name */13,
+                        _0: "'" + name$1
+                      }
+                    }
+                  });
         }
         var ty$1;
         try {
@@ -60481,11 +61757,15 @@ function transl_type(env, policy, styp) {
                     ], used_variables.contents);
                 ty$1 = v;
               } else {
-                throw exn$1;
+                throw new Error(exn$1.MEL_EXN_ID, {
+                          cause: exn$1
+                        });
               }
             }
           } else {
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }
         return ctyp({
@@ -60544,18 +61824,19 @@ function transl_type(env, policy, styp) {
           stl$2 = stl$1;
         }
         if (Stdlib__List.length(stl$2) !== decl.type_arity) {
-          throw {
-                MEL_EXN_ID: $$Error$6,
-                _1: styp.ptyp_loc,
-                _2: env,
-                _3: {
-                  TAG: /* Type_arity_mismatch */3,
-                  _0: lid.txt,
-                  _1: decl.type_arity,
-                  _2: Stdlib__List.length(stl$2)
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$6, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$6,
+                      _1: styp.ptyp_loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Type_arity_mismatch */3,
+                        _0: lid.txt,
+                        _1: decl.type_arity,
+                        _2: Stdlib__List.length(stl$2)
+                      }
+                    }
+                  });
         }
         var args = Stdlib__List.map((function (param) {
                 return transl_type(env, policy, param);
@@ -60570,18 +61851,21 @@ function transl_type(env, policy, styp) {
                 catch (raw_exn){
                   var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                   if (exn.MEL_EXN_ID === Unify) {
-                    throw {
-                          MEL_EXN_ID: $$Error$6,
-                          _1: param[0].ptyp_loc,
-                          _2: env,
-                          _3: {
-                            TAG: /* Type_mismatch */6,
-                            _0: swap_list(exn._1)
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$6, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$6,
+                                _1: param[0].ptyp_loc,
+                                _2: env,
+                                _3: {
+                                  TAG: /* Type_mismatch */6,
+                                  _0: swap_list(exn._1)
+                                }
+                              }
+                            });
                   }
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
               }), Stdlib__List.combine(stl$2, args), params);
         var constr = newconstr(path, Stdlib__List.map((function (ctyp) {
@@ -60593,18 +61877,21 @@ function transl_type(env, policy, styp) {
         catch (raw_exn$2){
           var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
           if (exn$2.MEL_EXN_ID === Unify) {
-            throw {
-                  MEL_EXN_ID: $$Error$6,
-                  _1: styp.ptyp_loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Type_mismatch */6,
-                    _0: exn$2._1
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$6, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$6,
+                        _1: styp.ptyp_loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Type_mismatch */6,
+                          _0: exn$2._1
+                        }
+                      }
+                    });
           }
-          throw exn$2;
+          throw new Error(exn$2.MEL_EXN_ID, {
+                    cause: exn$2
+                  });
         }
         return ctyp({
                     TAG: /* Ttyp_constr */3,
@@ -60641,10 +61928,11 @@ function transl_type(env, policy, styp) {
               if (ty !== undefined) {
                 var row = repr(ty).desc;
                 if (typeof row === "number") {
-                  throw {
-                        MEL_EXN_ID: Stdlib.Not_found,
-                        Error: new Error()
-                      };
+                  throw new Error(Stdlib.Not_found, {
+                            cause: {
+                              MEL_EXN_ID: Stdlib.Not_found
+                            }
+                          });
                 }
                 switch (row.TAG | 0) {
                   case /* Tconstr */3 :
@@ -60654,21 +61942,24 @@ function transl_type(env, policy, styp) {
                       if (static_row(row._0)) {
                         return ;
                       }
-                      throw {
-                            MEL_EXN_ID: Stdlib.Not_found,
-                            Error: new Error()
-                          };
+                      throw new Error(Stdlib.Not_found, {
+                                cause: {
+                                  MEL_EXN_ID: Stdlib.Not_found
+                                }
+                              });
                   default:
-                    throw {
-                          MEL_EXN_ID: Stdlib.Not_found,
-                          Error: new Error()
-                        };
+                    throw new Error(Stdlib.Not_found, {
+                              cause: {
+                                MEL_EXN_ID: Stdlib.Not_found
+                              }
+                            });
                 }
               } else {
-                throw {
-                      MEL_EXN_ID: Stdlib.Not_found,
-                      Error: new Error()
-                    };
+                throw new Error(Stdlib.Not_found, {
+                          cause: {
+                            MEL_EXN_ID: Stdlib.Not_found
+                          }
+                        });
               }
             };
           };
@@ -60719,37 +62010,43 @@ function transl_type(env, policy, styp) {
               var exn$4 = Caml_js_exceptions.internalToOCamlException(raw_exn$4);
               if (exn$4.MEL_EXN_ID === Stdlib.Not_found) {
                 find_class$1(env, styp.ptyp_loc, lid$1.txt);
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        41701,
-                        57
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              41701,
+                              57
+                            ]
+                          }
+                        });
               }
-              throw exn$4;
+              throw new Error(exn$4.MEL_EXN_ID, {
+                        cause: exn$4
+                      });
             }
           } else {
-            throw exn$3;
+            throw new Error(exn$3.MEL_EXN_ID, {
+                      cause: exn$3
+                    });
           }
         }
         var decl$2 = match$1[1];
         var path$1 = match$1[0];
         if (Stdlib__List.length(stl$3) !== decl$2.type_arity) {
-          throw {
-                MEL_EXN_ID: $$Error$6,
-                _1: styp.ptyp_loc,
-                _2: env,
-                _3: {
-                  TAG: /* Type_arity_mismatch */3,
-                  _0: lid$1.txt,
-                  _1: decl$2.type_arity,
-                  _2: Stdlib__List.length(stl$3)
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$6, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$6,
+                      _1: styp.ptyp_loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Type_arity_mismatch */3,
+                        _0: lid$1.txt,
+                        _1: decl$2.type_arity,
+                        _2: Stdlib__List.length(stl$3)
+                      }
+                    }
+                  });
         }
         var args$1 = Stdlib__List.map((function (param) {
                 return transl_type(env, policy, param);
@@ -60762,18 +62059,21 @@ function transl_type(env, policy, styp) {
                 catch (raw_exn){
                   var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                   if (exn.MEL_EXN_ID === Unify) {
-                    throw {
-                          MEL_EXN_ID: $$Error$6,
-                          _1: param[0].ptyp_loc,
-                          _2: env,
-                          _3: {
-                            TAG: /* Type_mismatch */6,
-                            _0: swap_list(exn._1)
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$6, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$6,
+                                _1: param[0].ptyp_loc,
+                                _2: env,
+                                _3: {
+                                  TAG: /* Type_mismatch */6,
+                                  _0: swap_list(exn._1)
+                                }
+                              }
+                            });
                   }
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
               }), Stdlib__List.combine(stl$3, args$1), params$1);
         var ty_args = Stdlib__List.map((function (ctyp) {
@@ -60786,31 +62086,35 @@ function transl_type(env, policy, styp) {
         catch (raw_exn$5){
           var exn$5 = Caml_js_exceptions.internalToOCamlException(raw_exn$5);
           if (exn$5.MEL_EXN_ID === Unify) {
-            throw {
-                  MEL_EXN_ID: $$Error$6,
-                  _1: styp.ptyp_loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Type_mismatch */6,
-                    _0: exn$5._1
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$6, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$6,
+                        _1: styp.ptyp_loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Type_mismatch */6,
+                          _0: exn$5._1
+                        }
+                      }
+                    });
           }
-          throw exn$5;
+          throw new Error(exn$5.MEL_EXN_ID, {
+                    cause: exn$5
+                  });
         }
         var row = ty$6.desc;
         var ty$7;
         if (typeof row === "number") {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  41749,
-                  10
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        41749,
+                        10
+                      ]
+                    }
+                  });
         }
         switch (row.TAG | 0) {
           case /* Tobject */4 :
@@ -60896,15 +62200,16 @@ function transl_type(env, policy, styp) {
                   });
               break;
           default:
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    41749,
-                    10
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          41749,
+                          10
+                        ]
+                      }
+                    });
         }
         return ctyp({
                     TAG: /* Ttyp_class */5,
@@ -60926,7 +62231,9 @@ function transl_type(env, policy, styp) {
             if (exn$6.MEL_EXN_ID === Stdlib.Not_found) {
               t$1 = instance(undefined, env, find$2(alias, used_variables.contents)[0]);
             } else {
-              throw exn$6;
+              throw new Error(exn$6.MEL_EXN_ID, {
+                        cause: exn$6
+                      });
             }
           }
           var ty$8 = transl_type(env, policy, st);
@@ -60937,18 +62244,21 @@ function transl_type(env, policy, styp) {
             var exn$7 = Caml_js_exceptions.internalToOCamlException(raw_exn$7);
             if (exn$7.MEL_EXN_ID === Unify) {
               var trace = swap_list(exn$7._1);
-              throw {
-                    MEL_EXN_ID: $$Error$6,
-                    _1: styp.ptyp_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Alias_type_mismatch */7,
-                      _0: trace
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$6, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$6,
+                          _1: styp.ptyp_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Alias_type_mismatch */7,
+                            _0: trace
+                          }
+                        }
+                      });
             }
-            throw exn$7;
+            throw new Error(exn$7.MEL_EXN_ID, {
+                      cause: exn$7
+                    });
           }
           cty = ty$8;
         }
@@ -60971,18 +62281,21 @@ function transl_type(env, policy, styp) {
               var exn$9 = Caml_js_exceptions.internalToOCamlException(raw_exn$9);
               if (exn$9.MEL_EXN_ID === Unify) {
                 var trace$1 = swap_list(exn$9._1);
-                throw {
-                      MEL_EXN_ID: $$Error$6,
-                      _1: styp.ptyp_loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Alias_type_mismatch */7,
-                        _0: trace$1
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$6, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$6,
+                            _1: styp.ptyp_loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Alias_type_mismatch */7,
+                              _0: trace$1
+                            }
+                          }
+                        });
               }
-              throw exn$9;
+              throw new Error(exn$9.MEL_EXN_ID, {
+                        cause: exn$9
+                      });
             }
             if (principal.contents) {
               end_def(undefined);
@@ -61027,7 +62340,9 @@ function transl_type(env, policy, styp) {
               ctyp_attributes: ty$9.ctyp_attributes
             };
           } else {
-            throw exn$8;
+            throw new Error(exn$8.MEL_EXN_ID, {
+                      cause: exn$8
+                    });
           }
         }
         return ctyp({
@@ -61068,17 +62383,18 @@ function transl_type(env, policy, styp) {
             var match = Stdlib__Hashtbl.find(hfields, h);
             var l$p = match[0];
             if (l !== l$p) {
-              throw {
-                    MEL_EXN_ID: $$Error$6,
-                    _1: styp.ptyp_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Variant_tags */12,
-                      _0: l,
-                      _1: l$p
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$6, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$6,
+                          _1: styp.ptyp_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Variant_tags */12,
+                            _0: l,
+                            _1: l$p
+                          }
+                        }
+                      });
             }
             var ty = mkfield(l, f);
             var ty$p = mkfield(l, match[1]);
@@ -61097,19 +62413,22 @@ function transl_type(env, policy, styp) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Unify) {
-                throw {
-                      MEL_EXN_ID: $$Error$6,
-                      _1: loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Constructor_mismatch */10,
-                        _0: ty,
-                        _1: ty$p
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$6, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$6,
+                            _1: loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Constructor_mismatch */10,
+                              _0: ty,
+                              _1: ty$p
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
           catch (raw_exn$1){
@@ -61120,7 +62439,9 @@ function transl_type(env, policy, styp) {
                           f
                         ]);
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
         };
         var add_field = function (param) {
@@ -61152,16 +62473,17 @@ function transl_type(env, policy, styp) {
             }
             if (exit === 1) {
               if (Stdlib__List.length(stl) > 1 || c && Caml_obj.caml_notequal(stl, /* [] */0)) {
-                throw {
-                      MEL_EXN_ID: $$Error$6,
-                      _1: styp.ptyp_loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Present_has_conjunction */8,
-                        _0: l
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$6, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$6,
+                            _1: styp.ptyp_loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Present_has_conjunction */8,
+                              _0: l
+                            }
+                          }
+                        });
               }
               f = tl ? ({
                     TAG: /* Rpresent */0,
@@ -61192,10 +62514,11 @@ function transl_type(env, policy, styp) {
             ];
           try {
             Stdlib__Hashtbl.iter((function (param, param$1) {
-                    throw {
-                          MEL_EXN_ID: Stdlib.Exit,
-                          Error: new Error()
-                        };
+                    throw new Error(Stdlib.Exit, {
+                              cause: {
+                                MEL_EXN_ID: Stdlib.Exit
+                              }
+                            });
                   }), hfields);
             name$2.contents = nm;
           }
@@ -61204,7 +62527,9 @@ function transl_type(env, policy, styp) {
             if (exn.MEL_EXN_ID === Stdlib.Exit) {
               name$2.contents = undefined;
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
           var match$2 = expand_head(env, cty.ctyp_type);
@@ -61217,16 +62542,17 @@ function transl_type(env, policy, styp) {
             switch (row.TAG | 0) {
               case /* Tvar */0 :
                   if (nm !== undefined) {
-                    throw {
-                          MEL_EXN_ID: $$Error$6,
-                          _1: sty.ptyp_loc,
-                          _2: env,
-                          _3: {
-                            TAG: /* Unbound_type_constructor_2 */2,
-                            _0: nm[0]
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$6, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$6,
+                                _1: sty.ptyp_loc,
+                                _2: env,
+                                _3: {
+                                  TAG: /* Unbound_type_constructor_2 */2,
+                                  _0: nm[0]
+                                }
+                              }
+                            });
                   }
                   exit$1 = 1;
                   break;
@@ -61243,16 +62569,17 @@ function transl_type(env, policy, styp) {
             }
           }
           if (exit$1 === 1) {
-            throw {
-                  MEL_EXN_ID: $$Error$6,
-                  _1: sty.ptyp_loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Not_a_variant */11,
-                    _0: ty
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$6, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$6,
+                        _1: sty.ptyp_loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Not_a_variant */11,
+                          _0: ty
+                        }
+                      }
+                    });
           }
           Stdlib__List.iter((function (param) {
                   var f = param[1];
@@ -61260,15 +62587,16 @@ function transl_type(env, policy, styp) {
                   var f$1;
                   if (present !== undefined && !Stdlib__List.mem(l, present)) {
                     if (typeof f === "number") {
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              41862,
-                              24
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    41862,
+                                    24
+                                  ]
+                                }
+                              });
                     }
                     if (f.TAG === /* Rpresent */0) {
                       var ty = f._0;
@@ -61293,15 +62621,16 @@ function transl_type(env, policy, styp) {
                             }
                           });
                     } else {
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              41862,
-                              24
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    41862,
+                                    24
+                                  ]
+                                }
+                              });
                     }
                   } else {
                     f$1 = f;
@@ -61325,16 +62654,17 @@ function transl_type(env, policy, styp) {
                   if (Stdlib__List.mem_assoc(l, fields$2)) {
                     return ;
                   }
-                  throw {
-                        MEL_EXN_ID: $$Error$6,
-                        _1: styp.ptyp_loc,
-                        _2: env,
-                        _3: {
-                          TAG: /* Present_has_no_type */9,
-                          _0: l
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$6, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$6,
+                              _1: styp.ptyp_loc,
+                              _2: env,
+                              _3: {
+                                TAG: /* Present_has_no_type */9,
+                                _0: l
+                              }
+                            }
+                          });
                 }), present);
         }
         var row_row_fields = Stdlib__List.rev(fields$2);
@@ -61411,17 +62741,18 @@ function transl_type(env, policy, styp) {
                           tl: tyl
                         };
                 }
-                throw {
-                      MEL_EXN_ID: $$Error$6,
-                      _1: styp.ptyp_loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Cannot_quantify */14,
-                        _0: param[0],
-                        _1: v
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$6, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$6,
+                            _1: styp.ptyp_loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Cannot_quantify */14,
+                              _0: param[0],
+                              _1: v
+                            }
+                          }
+                        });
               }), /* [] */0, new_univars);
         var ty$p = newty2(100000000, {
               TAG: /* Tpoly */10,
@@ -61475,11 +62806,12 @@ function transl_type(env, policy, styp) {
                     }
                   }, ty$12);
     case /* Ptyp_extension */10 :
-        throw {
-              MEL_EXN_ID: Error_forward,
-              _1: error_of_extension(name._0),
-              Error: new Error()
-            };
+        throw new Error(Error_forward, {
+                  cause: {
+                    MEL_EXN_ID: Error_forward,
+                    _1: error_of_extension(name._0)
+                  }
+                });
     
   }
 }
@@ -61503,16 +62835,17 @@ function transl_fields(loc, env, policy, seen, o, param) {
   var match = param.hd;
   var s = match[0];
   if (Stdlib__List.mem(s, seen)) {
-    throw {
-          MEL_EXN_ID: $$Error$6,
-          _1: loc,
-          _2: env,
-          _3: {
-            TAG: /* Repeated_method_label */16,
-            _0: s
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$6, {
+              cause: {
+                MEL_EXN_ID: $$Error$6,
+                _1: loc,
+                _2: env,
+                _3: {
+                  TAG: /* Repeated_method_label */16,
+                  _0: s
+                }
+              }
+            });
   }
   var ty2 = transl_fields(loc, env, policy, {
         hd: s,
@@ -61609,16 +62942,17 @@ function globalize_used_variables(env, fixed) {
             var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn$1.MEL_EXN_ID === Stdlib.Not_found) {
               if (fixed && is_Tvar(repr(ty))) {
-                throw {
-                      MEL_EXN_ID: $$Error$6,
-                      _1: loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Unbound_type_variable */0,
-                        _0: "'" + name
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$6, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$6,
+                            _1: loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Unbound_type_variable */0,
+                              _0: "'" + name
+                            }
+                          }
+                        });
               }
               var v2 = new_global_var(validate_name(undefined), undefined);
               r.contents = {
@@ -61632,7 +62966,9 @@ function globalize_used_variables(env, fixed) {
               type_variables.contents = add$5(name, v2, type_variables.contents);
               return ;
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
         }), used_variables.contents);
   used_variables.contents = /* Empty */0;
@@ -61644,18 +62980,21 @@ function globalize_used_variables(env, fixed) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Unify) {
-                throw {
-                      MEL_EXN_ID: $$Error$6,
-                      _1: param[0],
-                      _2: env,
-                      _3: {
-                        TAG: /* Type_mismatch */6,
-                        _0: exn._1
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$6, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$6,
+                            _1: param[0],
+                            _2: env,
+                            _3: {
+                              TAG: /* Type_mismatch */6,
+                              _0: exn._1
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }), r.contents);
   };
@@ -62573,57 +63912,61 @@ var Error_forward$1 = /* @__PURE__ */Caml_exceptions.create("Ocaml_typedtree_tes
 
 var type_module = {
   contents: (function (env, md) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              42440,
-              22
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    42440,
+                    22
+                  ]
+                }
+              });
     })
 };
 
 var type_open = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              42446,
-              16
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    42446,
+                    16
+                  ]
+                }
+              });
     })
 };
 
 var type_package = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              42451,
-              16
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    42451,
+                    16
+                  ]
+                }
+              });
     })
 };
 
 var type_object = {
   contents: (function (env, s) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              42455,
-              20
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    42455,
+                    20
+                  ]
+                }
+              });
     })
 };
 
@@ -62979,25 +64322,27 @@ function extract_option_type(env, ty) {
     }
     
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          42638,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                42638,
+                9
+              ]
+            }
+          });
 }
 
 function extract_concrete_record(env, ty) {
   var match = extract_concrete_typedecl(env, ty);
   var match$1 = match[2].type_kind;
   if (typeof match$1 === "number") {
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
   if (match$1.TAG === /* Type_record */0) {
     return [
@@ -63006,10 +64351,11 @@ function extract_concrete_record(env, ty) {
             match$1._0
           ];
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function extract_concrete_variant(env, ty) {
@@ -63025,10 +64371,11 @@ function extract_concrete_variant(env, ty) {
               /* [] */0
             ];
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   } else {
     if (cstrs.TAG !== /* Type_record */0) {
       return [
@@ -63037,10 +64384,11 @@ function extract_concrete_variant(env, ty) {
               cstrs._0
             ];
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   }
 }
 
@@ -63054,17 +64402,20 @@ function extract_label_names(sexp, env, ty) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              42656,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    42656,
+                    4
+                  ]
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -63087,31 +64438,35 @@ function unify_pat_types(loc, env, ty, ty$p) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: $$Error$7,
-            _1: loc,
-            _2: env,
-            _3: {
-              TAG: /* Pattern_type_clash */3,
-              _0: exn._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$7, {
+                cause: {
+                  MEL_EXN_ID: $$Error$7,
+                  _1: loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* Pattern_type_clash */3,
+                    _0: exn._1
+                  }
+                }
+              });
     }
     if (exn.MEL_EXN_ID === Tags) {
-      throw {
-            MEL_EXN_ID: $$Error$6,
-            _1: loc,
-            _2: env,
-            _3: {
-              TAG: /* Variant_tags */12,
-              _0: exn._1,
-              _1: exn._2
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$6, {
+                cause: {
+                  MEL_EXN_ID: $$Error$6,
+                  _1: loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* Variant_tags */12,
+                    _0: exn._1,
+                    _1: exn._2
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -63122,31 +64477,35 @@ function unify_exp_types(loc, env, ty, expected_ty) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: $$Error$7,
-            _1: loc,
-            _2: env,
-            _3: {
-              TAG: /* Expr_type_clash */7,
-              _0: exn._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$7, {
+                cause: {
+                  MEL_EXN_ID: $$Error$7,
+                  _1: loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* Expr_type_clash */7,
+                    _0: exn._1
+                  }
+                }
+              });
     }
     if (exn.MEL_EXN_ID === Tags) {
-      throw {
-            MEL_EXN_ID: $$Error$6,
-            _1: loc,
-            _2: env,
-            _3: {
-              TAG: /* Variant_tags */12,
-              _0: exn._1,
-              _1: exn._2
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$6, {
+                cause: {
+                  MEL_EXN_ID: $$Error$6,
+                  _1: loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* Variant_tags */12,
+                    _0: exn._1,
+                    _1: exn._2
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -63159,15 +64518,16 @@ function get_newtype_level$1(param) {
   if (y !== undefined) {
     return y;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          42694,
-          12
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                42694,
+                12
+              ]
+            }
+          });
 }
 
 function unify_pat_types_gadt(loc, env, ty, ty$p) {
@@ -63176,15 +64536,16 @@ function unify_pat_types_gadt(loc, env, ty, ty$p) {
   if (x !== undefined) {
     newtype_level$2 = x;
   } else {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            42699,
-            14
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  42699,
+                  14
+                ]
+              }
+            });
   }
   try {
     try {
@@ -63200,56 +64561,64 @@ function unify_pat_types_gadt(loc, env, ty, ty$p) {
       var e = Caml_js_exceptions.internalToOCamlException(raw_e);
       Curry._1(TypePairs.clear, unify_eq_set);
       if (e.MEL_EXN_ID === Unify) {
-        throw {
-              MEL_EXN_ID: Unify,
-              _1: e._1,
-              Error: new Error()
-            };
+        throw new Error(Unify, {
+                  cause: {
+                    MEL_EXN_ID: Unify,
+                    _1: e._1
+                  }
+                });
       }
       newtype_level.contents = undefined;
-      throw e;
+      throw new Error(e.MEL_EXN_ID, {
+                cause: e
+              });
     }
   }
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: $$Error$7,
-            _1: loc,
-            _2: env.contents,
-            _3: {
-              TAG: /* Pattern_type_clash */3,
-              _0: exn._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$7, {
+                cause: {
+                  MEL_EXN_ID: $$Error$7,
+                  _1: loc,
+                  _2: env.contents,
+                  _3: {
+                    TAG: /* Pattern_type_clash */3,
+                    _0: exn._1
+                  }
+                }
+              });
     }
     if (exn.MEL_EXN_ID === Tags) {
-      throw {
-            MEL_EXN_ID: $$Error$6,
-            _1: loc,
-            _2: env.contents,
-            _3: {
-              TAG: /* Variant_tags */12,
-              _0: exn._1,
-              _1: exn._2
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$6, {
+                cause: {
+                  MEL_EXN_ID: $$Error$6,
+                  _1: loc,
+                  _2: env.contents,
+                  _3: {
+                    TAG: /* Variant_tags */12,
+                    _0: exn._1,
+                    _1: exn._2
+                  }
+                }
+              });
     }
     if (exn.MEL_EXN_ID === Unification_recursive_abbrev) {
-      throw {
-            MEL_EXN_ID: $$Error$7,
-            _1: loc,
-            _2: env.contents,
-            _3: {
-              TAG: /* Recursive_local_constraint */33,
-              _0: exn._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$7, {
+                cause: {
+                  MEL_EXN_ID: $$Error$7,
+                  _1: loc,
+                  _2: env.contents,
+                  _3: {
+                    TAG: /* Recursive_local_constraint */33,
+                    _0: exn._1
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -63270,30 +64639,32 @@ function finalize_variant(pat) {
   var row = match$1.desc;
   var row$1;
   if (typeof row === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            42725,
-            15
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  42725,
+                  15
+                ]
+              }
+            });
   }
   if (row.TAG === /* Tvariant */8) {
     var row$2 = row._0;
     match._2.contents = row$2;
     row$1 = row_repr_aux(/* [] */0, row$2);
   } else {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            42725,
-            15
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  42725,
+                  15
+                ]
+              }
+            });
   }
   var match$2 = row_field(match._0, row$1);
   if (typeof match$2 === "number") {
@@ -63328,15 +64699,16 @@ function finalize_variant(pat) {
                     tl: match$3.tl
                   });
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              42733,
-              40
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    42733,
+                    40
+                  ]
+                }
+              });
     }
     
   }
@@ -63371,10 +64743,11 @@ function has_variants(p) {
             if (tmp.TAG !== /* Tpat_variant */5) {
               return ;
             }
-            throw {
-                  MEL_EXN_ID: Stdlib.Exit,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Exit, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Exit
+                      }
+                    });
           }), p);
     return false;
   }
@@ -63383,7 +64756,9 @@ function has_variants(p) {
     if (exn.MEL_EXN_ID === Stdlib.Exit) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -63421,16 +64796,17 @@ function enter_variable(is_moduleOpt, is_as_variableOpt, loc, name, ty) {
   if (Stdlib__List.exists((function (param) {
             return param[0].name === name.txt;
           }), pattern_variables.contents)) {
-    throw {
-          MEL_EXN_ID: $$Error$7,
-          _1: loc,
-          _2: empty,
-          _3: {
-            TAG: /* Multiply_bound_variable */5,
-            _0: name.txt
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$7, {
+              cause: {
+                MEL_EXN_ID: $$Error$7,
+                _1: loc,
+                _2: empty,
+                _3: {
+                  TAG: /* Multiply_bound_variable */5,
+                  _0: name.txt
+                }
+              }
+            });
   }
   var id = create(name.txt);
   pattern_variables.contents = {
@@ -63445,13 +64821,14 @@ function enter_variable(is_moduleOpt, is_as_variableOpt, loc, name, ty) {
   };
   if (is_module) {
     if (!allow_modules.contents) {
-      throw {
-            MEL_EXN_ID: $$Error$7,
-            _1: loc,
-            _2: empty,
-            _3: /* Modules_not_allowed */2,
-            Error: new Error()
-          };
+      throw new Error($$Error$7, {
+                cause: {
+                  MEL_EXN_ID: $$Error$7,
+                  _1: loc,
+                  _2: empty,
+                  _3: /* Modules_not_allowed */2
+                }
+              });
     }
     module_variables.contents = {
       hd: [
@@ -63506,19 +64883,22 @@ function enter_orpat_variables(loc, env, p1_vs, p2_vs) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Unify) {
-                throw {
-                      MEL_EXN_ID: $$Error$7,
-                      _1: loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Or_pattern_type_clash */4,
-                        _0: x1,
-                        _1: exn._1
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$7, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$7,
+                            _1: loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Or_pattern_type_clash */4,
+                              _0: x1,
+                              _1: exn._1
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
             return {
                     hd: [
@@ -63529,41 +64909,44 @@ function enter_orpat_variables(loc, env, p1_vs, p2_vs) {
                   };
           }
           var min_var = x1.name < x2.name ? x1 : x2;
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env,
-                _3: {
-                  TAG: /* Orpat_vars */6,
-                  _0: min_var
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Orpat_vars */6,
+                        _0: min_var
+                      }
+                    }
+                  });
         }
-        throw {
-              MEL_EXN_ID: $$Error$7,
-              _1: loc,
-              _2: env,
-              _3: {
-                TAG: /* Orpat_vars */6,
-                _0: x1
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$7, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$7,
+                    _1: loc,
+                    _2: env,
+                    _3: {
+                      TAG: /* Orpat_vars */6,
+                      _0: x1
+                    }
+                  }
+                });
       }
       if (!p2_vs) {
         return /* [] */0;
       }
-      throw {
-            MEL_EXN_ID: $$Error$7,
-            _1: loc,
-            _2: env,
-            _3: {
-              TAG: /* Orpat_vars */6,
-              _0: p2_vs.hd[0]
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$7, {
+                cause: {
+                  MEL_EXN_ID: $$Error$7,
+                  _1: loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* Orpat_vars */6,
+                    _0: p2_vs.hd[0]
+                  }
+                }
+              });
     };
   };
   return unify_vars(p1_vs$1, p2_vs$1);
@@ -63756,16 +65139,17 @@ function build_or_pat(env, loc, lid) {
     }
   }
   if (exit === 1) {
-    throw {
-          MEL_EXN_ID: $$Error$7,
-          _1: loc,
-          _2: env,
-          _3: {
-            TAG: /* Not_a_variant_type */30,
-            _0: lid
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$7, {
+              cause: {
+                MEL_EXN_ID: $$Error$7,
+                _1: loc,
+                _2: env,
+                _3: {
+                  TAG: /* Not_a_variant_type */30,
+                  _0: lid
+                }
+              }
+            });
   }
   var match$1 = Stdlib__List.fold_left((function (param, param$1) {
           var l = param$1[0];
@@ -63929,16 +65313,17 @@ function build_or_pat(env, loc, lid) {
             ty$1
           ];
   }
-  throw {
-        MEL_EXN_ID: $$Error$7,
-        _1: loc,
-        _2: env,
-        _3: {
-          TAG: /* Not_a_variant_type */30,
-          _0: lid
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$7, {
+            cause: {
+              MEL_EXN_ID: $$Error$7,
+              _1: loc,
+              _2: env,
+              _3: {
+                TAG: /* Not_a_variant_type */30,
+                _0: lid
+              }
+            }
+          });
 }
 
 function expand_path(env, _p) {
@@ -63953,7 +65338,9 @@ function expand_path(env, _p) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         decl = undefined;
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
     if (decl !== undefined) {
@@ -63994,27 +65381,34 @@ function wrap_disambiguate(kind, ty, f, x) {
     if (exn.MEL_EXN_ID === $$Error$7) {
       var match = exn._3;
       if (typeof match === "number") {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
       if (match.TAG === /* Wrong_name */13) {
-        throw {
-              MEL_EXN_ID: $$Error$7,
-              _1: exn._1,
-              _2: exn._2,
-              _3: {
-                TAG: /* Wrong_name */13,
-                _0: kind,
-                _1: ty,
-                _2: match._2,
-                _3: match._3,
-                _4: match._4
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$7, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$7,
+                    _1: exn._1,
+                    _2: exn._2,
+                    _3: {
+                      TAG: /* Wrong_name */13,
+                      _0: kind,
+                      _1: ty,
+                      _2: match._2,
+                      _3: match._3,
+                      _4: match._4
+                    }
+                  }
+                });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
 }
@@ -64024,28 +65418,30 @@ var type_kind = "record";
 function get_type_path$1(env, d) {
   var match = d.lbl_res.desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            42965,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  42965,
+                  11
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tconstr */3) {
     return match._0;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          42965,
-          11
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                42965,
+                11
+              ]
+            }
+          });
 }
 
 function lookup_from_type(env, tpath, lid) {
@@ -64063,29 +65459,33 @@ function lookup_from_type(env, tpath, lid) {
         catch (raw_exn){
           var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: lid.loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Wrong_name */13,
-                    _0: "",
-                    _1: newvar(undefined, undefined),
-                    _2: type_kind,
-                    _3: tpath,
-                    _4: lid.txt
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: lid.loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Wrong_name */13,
+                          _0: "",
+                          _1: newvar(undefined, undefined),
+                          _2: type_kind,
+                          _3: tpath,
+                          _4: lid.txt
+                        }
+                      }
+                    });
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Ldot */1 :
     case /* Lapply */2 :
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     
   }
 }
@@ -64226,26 +65626,31 @@ function disambiguate(warnOpt, check_lkOpt, scope, lid, env, opath, lbls) {
                               tp
                             ];
                     }), lbls);
-              throw {
-                    MEL_EXN_ID: $$Error$7,
-                    _1: lid.loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Name_type_mismatch */14,
-                      _0: type_kind,
-                      _1: lid.txt,
-                      _2: tp,
-                      _3: tpl
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$7, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$7,
+                          _1: lid.loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Name_type_mismatch */14,
+                            _0: type_kind,
+                            _1: lid.txt,
+                            _2: tp,
+                            _3: tpl
+                          }
+                        }
+                      });
             }
           } else {
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
         }
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
   } else if (lbls) {
@@ -64495,15 +65900,16 @@ function type_label_a_list(labels, loc, closed, env, type_lbl_a, opath, lid_a_li
                                   ];
                         case /* Ldot */1 :
                         case /* Lapply */2 :
-                            throw {
-                                  MEL_EXN_ID: "Assert_failure",
-                                  _1: [
-                                    "jscomp/test/ocaml_typedtree_test.ml",
-                                    43182,
-                                    17
-                                  ],
-                                  Error: new Error()
-                                };
+                            throw new Error("Assert_failure", {
+                                      cause: {
+                                        MEL_EXN_ID: "Assert_failure",
+                                        _1: [
+                                          "jscomp/test/ocaml_typedtree_test.ml",
+                                          43182,
+                                          17
+                                        ]
+                                      }
+                                    });
                         
                       }
                     }), lid_a_list);
@@ -64564,16 +65970,17 @@ function check_recordpat_labels(loc, lbl_pat_list, closed) {
   var check_defined = function (param) {
     var label = param[1];
     if (Caml_array.get(defined, label.lbl_pos)) {
-      throw {
-            MEL_EXN_ID: $$Error$7,
-            _1: loc,
-            _2: empty,
-            _3: {
-              TAG: /* Label_multiply_defined */10,
-              _0: label.lbl_name
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$7, {
+                cause: {
+                  MEL_EXN_ID: $$Error$7,
+                  _1: loc,
+                  _2: empty,
+                  _3: {
+                    TAG: /* Label_multiply_defined */10,
+                    _0: label.lbl_name
+                  }
+                }
+              });
     }
     Caml_array.set(defined, label.lbl_pos, true);
   };
@@ -64609,28 +66016,30 @@ var type_kind$1 = "variant";
 function get_type_path$2(env, d) {
   var match = d.cstr_res.desc;
   if (typeof match === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            42965,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  42965,
+                  11
+                ]
+              }
+            });
   }
   if (match.TAG === /* Tconstr */3) {
     return match._0;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          42965,
-          11
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                42965,
+                11
+              ]
+            }
+          });
 }
 
 function lookup_from_type$1(env, tpath, lid) {
@@ -64648,29 +66057,33 @@ function lookup_from_type$1(env, tpath, lid) {
         catch (raw_exn){
           var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: lid.loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Wrong_name */13,
-                    _0: "",
-                    _1: newvar(undefined, undefined),
-                    _2: type_kind$1,
-                    _3: tpath,
-                    _4: lid.txt
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: lid.loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Wrong_name */13,
+                          _0: "",
+                          _1: newvar(undefined, undefined),
+                          _2: type_kind$1,
+                          _3: tpath,
+                          _4: lid.txt
+                        }
+                      }
+                    });
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
     case /* Ldot */1 :
     case /* Lapply */2 :
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     
   }
 }
@@ -64811,26 +66224,31 @@ function disambiguate$1(warnOpt, check_lkOpt, scope, lid, env, opath, lbls) {
                               tp
                             ];
                     }), lbls);
-              throw {
-                    MEL_EXN_ID: $$Error$7,
-                    _1: lid.loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Name_type_mismatch */14,
-                      _0: type_kind$1,
-                      _1: lid.txt,
-                      _2: tp,
-                      _3: tpl
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$7, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$7,
+                          _1: lid.loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Name_type_mismatch */14,
+                            _0: type_kind$1,
+                            _1: lid.txt,
+                            _2: tp,
+                            _3: tpl
+                          }
+                        }
+                      });
             }
           } else {
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
         }
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
   } else if (lbls) {
@@ -64869,15 +66287,16 @@ function unify_head_only(loc, env, ty, constr) {
   var ty_res = match[1];
   var match$1 = repr(ty_res).desc;
   if (typeof match$1 === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            43255,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  43255,
+                  9
+                ]
+              }
+            });
   }
   if (match$1.TAG === /* Tconstr */3) {
     ty_res.desc = {
@@ -64891,15 +66310,16 @@ function unify_head_only(loc, env, ty, constr) {
     enforce_constraints(env, ty_res);
     return unify_pat_types(loc, env, ty_res, ty);
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          43255,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                43255,
+                9
+              ]
+            }
+          });
 }
 
 function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty) {
@@ -65012,21 +66432,23 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
             };
             return type_pat$1(undefined, undefined)(p$1, expected_ty);
           }
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env.contents,
-                _3: /* Invalid_interval */5,
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env.contents,
+                      _3: /* Invalid_interval */5
+                    }
+                  });
         }
-        throw {
-              MEL_EXN_ID: $$Error$7,
-              _1: loc,
-              _2: env.contents,
-              _3: /* Invalid_interval */5,
-              Error: new Error()
-            };
+        throw new Error($$Error$7, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$7,
+                    _1: loc,
+                    _2: env.contents,
+                    _3: /* Invalid_interval */5
+                  }
+                });
     case /* Ppat_tuple */4 :
         var spl = name._0;
         if (Stdlib__List.length(spl) < 2) {
@@ -65077,7 +66499,9 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             opath = undefined;
           } else {
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }
         var match$1 = lid.txt;
@@ -65118,17 +66542,18 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
           if (!constr.cstr_generalized) {
             return ;
           }
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: lid.loc,
-                _2: env.contents,
-                _3: {
-                  TAG: /* Unqualified_gadt_pattern */34,
-                  _0: tpath,
-                  _1: constr.cstr_name
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: lid.loc,
+                      _2: env.contents,
+                      _3: {
+                        TAG: /* Unqualified_gadt_pattern */34,
+                        _0: tpath,
+                        _1: constr.cstr_name
+                      }
+                    }
+                  });
         };
         var partial_arg = env.contents;
         var partial_arg$1 = check_lk;
@@ -65138,13 +66563,14 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
         mark_constructor(/* Pattern */1, env.contents, last$1(lid.txt), constr);
         check_deprecated(loc, constr.cstr_attributes, constr.cstr_name);
         if (no_existentials && Caml_obj.caml_notequal(constr.cstr_existentials, /* [] */0)) {
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env.contents,
-                _3: /* Unexpected_existential */4,
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env.contents,
+                      _3: /* Unexpected_existential */4
+                    }
+                  });
         }
         if (constr.cstr_generalized) {
           unify_head_only(loc, env.contents, expected_ty, constr);
@@ -65174,18 +66600,19 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
           sargs = /* [] */0;
         }
         if (Stdlib__List.length(sargs) !== constr.cstr_arity) {
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env.contents,
-                _3: {
-                  TAG: /* Constructor_arity_mismatch */1,
-                  _0: lid.txt,
-                  _1: constr.cstr_arity,
-                  _2: Stdlib__List.length(sargs)
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env.contents,
+                      _3: {
+                        TAG: /* Constructor_arity_mismatch */1,
+                        _0: lid.txt,
+                        _1: constr.cstr_arity,
+                        _2: Stdlib__List.length(sargs)
+                      }
+                    }
+                  });
         }
         var match$2 = instance_constructor([
               env,
@@ -65297,7 +66724,9 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
               newvar(undefined, undefined)
             ];
           } else {
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
         }
         var record_ty = match$3[1];
@@ -65318,19 +66747,22 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$7,
-                    _1: label_lid.loc,
-                    _2: env.contents,
-                    _3: {
-                      TAG: /* Label_mismatch */2,
-                      _0: label_lid.txt,
-                      _1: exn._1
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$7, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$7,
+                          _1: label_lid.loc,
+                          _2: env.contents,
+                          _3: {
+                            TAG: /* Label_mismatch */2,
+                            _0: label_lid.txt,
+                            _1: exn._1
+                          }
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           var arg = type_pat$1(undefined, undefined)(param[2], ty_arg);
           if (Caml_obj.caml_notequal(vars, /* [] */0)) {
@@ -65348,16 +66780,17 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
               }
             };
             if (Stdlib__List.exists(instantiated, vars)) {
-              throw {
-                    MEL_EXN_ID: $$Error$7,
-                    _1: label_lid.loc,
-                    _2: env.contents,
-                    _3: {
-                      TAG: /* Polymorphic_label */0,
-                      _0: label_lid.txt
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$7, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$7,
+                          _1: label_lid.loc,
+                          _2: env.contents,
+                          _3: {
+                            TAG: /* Polymorphic_label */0,
+                            _0: label_lid.txt
+                          }
+                        }
+                      });
             }
             
           }
@@ -65454,15 +66887,16 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
             };
             var match$6 = ty$1.desc;
             if (typeof match$6 === "number") {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      43318,
-                      13
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            43318,
+                            13
+                          ]
+                        }
+                      });
             }
             if (match$6.TAG === /* Tpoly */10) {
               begin_def(undefined);
@@ -65496,15 +66930,16 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
                           pat_attributes: /* [] */0
                         });
             }
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    43318,
-                    13
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          43318,
+                          13
+                        ]
+                      }
+                    });
           }
         }
         if (exit$1 === 1) {
@@ -65642,19 +67077,21 @@ function type_pat(constrs, labels, no_existentials, mode, env, sp, expected_ty)
                     pat_attributes: /* [] */0
                   });
     case /* Ppat_exception */14 :
-        throw {
-              MEL_EXN_ID: $$Error$7,
-              _1: loc,
-              _2: env.contents,
-              _3: /* Exception_pattern_below_toplevel */8,
-              Error: new Error()
-            };
+        throw new Error($$Error$7, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$7,
+                    _1: loc,
+                    _2: env.contents,
+                    _3: /* Exception_pattern_below_toplevel */8
+                  }
+                });
     case /* Ppat_extension */15 :
-        throw {
-              MEL_EXN_ID: Error_forward$1,
-              _1: error_of_extension(name._0),
-              Error: new Error()
-            };
+        throw new Error(Error_forward$1, {
+                  cause: {
+                    MEL_EXN_ID: Error_forward$1,
+                    _1: error_of_extension(name._0)
+                  }
+                });
     
   }
 }
@@ -65673,7 +67110,9 @@ function type_pat$1(allow_existentialsOpt, constrs, labels, levOpt, env, sp, exp
   }
   catch (e){
     newtype_level$1.contents = undefined;
-    throw e;
+    throw new Error(e.MEL_EXN_ID, {
+              cause: e
+            });
   }
 }
 
@@ -66202,10 +67641,11 @@ function approx_type(env, _sty) {
           try {
             var match = lookup_type$1(args._0.txt, env);
             if (Stdlib__List.length(ctl) !== match[1].type_arity) {
-              throw {
-                    MEL_EXN_ID: Stdlib.Not_found,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Not_found, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Not_found
+                        }
+                      });
             }
             var tyl = Stdlib__List.map((function (param) {
                     return approx_type(env, param);
@@ -66217,7 +67657,9 @@ function approx_type(env, _sty) {
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
               return newvar(undefined, undefined);
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
       case /* Ptyp_poly */8 :
           _sty = args._1;
@@ -66306,18 +67748,21 @@ function type_approx(env, _sexp) {
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$7,
-                    _1: sexp.pexp_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Expr_type_clash */7,
-                      _0: exn._1
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$7, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$7,
+                          _1: sexp.pexp_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Expr_type_clash */7,
+                            _0: exn._1
+                          }
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           return ty1;
       case /* Pexp_coerce */20 :
@@ -66337,18 +67782,21 @@ function type_approx(env, _sexp) {
           catch (raw_exn$1){
             var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
             if (exn$1.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$7,
-                    _1: sexp.pexp_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Expr_type_clash */7,
-                      _0: exn$1._1
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$7, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$7,
+                          _1: sexp.pexp_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Expr_type_clash */7,
+                            _0: exn$1._1
+                          }
+                        }
+                      });
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
           return ty2;
       default:
@@ -66436,29 +67884,30 @@ function check_univars(env, expans, kind, exp, ty_expected, vars) {
         _1: vars$p
       });
   var ty_expected$1 = repr(ty_expected);
-  throw {
-        MEL_EXN_ID: $$Error$7,
-        _1: exp.exp_loc,
-        _2: env,
-        _3: {
-          TAG: /* Less_general */31,
-          _0: kind,
-          _1: {
-            hd: [
-              ty,
-              ty
-            ],
-            tl: {
-              hd: [
-                ty_expected$1,
-                ty_expected$1
-              ],
-              tl: /* [] */0
+  throw new Error($$Error$7, {
+            cause: {
+              MEL_EXN_ID: $$Error$7,
+              _1: exp.exp_loc,
+              _2: env,
+              _3: {
+                TAG: /* Less_general */31,
+                _0: kind,
+                _1: {
+                  hd: [
+                    ty,
+                    ty
+                  ],
+                  tl: {
+                    hd: [
+                      ty_expected$1,
+                      ty_expected$1
+                    ],
+                    tl: /* [] */0
+                  }
+                }
+              }
             }
-          }
-        },
-        Error: new Error()
-      };
+          });
 }
 
 function check_application_result(env, statement, exp) {
@@ -66492,10 +67941,11 @@ function generalizable(level, ty) {
       return ;
     }
     if (ty$1.level <= level) {
-      throw {
-            MEL_EXN_ID: Stdlib.Exit,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Exit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Exit
+                }
+              });
     }
     mark_type_node(ty$1);
     iter_type_expr(check, ty$1);
@@ -66511,7 +67961,9 @@ function generalizable(level, ty) {
       unmark_type(ty);
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -66556,10 +68008,11 @@ function contains_variant_either(ty) {
               if (match.TAG === /* Rpresent */0) {
                 return ;
               }
-              throw {
-                    MEL_EXN_ID: Stdlib.Exit,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Exit, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Exit
+                        }
+                      });
             }), row$1.row_fields);
     }
     iter_row(loop, row$1);
@@ -66575,7 +68028,9 @@ function contains_variant_either(ty) {
       unmark_type(ty);
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -66617,10 +68072,11 @@ function contains_polymorphic_variant(p) {
     switch (match.TAG | 0) {
       case /* Ppat_variant */6 :
       case /* Ppat_type */11 :
-          throw {
-                MEL_EXN_ID: Stdlib.Exit,
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Exit, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Exit
+                    }
+                  });
       default:
         return iter_ppat(loop, p);
     }
@@ -66634,7 +68090,9 @@ function contains_polymorphic_variant(p) {
     if (exn.MEL_EXN_ID === Stdlib.Exit) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -66653,16 +68111,19 @@ function contains_gadt(env, p) {
               if (!param[0].cstr_generalized) {
                 return ;
               }
-              throw {
-                    MEL_EXN_ID: Stdlib.Exit,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Exit, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Exit
+                        }
+                      });
             }), cstrs);
     }
     catch (raw_exn){
       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
       if (exn.MEL_EXN_ID !== Stdlib.Not_found) {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
       
     }
@@ -66677,7 +68138,9 @@ function contains_gadt(env, p) {
     if (exn.MEL_EXN_ID === Stdlib.Exit) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -66783,7 +68246,9 @@ function duplicate_ident_types(loc, caselist, env) {
                   if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                     return env;
                   }
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
               }), env, idents);
 }
@@ -66843,16 +68308,17 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         var tmp;
         if (typeof match$1 === "number") {
           if (match$1 === /* Val_unbound */1) {
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Masked_instance_variable */29,
-                    _0: lid$1.txt
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Masked_instance_variable */29,
+                          _0: lid$1.txt
+                        }
+                      }
+                    });
           }
           tmp = {
             TAG: /* Texp_ident */0,
@@ -66878,15 +68344,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                       break;
                   case /* Ldot */1 :
                   case /* Lapply */2 :
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              44136,
-                              38
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    44136,
+                                    38
+                                  ]
+                                }
+                              });
                   
                 }
                 tmp = {
@@ -67067,15 +68534,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         var l = lid._0;
         if ($$default !== undefined) {
           if (!is_optional(l)) {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    44215,
-                    6
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          44215,
+                          6
+                        ]
+                      }
+                    });
           }
           var default_loc = $$default.pexp_loc;
           var scases_0 = Curry._3(Ast_helper_Exp.$$case, construct(default_loc, undefined, {
@@ -67192,17 +68660,20 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                   catch (raw_exn){
                     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                     if (exn.MEL_EXN_ID === Unify) {
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              44266,
-                              65
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    44266,
+                                    65
+                                  ]
+                                }
+                              });
                     }
-                    throw exn;
+                    throw new Error(exn.MEL_EXN_ID, {
+                              cause: exn
+                            });
                   }
                   _ty_fun = match._2;
                   _seen = {
@@ -67276,13 +68747,14 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         var exn_caselist = match$10[1];
         var val_caselist = match$10[0];
         if (Caml_obj.caml_equal(val_caselist, /* [] */0) && Caml_obj.caml_notequal(exn_caselist, /* [] */0)) {
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env,
-                _3: /* No_value_clauses */7,
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env,
+                      _3: /* No_value_clauses */7
+                    }
+                  });
         }
         var match$11 = type_cases(undefined, env, arg.exp_type, ty_expected, true, loc, val_caselist);
         var match$12 = type_cases(undefined, env, type_exn, ty_expected, false, loc, exn_caselist);
@@ -67369,7 +68841,9 @@ function type_expect_(in_function, env, sexp, ty_expected) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             opath = undefined;
           } else {
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }
         var constrs = find_all_constructors(env, lid$2.loc, lid$2.txt);
@@ -67389,18 +68863,19 @@ function type_expect_(in_function, env, sexp, ty_expected) {
           sargs$1 = /* [] */0;
         }
         if (Stdlib__List.length(sargs$1) !== constr.cstr_arity) {
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env,
-                _3: {
-                  TAG: /* Constructor_arity_mismatch */1,
-                  _0: lid$2.txt,
-                  _1: constr.cstr_arity,
-                  _2: Stdlib__List.length(sargs$1)
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Constructor_arity_mismatch */1,
+                        _0: lid$2.txt,
+                        _1: constr.cstr_arity,
+                        _2: Stdlib__List.length(sargs$1)
+                      }
+                    }
+                  });
         }
         var separate = principal.contents || env.local_constraints;
         if (separate) {
@@ -67449,15 +68924,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
             match$16.hd
           ];
         } else {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  45498,
-                  11
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        45498,
+                        11
+                      ]
+                    }
+                  });
         }
         var ty_res$1 = match$17[1];
         var texp_exp_desc = texp.exp_desc;
@@ -67480,16 +68956,17 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                 return type_argument(env, e, param[0], param[1]);
               }), sargs$1, Stdlib__List.combine(ty_args, match$17[0]));
         if (constr.cstr_private === /* Private */0) {
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env,
-                _3: {
-                  TAG: /* Private_type */19,
-                  _0: ty_res$1
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Private_type */19,
+                        _0: ty_res$1
+                      }
+                    }
+                  });
         }
         return {
                 exp_desc: {
@@ -67514,37 +68991,41 @@ function type_expect_(in_function, env, sexp, ty_expected) {
           if (sarg$1 !== undefined) {
             var row = match$18.desc;
             if (typeof row === "number") {
-              throw {
-                    MEL_EXN_ID: Stdlib.Not_found,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Not_found, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Not_found
+                        }
+                      });
             }
             if (row.TAG === /* Tvariant */8) {
               var row0 = match$19.desc;
               if (typeof row0 === "number") {
-                throw {
-                      MEL_EXN_ID: Stdlib.Not_found,
-                      Error: new Error()
-                    };
+                throw new Error(Stdlib.Not_found, {
+                          cause: {
+                            MEL_EXN_ID: Stdlib.Not_found
+                          }
+                        });
               }
               if (row0.TAG === /* Tvariant */8) {
                 var row$1 = row_repr_aux(/* [] */0, row._0);
                 var match$20 = row_field_repr_aux(/* [] */0, Stdlib__List.assoc(l$1, row$1.row_fields));
                 var match$21 = row_field_repr_aux(/* [] */0, Stdlib__List.assoc(l$1, row0._0.row_fields));
                 if (typeof match$20 === "number") {
-                  throw {
-                        MEL_EXN_ID: Stdlib.Not_found,
-                        Error: new Error()
-                      };
+                  throw new Error(Stdlib.Not_found, {
+                            cause: {
+                              MEL_EXN_ID: Stdlib.Not_found
+                            }
+                          });
                 }
                 if (match$20.TAG === /* Rpresent */0) {
                   var ty$1 = match$20._0;
                   if (ty$1 !== undefined) {
                     if (typeof match$21 === "number") {
-                      throw {
-                            MEL_EXN_ID: Stdlib.Not_found,
-                            Error: new Error()
-                          };
+                      throw new Error(Stdlib.Not_found, {
+                                cause: {
+                                  MEL_EXN_ID: Stdlib.Not_found
+                                }
+                              });
                     }
                     if (match$21.TAG === /* Rpresent */0) {
                       var ty0 = match$21._0;
@@ -67563,44 +69044,51 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                                     exp_attributes: sexp.pexp_attributes
                                   });
                       }
-                      throw {
-                            MEL_EXN_ID: Stdlib.Not_found,
-                            Error: new Error()
-                          };
+                      throw new Error(Stdlib.Not_found, {
+                                cause: {
+                                  MEL_EXN_ID: Stdlib.Not_found
+                                }
+                              });
                     }
-                    throw {
-                          MEL_EXN_ID: Stdlib.Not_found,
-                          Error: new Error()
-                        };
+                    throw new Error(Stdlib.Not_found, {
+                              cause: {
+                                MEL_EXN_ID: Stdlib.Not_found
+                              }
+                            });
                   } else {
-                    throw {
-                          MEL_EXN_ID: Stdlib.Not_found,
-                          Error: new Error()
-                        };
+                    throw new Error(Stdlib.Not_found, {
+                              cause: {
+                                MEL_EXN_ID: Stdlib.Not_found
+                              }
+                            });
                   }
                 } else {
-                  throw {
-                        MEL_EXN_ID: Stdlib.Not_found,
-                        Error: new Error()
-                      };
+                  throw new Error(Stdlib.Not_found, {
+                            cause: {
+                              MEL_EXN_ID: Stdlib.Not_found
+                            }
+                          });
                 }
               } else {
-                throw {
-                      MEL_EXN_ID: Stdlib.Not_found,
-                      Error: new Error()
-                    };
+                throw new Error(Stdlib.Not_found, {
+                          cause: {
+                            MEL_EXN_ID: Stdlib.Not_found
+                          }
+                        });
               }
             } else {
-              throw {
-                    MEL_EXN_ID: Stdlib.Not_found,
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib.Not_found, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib.Not_found
+                        }
+                      });
             }
           } else {
-            throw {
-                  MEL_EXN_ID: Stdlib.Not_found,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Not_found, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Not_found
+                      }
+                    });
           }
         }
         catch (raw_exn$1){
@@ -67645,7 +69133,9 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                         exp_attributes: sexp.pexp_attributes
                       });
           }
-          throw exn$1;
+          throw new Error(exn$1.MEL_EXN_ID, {
+                    cause: exn$1
+                  });
         }
     case /* Pexp_record */11 :
         var opt_sexp = lid._1;
@@ -67681,7 +69171,9 @@ function type_expect_(in_function, env, sexp, ty_expected) {
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
               return ;
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         };
         var op = get_path(ty_expected);
@@ -67735,16 +69227,17 @@ function type_expect_(in_function, env, sexp, ty_expected) {
             if (match) {
               var lbl1 = param.hd[1];
               if (lbl1.lbl_pos === match.hd[1].lbl_pos) {
-                throw {
-                      MEL_EXN_ID: $$Error$7,
-                      _1: loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Label_multiply_defined */10,
-                        _0: lbl1.lbl_name
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$7, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$7,
+                            _1: loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Label_multiply_defined */10,
+                              _0: lbl1.lbl_name
+                            }
+                          }
+                        });
               }
               _param = param.tl;
               continue ;
@@ -67780,15 +69273,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
               exp_attributes: opt_exp.exp_attributes
             };
           } else {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    44455,
-                    15
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          44455,
+                          15
+                        ]
+                      }
+                    });
           }
         } else {
           opt_exp$1 = undefined;
@@ -67797,15 +69291,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         if (lbl_exp_list) {
           num_fields = lbl_exp_list.hd[1].lbl_all.length;
         } else {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  44458,
-                  38
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        44458,
+                        38
+                      ]
+                    }
+                  });
         }
         if (opt_sexp === undefined && Stdlib__List.length(lid_sexp_list) !== num_fields) {
           var present_indices = Stdlib__List.map((function (param) {
@@ -67832,16 +69327,17 @@ function type_expect_(in_function, env, sexp, ty_expected) {
             };
           };
           var missing = missing_labels(0, label_names);
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env,
-                _3: {
-                  TAG: /* Label_missing */11,
-                  _0: missing
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Label_missing */11,
+                        _0: missing
+                      }
+                    }
+                  });
         }
         if (opt_sexp !== undefined && Stdlib__List.length(lid_sexp_list) === num_fields) {
           prerr_warning(loc, /* Useless_record_with */11);
@@ -67891,16 +69387,17 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         var label$1 = match$26[1];
         unify_exp(env, record$4, ty_record$1);
         if (label$1.lbl_mut === /* Immutable */0) {
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env,
-                _3: {
-                  TAG: /* Label_not_mutable */12,
-                  _0: lid$4.txt
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Label_not_mutable */12,
+                        _0: lid$4.txt
+                      }
+                    }
+                  });
         }
         return rue({
                     exp_desc: {
@@ -68027,13 +69524,14 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                 val_attributes: /* [] */0
               }, env);
         } else {
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: param.ppat_loc,
-                _2: env,
-                _3: /* Invalid_for_loop_index */6,
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: param.ppat_loc,
+                      _2: env,
+                      _3: /* Invalid_for_loop_index */6
+                    }
+                  });
         }
         var body$3 = type_statement(match$28[1], lid._4);
         return rue({
@@ -68100,19 +69598,22 @@ function type_expect_(in_function, env, sexp, ty_expected) {
           catch (raw_exn$2){
             var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
             if (exn$2.MEL_EXN_ID === Subtype) {
-              throw {
-                    MEL_EXN_ID: $$Error$7,
-                    _1: loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Not_subtype */23,
-                      _0: exn$2._1,
-                      _1: exn$2._2
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$7, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$7,
+                          _1: loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Not_subtype */23,
+                            _0: exn$2._1,
+                            _1: exn$2._2
+                          }
+                        }
+                      });
             }
-            throw exn$2;
+            throw new Error(exn$2.MEL_EXN_ID, {
+                      cause: exn$2
+                    });
           }
           end_def(undefined);
           generalize_structure$1(current_level.contents, ty$5);
@@ -68176,7 +69677,9 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                     backtrack(snap);
                     tmp$4 = false;
                   } else {
-                    throw exn$3;
+                    throw new Error(exn$3.MEL_EXN_ID, {
+                              cause: exn$3
+                            });
                   }
                 }
                 tmp$3 = tmp$4;
@@ -68197,19 +69700,22 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                 catch (raw_exn$4){
                   var exn$4 = Caml_js_exceptions.internalToOCamlException(raw_exn$4);
                   if (exn$4.MEL_EXN_ID === Subtype) {
-                    throw {
-                          MEL_EXN_ID: $$Error$7,
-                          _1: loc,
-                          _2: env,
-                          _3: {
-                            TAG: /* Not_subtype */23,
-                            _0: exn$4._1,
-                            _1: exn$4._2
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$7, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$7,
+                                _1: loc,
+                                _2: env,
+                                _3: {
+                                  TAG: /* Not_subtype */23,
+                                  _0: exn$4._1,
+                                  _1: exn$4._2
+                                }
+                              }
+                            });
                   }
-                  throw exn$4;
+                  throw new Error(exn$4.MEL_EXN_ID, {
+                            cause: exn$4
+                          });
                 }
               }
               
@@ -68222,21 +69728,24 @@ function type_expect_(in_function, env, sexp, ty_expected) {
               catch (raw_exn$5){
                 var exn$5 = Caml_js_exceptions.internalToOCamlException(raw_exn$5);
                 if (exn$5.MEL_EXN_ID === Unify) {
-                  throw {
-                        MEL_EXN_ID: $$Error$7,
-                        _1: sarg$2.pexp_loc,
-                        _2: env,
-                        _3: {
-                          TAG: /* Coercion_failure */25,
-                          _0: ty$p$2,
-                          _1: full_expand(env, ty$p$2),
-                          _2: exn$5._1,
-                          _3: match$38[1]
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$7, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$7,
+                              _1: sarg$2.pexp_loc,
+                              _2: env,
+                              _3: {
+                                TAG: /* Coercion_failure */25,
+                                _0: ty$p$2,
+                                _1: full_expand(env, ty$p$2),
+                                _2: exn$5._1,
+                                _3: match$38[1]
+                              }
+                            }
+                          });
                 }
-                throw exn$5;
+                throw new Error(exn$5.MEL_EXN_ID, {
+                          cause: exn$5
+                        });
               }
             }
           }
@@ -68312,18 +69821,21 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                     catch (raw_exn$6){
                       var exn$6 = Caml_js_exceptions.internalToOCamlException(raw_exn$6);
                       if (exn$6.MEL_EXN_ID === Stdlib.Not_found) {
-                        throw {
-                              MEL_EXN_ID: $$Error$7,
-                              _1: e.pexp_loc,
-                              _2: env,
-                              _3: {
-                                TAG: /* Undefined_inherited_method */17,
-                                _0: met
-                              },
-                              Error: new Error()
-                            };
+                        throw new Error($$Error$7, {
+                                  cause: {
+                                    MEL_EXN_ID: $$Error$7,
+                                    _1: e.pexp_loc,
+                                    _2: env,
+                                    _3: {
+                                      TAG: /* Undefined_inherited_method */17,
+                                      _0: met
+                                    }
+                                  }
+                                });
                       }
-                      throw exn$6;
+                      throw new Error(exn$6.MEL_EXN_ID, {
+                                cause: exn$6
+                              });
                     }
                     var match$43 = lookup_value$1({
                           TAG: /* Lident */0,
@@ -68336,15 +69848,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                     var desc$3 = match$43[1];
                     var match$45 = desc$3.val_kind;
                     if (typeof match$45 === "number") {
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              44747,
-                              18
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    44747,
+                                    18
+                                  ]
+                                }
+                              });
                     }
                     if (match$45.TAG === /* Val_self */2) {
                       var match$46 = filter_self_method(env, met, /* Private */0, match$45._0, match$45._3);
@@ -68415,15 +69928,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                         typ$1
                       ];
                     } else {
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              44747,
-                              18
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    44747,
+                                    18
+                                  ]
+                                }
+                              });
                     }
                     break;
                 default:
@@ -68452,15 +69966,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
           var match$48 = ty$6.desc;
           var typ$3;
           if (typeof match$48 === "number") {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    44773,
-                    14
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          44773,
+                          14
+                        ]
+                      }
+                    });
           }
           switch (match$48.TAG | 0) {
             case /* Tvar */0 :
@@ -68488,15 +70003,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                 }
                 break;
             default:
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      44773,
-                      14
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            44773,
+                            14
+                          ]
+                        }
+                      });
           }
           return rue({
                       exp_desc: {
@@ -68515,19 +70031,22 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         catch (raw_exn$7){
           var exn$7 = Caml_js_exceptions.internalToOCamlException(raw_exn$7);
           if (exn$7.MEL_EXN_ID === Unify) {
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: e.pexp_loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Undefined_method */16,
-                    _0: obj.exp_type,
-                    _1: met
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: e.pexp_loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Undefined_method */16,
+                          _0: obj.exp_type,
+                          _1: met
+                        }
+                      }
+                    });
           }
-          throw exn$7;
+          throw new Error(exn$7.MEL_EXN_ID, {
+                    cause: exn$7
+                  });
         }
         break;
     case /* Pexp_new */22 :
@@ -68550,16 +70069,17 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                       exp_attributes: sexp.pexp_attributes
                     });
         }
-        throw {
-              MEL_EXN_ID: $$Error$7,
-              _1: loc,
-              _2: env,
-              _3: {
-                TAG: /* Virtual_class */18,
-                _0: cl.txt
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$7, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$7,
+                    _1: loc,
+                    _2: env,
+                    _3: {
+                      TAG: /* Virtual_class */18,
+                      _0: cl.txt
+                    }
+                  }
+                });
     case /* Pexp_setinstvar */23 :
         var lab = lid._0;
         try {
@@ -68595,50 +70115,55 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                             exp_attributes: sexp.pexp_attributes
                           });
               }
-              throw {
-                    MEL_EXN_ID: $$Error$7,
-                    _1: loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Instance_variable_not_mutable */22,
-                      _0: true,
-                      _1: lab.txt
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$7, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$7,
+                          _1: loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Instance_variable_not_mutable */22,
+                            _0: true,
+                            _1: lab.txt
+                          }
+                        }
+                      });
             }
             exit$4 = 1;
           }
           if (exit$4 === 1) {
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Instance_variable_not_mutable */22,
-                    _0: false,
-                    _1: lab.txt
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Instance_variable_not_mutable */22,
+                          _0: false,
+                          _1: lab.txt
+                        }
+                      }
+                    });
           }
           
         }
         catch (raw_exn$8){
           var exn$8 = Caml_js_exceptions.internalToOCamlException(raw_exn$8);
           if (exn$8.MEL_EXN_ID === Stdlib.Not_found) {
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Unbound_instance_variable */21,
-                    _0: lab.txt
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Unbound_instance_variable */21,
+                          _0: lab.txt
+                        }
+                      }
+                    });
           }
-          throw exn$8;
+          throw new Error(exn$8.MEL_EXN_ID, {
+                    cause: exn$8
+                  });
         }
         break;
     case /* Pexp_override */24 :
@@ -68648,16 +70173,17 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                 if (Stdlib__List.exists((function (l) {
                           return l.txt === lab.txt;
                         }), l)) {
-                  throw {
-                        MEL_EXN_ID: $$Error$7,
-                        _1: loc,
-                        _2: env,
-                        _3: {
-                          TAG: /* Value_multiply_overridden */24,
-                          _0: lab.txt
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$7, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$7,
+                              _1: loc,
+                              _2: env,
+                              _3: {
+                                TAG: /* Value_multiply_overridden */24,
+                                _0: lab.txt
+                              }
+                            }
+                          });
                 }
                 return {
                         hd: lab,
@@ -68680,28 +70206,32 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         catch (raw_exn$9){
           var exn$9 = Caml_js_exceptions.internalToOCamlException(raw_exn$9);
           if (exn$9.MEL_EXN_ID === Stdlib.Not_found) {
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: loc,
-                  _2: env,
-                  _3: /* Outside_class */0,
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: loc,
+                        _2: env,
+                        _3: /* Outside_class */0
+                      }
+                    });
           }
-          throw exn$9;
+          throw new Error(exn$9.MEL_EXN_ID, {
+                    cause: exn$9
+                  });
         }
         var match$54 = match$53[0][1];
         var match$55 = match$54.val_kind;
         if (typeof match$55 === "number") {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  44857,
-                  10
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        44857,
+                        10
+                      ]
+                    }
+                  });
         }
         if (match$55.TAG === /* Val_self */2) {
           var vars = match$55._1;
@@ -68721,18 +70251,21 @@ function type_expect_(in_function, env, sexp, ty_expected) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-                throw {
-                      MEL_EXN_ID: $$Error$7,
-                      _1: loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Unbound_instance_variable */21,
-                        _0: lab.txt
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$7, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$7,
+                            _1: loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Unbound_instance_variable */21,
+                              _0: lab.txt
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           };
           var modifs = Stdlib__List.map(type_override, lst);
@@ -68749,15 +70282,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                       exp_attributes: sexp.pexp_attributes
                     });
         }
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                44857,
-                10
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      44857,
+                      10
+                    ]
+                  }
+                });
     case /* Pexp_letmodule */25 :
         var name$2 = lid._0;
         var ty$9 = newvar(undefined, undefined);
@@ -68777,19 +70311,22 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         catch (raw_exn$10){
           var exn$10 = Caml_js_exceptions.internalToOCamlException(raw_exn$10);
           if (exn$10.MEL_EXN_ID === Unify) {
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Scoping_let_module */28,
-                    _0: name$2.txt,
-                    _1: body$4.exp_type
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Scoping_let_module */28,
+                          _0: name$2.txt,
+                          _1: body$4.exp_type
+                        }
+                      }
+                    });
           }
-          throw exn$10;
+          throw new Error(exn$10.MEL_EXN_ID, {
+                    cause: exn$10
+                  });
         }
         return re({
                     exp_desc: {
@@ -68871,15 +70408,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         var match$59 = expand_head(env, ty$11).desc;
         var exp$2;
         if (typeof match$59 === "number") {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  44963,
-                  15
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        44963,
+                        15
+                      ]
+                    }
+                  });
         }
         switch (match$59.TAG | 0) {
           case /* Tvar */0 :
@@ -68942,15 +70480,16 @@ function type_expect_(in_function, env, sexp, ty_expected) {
               }
               break;
           default:
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    44963,
-                    15
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          44963,
+                          15
+                        ]
+                      }
+                    });
         }
         return re({
                     exp_desc: exp$2.exp_desc,
@@ -69062,26 +70601,28 @@ function type_expect_(in_function, env, sexp, ty_expected) {
         var match$64 = match$63.desc;
         var match$65;
         if (typeof match$64 === "number") {
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env,
-                _3: {
-                  TAG: /* Not_a_packed_module */32,
-                  _0: ty_expected
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Not_a_packed_module */32,
+                        _0: ty_expected
+                      }
+                    }
+                  });
         }
         switch (match$64.TAG | 0) {
           case /* Tvar */0 :
-              throw {
-                    MEL_EXN_ID: $$Error$7,
-                    _1: loc,
-                    _2: env,
-                    _3: /* Cannot_infer_signature */3,
-                    Error: new Error()
-                  };
+              throw new Error($$Error$7, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$7,
+                          _1: loc,
+                          _2: env,
+                          _3: /* Cannot_infer_signature */3
+                        }
+                      });
           case /* Tpackage */11 :
               if (principal.contents && expand_head(env, ty_expected).level < 100000000) {
                 prerr_warning(loc, {
@@ -69096,16 +70637,17 @@ function type_expect_(in_function, env, sexp, ty_expected) {
               ];
               break;
           default:
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Not_a_packed_module */32,
-                    _0: ty_expected
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Not_a_packed_module */32,
+                          _0: ty_expected
+                        }
+                      }
+                    });
         }
         var nl = match$65[1];
         var p = match$65[0];
@@ -69154,11 +70696,12 @@ function type_expect_(in_function, env, sexp, ty_expected) {
                 exp_attributes: exp$7.exp_attributes
               };
     case /* Pexp_extension */33 :
-        throw {
-              MEL_EXN_ID: Error_forward$1,
-              _1: error_of_extension(lid._0),
-              Error: new Error()
-            };
+        throw new Error(Error_forward$1, {
+                  cause: {
+                    MEL_EXN_ID: Error_forward$1,
+                    _1: error_of_extension(lid._0)
+                  }
+                });
     
   }
 }
@@ -69188,36 +70731,40 @@ function type_function(in_function, loc, attrs, env, ty_expected, l, caselist) {
         exit = 1;
       } else {
         if (match$2.TAG === /* Tarrow */1) {
-          throw {
-                MEL_EXN_ID: $$Error$7,
-                _1: loc,
-                _2: env,
-                _3: {
-                  TAG: /* Abstract_wrong_label */27,
-                  _0: l,
-                  _1: ty
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$7, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$7,
+                      _1: loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Abstract_wrong_label */27,
+                        _0: l,
+                        _1: ty
+                      }
+                    }
+                  });
         }
         exit = 1;
       }
       if (exit === 1) {
-        throw {
-              MEL_EXN_ID: $$Error$7,
-              _1: loc_fun,
-              _2: env,
-              _3: {
-                TAG: /* Too_many_arguments */26,
-                _0: in_function !== undefined,
-                _1: ty_fun
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$7, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$7,
+                    _1: loc_fun,
+                    _2: env,
+                    _3: {
+                      TAG: /* Too_many_arguments */26,
+                      _0: in_function !== undefined,
+                      _1: ty_fun
+                    }
+                  }
+                });
       }
       
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   var ty_res = match$1[1];
@@ -69231,17 +70778,20 @@ function type_function(in_function, loc, attrs, env, ty_expected, l, caselist) {
     catch (raw_exn$1){
       var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
       if (exn$1.MEL_EXN_ID === Unify) {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                45069,
-                24
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      45069,
+                      24
+                    ]
+                  }
+                });
       }
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
     ty_arg$1 = type_option$1(tv);
   } else {
@@ -69313,7 +70863,9 @@ function type_label_access(env, loc, srecord, lid) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       opath = undefined;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   var labels = find_all_labels(env, lid.loc, lid.txt);
@@ -69328,15 +70880,16 @@ function type_label_access(env, loc, srecord, lid) {
 }
 
 function type_format(loc, str, env) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          45122,
-          1
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                45122,
+                1
+              ]
+            }
+          });
 }
 
 function type_label_exp(create, env, loc, ty_expected, param) {
@@ -69364,19 +70917,22 @@ function type_label_exp(create, env, loc, ty_expected, param) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: $$Error$7,
-            _1: lid.loc,
-            _2: env,
-            _3: {
-              TAG: /* Label_mismatch */2,
-              _0: lid.txt,
-              _1: exn._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$7, {
+                cause: {
+                  MEL_EXN_ID: $$Error$7,
+                  _1: lid.loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* Label_mismatch */2,
+                    _0: lid.txt,
+                    _1: exn._1
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   var ty_arg$1 = instance_def(ty_arg);
   if (separate) {
@@ -69385,28 +70941,30 @@ function type_label_exp(create, env, loc, ty_expected, param) {
   }
   if (label.lbl_private === /* Private */0) {
     if (create) {
-      throw {
-            MEL_EXN_ID: $$Error$7,
-            _1: loc,
-            _2: env,
-            _3: {
-              TAG: /* Private_type */19,
-              _0: ty_expected
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$7, {
+                cause: {
+                  MEL_EXN_ID: $$Error$7,
+                  _1: loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* Private_type */19,
+                    _0: ty_expected
+                  }
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: $$Error$7,
-          _1: lid.loc,
-          _2: env,
-          _3: {
-            TAG: /* Private_label */20,
-            _0: lid.txt,
-            _1: ty_expected
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$7, {
+              cause: {
+                MEL_EXN_ID: $$Error$7,
+                _1: lid.loc,
+                _2: env,
+                _3: {
+                  TAG: /* Private_label */20,
+                  _0: lid.txt,
+                  _1: ty_expected
+                }
+              }
+            });
   }
   var snap = Caml_obj.caml_equal(vars, /* [] */0) ? undefined : Caml_option.some(snapshot(undefined));
   var arg = type_argument(env, sarg, ty_arg$1, instance(undefined, env, ty_arg$1));
@@ -69418,7 +70976,9 @@ function type_label_exp(create, env, loc, ty_expected, param) {
   }
   catch (exn$1){
     if (is_nonexpansive(arg)) {
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
     try {
       may(backtrack, snap);
@@ -69435,14 +70995,22 @@ function type_label_exp(create, env, loc, ty_expected, param) {
       if (e.MEL_EXN_ID === $$Error$7) {
         var tmp = e._3;
         if (typeof tmp === "number") {
-          throw exn$1;
+          throw new Error(exn$1.MEL_EXN_ID, {
+                    cause: exn$1
+                  });
         }
         if (tmp.TAG === /* Less_general */31) {
-          throw e;
+          throw new Error(e.MEL_EXN_ID, {
+                    cause: e
+                  });
         }
-        throw exn$1;
+        throw new Error(exn$1.MEL_EXN_ID, {
+                  cause: exn$1
+                });
       } else {
-        throw exn$1;
+        throw new Error(exn$1.MEL_EXN_ID, {
+                  cause: exn$1
+                });
       }
     }
   }
@@ -69824,34 +71392,36 @@ function type_application(env, funct, sargs) {
             if (ignore_labels && !is_optional(l)) {
               if (sargs) {
                 var match$5 = sargs.hd;
-                throw {
-                      MEL_EXN_ID: $$Error$7,
-                      _1: match$5[1].pexp_loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Apply_wrong_label */9,
-                        _0: match$5[0],
-                        _1: ty_old
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$7, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$7,
+                            _1: match$5[1].pexp_loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Apply_wrong_label */9,
+                              _0: match$5[0],
+                              _1: ty_old
+                            }
+                          }
+                        });
               }
               if (more_sargs) {
                 var match$6 = more_sargs.hd;
                 var sarg0 = match$6[1];
                 var l$p = match$6[0];
                 if (l !== l$p && l$p !== "") {
-                  throw {
-                        MEL_EXN_ID: $$Error$7,
-                        _1: sarg0.pexp_loc,
-                        _2: env,
-                        _3: {
-                          TAG: /* Apply_wrong_label */9,
-                          _0: l$p,
-                          _1: match
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$7, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$7,
+                              _1: sarg0.pexp_loc,
+                              _2: env,
+                              _3: {
+                                TAG: /* Apply_wrong_label */9,
+                                _0: l$p,
+                                _1: match
+                              }
+                            }
+                          });
                 }
                 match$4 = [
                   /* [] */0,
@@ -69863,15 +71433,16 @@ function type_application(env, funct, sargs) {
                   }(ty,ty0,sarg0))
                 ];
               } else {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        45373,
-                        16
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              45373,
+                              16
+                            ]
+                          }
+                        });
               }
             } else {
               try {
@@ -69912,7 +71483,9 @@ function type_application(env, funct, sargs) {
                       match$9[3]
                     ];
                   } else {
-                    throw exn;
+                    throw new Error(exn.MEL_EXN_ID, {
+                              cause: exn
+                            });
                   }
                 }
                 var sarg0$3 = match$7[1];
@@ -69966,7 +71539,9 @@ function type_application(env, funct, sargs) {
                             }), undefined)
                   ];
                 } else {
-                  throw exn$1;
+                  throw new Error(exn$1.MEL_EXN_ID, {
+                            cause: exn$1
+                          });
                 }
               }
             }
@@ -70005,17 +71580,18 @@ function type_application(env, funct, sargs) {
         if (sargs) {
           if (ignore_labels) {
             var match$10 = sargs.hd;
-            throw {
-                  MEL_EXN_ID: $$Error$7,
-                  _1: match$10[1].pexp_loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* Apply_wrong_label */9,
-                    _0: match$10[0],
-                    _1: ty_old
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$7, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$7,
+                        _1: match$10[1].pexp_loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* Apply_wrong_label */9,
+                          _0: match$10[0],
+                          _1: ty_old
+                        }
+                      }
+                    });
           }
           exit$1 = 2;
         } else {
@@ -70121,39 +71697,42 @@ function type_application(env, funct, sargs) {
               } else {
                 if (match$13.TAG === /* Tarrow */1) {
                   if (classic.contents || !has_label(l1, ty_fun$4)) {
-                    throw {
-                          MEL_EXN_ID: $$Error$7,
-                          _1: sarg1.pexp_loc,
-                          _2: env,
-                          _3: {
-                            TAG: /* Apply_wrong_label */9,
-                            _0: l1,
-                            _1: ty_res
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$7, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$7,
+                                _1: sarg1.pexp_loc,
+                                _2: env,
+                                _3: {
+                                  TAG: /* Apply_wrong_label */9,
+                                  _0: l1,
+                                  _1: ty_res
+                                }
+                              }
+                            });
                   }
-                  throw {
-                        MEL_EXN_ID: $$Error$7,
-                        _1: funct.exp_loc,
-                        _2: env,
-                        _3: /* Incoherent_label_order */1,
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$7, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$7,
+                              _1: funct.exp_loc,
+                              _2: env,
+                              _3: /* Incoherent_label_order */1
+                            }
+                          });
                 }
                 exit$3 = 2;
               }
               if (exit$3 === 2) {
-                throw {
-                      MEL_EXN_ID: $$Error$7,
-                      _1: funct.exp_loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Apply_non_function */8,
-                        _0: expand_head(env, funct.exp_type)
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$7, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$7,
+                            _1: funct.exp_loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Apply_non_function */8,
+                              _0: expand_head(env, funct.exp_type)
+                            }
+                          }
+                        });
               }
               
             }
@@ -70482,18 +72061,21 @@ function type_cases(in_function, env, ty_arg, ty_res, partial_flag, loc, caselis
             if (exn.MEL_EXN_ID === Empty || exn.MEL_EXN_ID === Stdlib.Not_found || exn.MEL_EXN_ID === NoGuard) {
               exit = 1;
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
             if (exit === 1) {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      40982,
-                      48
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            40982,
+                            48
+                          ]
+                        }
+                      });
             }
             
           }
@@ -70721,7 +72303,9 @@ function type_let(checkOpt, check_strictOpt, env, rec_flag, spat_sexp_list, scop
                     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                       return Stdlib__Hashtbl.add(value_declarations, key, callback);
                     }
-                    throw exn;
+                    throw new Error(exn.MEL_EXN_ID, {
+                              cause: exn
+                            });
                   }
                 }), pat_bound_idents(pat));
           return [
@@ -72035,15 +73619,16 @@ register_error_of_exn(function (param) {
                                                                         return type_path_expansion(tp0, param, param$1);
                                                                       }), tp0$p);
                                                         }
-                                                        throw {
-                                                              MEL_EXN_ID: "Assert_failure",
-                                                              _1: [
-                                                                "jscomp/test/ocaml_typedtree_test.ml",
-                                                                37069,
-                                                                12
-                                                              ],
-                                                              Error: new Error()
-                                                            };
+                                                        throw new Error("Assert_failure", {
+                                                                  cause: {
+                                                                    MEL_EXN_ID: "Assert_failure",
+                                                                    _1: [
+                                                                      "jscomp/test/ocaml_typedtree_test.ml",
+                                                                      37069,
+                                                                      12
+                                                                    ]
+                                                                  }
+                                                                });
                                                       }));
                                       case /* Invalid_format */15 :
                                           return Curry._1(Stdlib__Format.fprintf(param)(/* Format */{
@@ -72898,28 +74483,30 @@ function set_fixed_row(env, loc, p, decl) {
   if (t !== undefined) {
     tm = expand_head(env, t);
   } else {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            46327,
-            14
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  46327,
+                  14
+                ]
+              }
+            });
   }
   var row = tm.desc;
   var rv;
   if (typeof row === "number") {
-    throw {
-          MEL_EXN_ID: $$Error$8,
-          _1: loc,
-          _2: {
-            TAG: /* Bad_fixed_type */18,
-            _0: "is not an object or variant"
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$8, {
+              cause: {
+                MEL_EXN_ID: $$Error$8,
+                _1: loc,
+                _2: {
+                  TAG: /* Bad_fixed_type */18,
+                  _0: "is not an object or variant"
+                }
+              }
+            });
   }
   switch (row.TAG | 0) {
     case /* Tobject */4 :
@@ -72941,26 +74528,28 @@ function set_fixed_row(env, loc, p, decl) {
         rv = static_row(row$1) ? newty2(100000000, /* Tnil */0) : row$1.row_more;
         break;
     default:
-      throw {
-            MEL_EXN_ID: $$Error$8,
-            _1: loc,
-            _2: {
-              TAG: /* Bad_fixed_type */18,
-              _0: "is not an object or variant"
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$8, {
+                cause: {
+                  MEL_EXN_ID: $$Error$8,
+                  _1: loc,
+                  _2: {
+                    TAG: /* Bad_fixed_type */18,
+                    _0: "is not an object or variant"
+                  }
+                }
+              });
   }
   if (!is_Tvar(rv)) {
-    throw {
-          MEL_EXN_ID: $$Error$8,
-          _1: loc,
-          _2: {
-            TAG: /* Bad_fixed_type */18,
-            _0: "has no row variable"
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$8, {
+              cause: {
+                MEL_EXN_ID: $$Error$8,
+                _1: loc,
+                _2: {
+                  TAG: /* Bad_fixed_type */18,
+                  _0: "has no row variable"
+                }
+              }
+            });
   }
   rv.desc = {
     TAG: /* Tconstr */3,
@@ -73011,17 +74600,19 @@ function bal$10(l, v, r) {
       if (lr) {
         return create$11(create$11(ll, lv, lr.l), lr.v, create$11(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -73041,17 +74632,19 @@ function bal$10(l, v, r) {
     if (rl) {
       return create$11(create$11(l, v, rl.l), rl.v, create$11(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$12(x, t) {
@@ -73113,14 +74706,17 @@ function make_params(env, params) {
     catch (raw_exn){
       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
       if (exn.MEL_EXN_ID === Already_bound) {
-        throw {
-              MEL_EXN_ID: $$Error$8,
-              _1: sty.ptyp_loc,
-              _2: /* Repeated_parameter */0,
-              Error: new Error()
-            };
+        throw new Error($$Error$8, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$8,
+                    _1: sty.ptyp_loc,
+                    _2: /* Repeated_parameter */0
+                  }
+                });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   return Stdlib__List.map(make_param, params);
@@ -73144,16 +74740,17 @@ function make_constructor(env, type_path, type_params, sargs, sret_type) {
       exit = 1;
     }
     if (exit === 1) {
-      throw {
-            MEL_EXN_ID: $$Error$8,
-            _1: sret_type.ptyp_loc,
-            _2: {
-              TAG: /* Constraint_failed */5,
-              _0: ret_type,
-              _1: newconstr(type_path, type_params)
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$8, {
+                cause: {
+                  MEL_EXN_ID: $$Error$8,
+                  _1: sret_type.ptyp_loc,
+                  _2: {
+                    TAG: /* Constraint_failed */5,
+                    _0: ret_type,
+                    _1: newconstr(type_path, type_params)
+                  }
+                }
+              });
     }
     widen(z);
     return [
@@ -73231,40 +74828,45 @@ function check_constraints_rec(env, loc, visited, _ty) {
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      46574,
-                      28
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            46574,
+                            28
+                          ]
+                        }
+                      });
             }
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-              throw {
-                    MEL_EXN_ID: $$Error$8,
-                    _1: loc,
-                    _2: {
-                      TAG: /* Unavailable_type_constructor */17,
-                      _0: path
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$8, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$8,
+                          _1: loc,
+                          _2: {
+                            TAG: /* Unavailable_type_constructor */17,
+                            _0: path
+                          }
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           if (!matches(env, ty$1, ty$p)) {
-            throw {
-                  MEL_EXN_ID: $$Error$8,
-                  _1: loc,
-                  _2: {
-                    TAG: /* Constraint_failed */5,
-                    _0: ty$1,
-                    _1: ty$p
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$8, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$8,
+                        _1: loc,
+                        _2: {
+                          TAG: /* Constraint_failed */5,
+                          _0: ty$1,
+                          _1: ty$p
+                        }
+                      }
+                    });
           }
           return Stdlib__List.iter((function (param) {
                         return check_constraints_rec(env, loc, visited, param);
@@ -73320,17 +74922,19 @@ function bal$11(l, x, d, r) {
       if (lr) {
         return create$12(create$12(ll, lv, ld, lr.l), lr.v, lr.d, create$12(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -73352,17 +74956,19 @@ function bal$11(l, x, d, r) {
     if (rl) {
       return create$12(create$12(l, x, d, rl.l), rl.v, rl.d, create$12(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add$13(x, data, m) {
@@ -73420,10 +75026,11 @@ function find$6(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -73438,16 +75045,17 @@ function check_coherence(env, loc, id, decl) {
   }
   var match$1 = repr(ty).desc;
   if (typeof match$1 === "number") {
-    throw {
-          MEL_EXN_ID: $$Error$8,
-          _1: loc,
-          _2: {
-            TAG: /* Definition_mismatch */4,
-            _0: ty,
-            _1: /* [] */0
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$8, {
+              cause: {
+                MEL_EXN_ID: $$Error$8,
+                _1: loc,
+                _2: {
+                  TAG: /* Definition_mismatch */4,
+                  _0: ty,
+                  _1: /* [] */0
+                }
+              }
+            });
   }
   if (match$1.TAG === /* Tconstr */3) {
     var args = match$1._1;
@@ -73466,43 +75074,48 @@ function check_coherence(env, loc, id, decl) {
       if (!Caml_obj.caml_notequal(err, /* [] */0)) {
         return ;
       }
-      throw {
-            MEL_EXN_ID: $$Error$8,
-            _1: loc,
-            _2: {
-              TAG: /* Definition_mismatch */4,
-              _0: ty,
-              _1: err
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$8, {
+                cause: {
+                  MEL_EXN_ID: $$Error$8,
+                  _1: loc,
+                  _2: {
+                    TAG: /* Definition_mismatch */4,
+                    _0: ty,
+                    _1: err
+                  }
+                }
+              });
     }
     catch (raw_exn){
       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-        throw {
-              MEL_EXN_ID: $$Error$8,
-              _1: loc,
-              _2: {
-                TAG: /* Unavailable_type_constructor */17,
-                _0: path
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$8, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$8,
+                    _1: loc,
+                    _2: {
+                      TAG: /* Unavailable_type_constructor */17,
+                      _0: path
+                    }
+                  }
+                });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   } else {
-    throw {
-          MEL_EXN_ID: $$Error$8,
-          _1: loc,
-          _2: {
-            TAG: /* Definition_mismatch */4,
-            _0: ty,
-            _1: /* [] */0
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$8, {
+              cause: {
+                MEL_EXN_ID: $$Error$8,
+                _1: loc,
+                _2: {
+                  TAG: /* Definition_mismatch */4,
+                  _0: ty,
+                  _1: /* [] */0
+                }
+              }
+            });
   }
 }
 
@@ -73517,26 +75130,28 @@ function check_well_founded(env, loc, path, to_check, ty) {
       var tmp;
       tmp = typeof match === "number" || match.TAG !== /* Tconstr */3 ? false : same(match._0, path);
       if (tmp) {
-        throw {
-              MEL_EXN_ID: $$Error$8,
-              _1: loc,
-              _2: {
-                TAG: /* Recursive_abbrev */2,
-                _0: name(undefined, path)
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$8, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$8,
+                    _1: loc,
+                    _2: {
+                      TAG: /* Recursive_abbrev */2,
+                      _0: name(undefined, path)
+                    }
+                  }
+                });
       }
-      throw {
-            MEL_EXN_ID: $$Error$8,
-            _1: loc,
-            _2: {
-              TAG: /* Cycle_in_def */3,
-              _0: name(undefined, path),
-              _1: ty0
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$8, {
+                cause: {
+                  MEL_EXN_ID: $$Error$8,
+                  _1: loc,
+                  _2: {
+                    TAG: /* Cycle_in_def */3,
+                    _0: name(undefined, path),
+                    _1: ty0
+                  }
+                }
+              });
     }
     var match$1;
     try {
@@ -73557,7 +75172,9 @@ function check_well_founded(env, loc, path, to_check, ty) {
           exp_nodes
         ];
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
     var exp_nodes$1 = match$1[1];
@@ -73569,10 +75186,11 @@ function check_well_founded(env, loc, path, to_check, ty) {
       visited.contents = Curry._3(add$4, ty$1, exp_nodes$1, visited.contents);
       var match$2 = ty$1.desc;
       if (typeof match$2 === "number") {
-        throw {
-              MEL_EXN_ID: Cannot_expand,
-              Error: new Error()
-            };
+        throw new Error(Cannot_expand, {
+                  cause: {
+                    MEL_EXN_ID: Cannot_expand
+                  }
+                });
       }
       if (match$2.TAG === /* Tconstr */3) {
         if (!Curry._1(is_empty$2, exp_nodes$1) || Curry._1(to_check, match$2._0)) {
@@ -73580,15 +75198,17 @@ function check_well_founded(env, loc, path, to_check, ty) {
           var ty0$1 = Curry._1(is_empty$2, exp_nodes$1) ? ty$1 : ty0;
           return check(ty0$1, Curry._2(add$3, ty$1, exp_nodes$1), ty$p);
         }
-        throw {
-              MEL_EXN_ID: Cannot_expand,
-              Error: new Error()
-            };
+        throw new Error(Cannot_expand, {
+                  cause: {
+                    MEL_EXN_ID: Cannot_expand
+                  }
+                });
       }
-      throw {
-            MEL_EXN_ID: Cannot_expand,
-            Error: new Error()
-          };
+      throw new Error(Cannot_expand, {
+                cause: {
+                  MEL_EXN_ID: Cannot_expand
+                }
+              });
     }
     catch (raw_exn$1){
       var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
@@ -73619,7 +75239,9 @@ function check_well_founded(env, loc, path, to_check, ty) {
       if (exn$1.MEL_EXN_ID === Unify) {
         return backtrack(snap);
       }
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
   };
   wrap_trace_gadt_instances(env, (function (param) {
@@ -73683,17 +75305,18 @@ function check_recursion(env, loc, path, decl, to_check) {
             var path$p = match._0;
             if (same(path, path$p)) {
               if (!equal$5(env, false, args, args$p)) {
-                throw {
-                      MEL_EXN_ID: $$Error$8,
-                      _1: loc,
-                      _2: {
-                        TAG: /* Parameters_differ */8,
-                        _0: cpath,
-                        _1: ty$1,
-                        _2: newconstr(path, args)
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$8, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$8,
+                            _1: loc,
+                            _2: {
+                              TAG: /* Parameters_differ */8,
+                              _0: cpath,
+                              _1: ty$1,
+                              _2: newconstr(path, args)
+                            }
+                          }
+                        });
               }
               
             } else if (Curry._1(to_check, path$p) && !Stdlib__List.mem(path$p, prev_exp)) {
@@ -73709,18 +75332,21 @@ function check_recursion(env, loc, path, decl, to_check) {
                 catch (raw_exn){
                   var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                   if (exn.MEL_EXN_ID === Unify) {
-                    throw {
-                          MEL_EXN_ID: $$Error$8,
-                          _1: loc,
-                          _2: {
-                            TAG: /* Constraint_failed */5,
-                            _0: ty$1,
-                            _1: newconstr(path$p, params0)
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$8, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$8,
+                                _1: loc,
+                                _2: {
+                                  TAG: /* Constraint_failed */5,
+                                  _0: ty$1,
+                                  _1: newconstr(path$p, params0)
+                                }
+                              }
+                            });
                   }
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
                 check_regular(path$p, args, {
                       hd: path$p,
@@ -73730,7 +75356,9 @@ function check_recursion(env, loc, path, decl, to_check) {
               catch (raw_exn$1){
                 var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
                 if (exn$1.MEL_EXN_ID !== Stdlib.Not_found) {
-                  throw exn$1;
+                  throw new Error(exn$1.MEL_EXN_ID, {
+                            cause: exn$1
+                          });
                 }
                 
               }
@@ -73764,7 +75392,9 @@ function get_variance(ty, visited) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return Types_Variance.$$null;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -73828,7 +75458,9 @@ function compute_variance(env, visited, vari, ty) {
                               return compute_variance_rec(Types_Variance.may_inv, param);
                             }), tl$1);
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
         case /* Tfield */5 :
             compute_variance_rec(vari$1, tl._2);
@@ -73941,25 +75573,26 @@ function compute_variance_type(env, check, param, decl, tyl) {
             if (!(is_Tvar(ty) && (co && !c || cn && !n || !ij && i))) {
               return ;
             }
-            throw {
-                  MEL_EXN_ID: $$Error$8,
-                  _1: loc,
-                  _2: {
-                    TAG: /* Bad_variance */16,
-                    _0: pos.contents,
-                    _1: [
-                      co,
-                      cn,
-                      ij
-                    ],
-                    _2: [
-                      c,
-                      n,
-                      i
-                    ]
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$8, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$8,
+                        _1: loc,
+                        _2: {
+                          TAG: /* Bad_variance */16,
+                          _0: pos.contents,
+                          _1: [
+                            co,
+                            cn,
+                            ij
+                          ],
+                          _2: [
+                            c,
+                            n,
+                            i
+                          ]
+                        }
+                      }
+                    });
           }), params, required);
     var args = newty2(100000000, {
           TAG: /* Ttuple */2,
@@ -74023,25 +75656,26 @@ function compute_variance_type(env, check, param, decl, tyl) {
         var code = match$1[3] ? (
             c2 || n2 ? -1 : -3
           ) : -2;
-        throw {
-              MEL_EXN_ID: $$Error$8,
-              _1: loc,
-              _2: {
-                TAG: /* Bad_variance */16,
-                _0: code,
-                _1: [
-                  c1,
-                  n1,
-                  false
-                ],
-                _2: [
-                  c2,
-                  n2,
-                  false
-                ]
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$8, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$8,
+                    _1: loc,
+                    _2: {
+                      TAG: /* Bad_variance */16,
+                      _0: code,
+                      _1: [
+                        c1,
+                        n1,
+                        false
+                      ],
+                      _2: [
+                        c2,
+                        n2,
+                        false
+                      ]
+                    }
+                  }
+                });
       };
       Stdlib__List.iter((function (param) {
               check$1(param[1]);
@@ -74119,15 +75753,16 @@ function compute_variance_gadt(env, check, rloc, decl, param) {
   var match = repr(ret_type_opt);
   var match$1 = match.desc;
   if (typeof match$1 === "number") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/ocaml_typedtree_test.ml",
-            47023,
-            13
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/ocaml_typedtree_test.ml",
+                  47023,
+                  13
+                ]
+              }
+            });
   }
   if (match$1.TAG === /* Tconstr */3) {
     var tyl = Stdlib__List.map(repr, match$1._1);
@@ -74140,12 +75775,13 @@ function compute_variance_gadt(env, check, rloc, decl, param) {
               var fv2$1 = fv2.tl;
               var fv1 = param[0];
               if ((param$1[0] || param$1[1]) && constrained(env, Stdlib.$at(fv1, fv2$1), ty)) {
-                throw {
-                      MEL_EXN_ID: $$Error$8,
-                      _1: loc,
-                      _2: /* Varying_anonymous */4,
-                      Error: new Error()
-                    };
+                throw new Error($$Error$8, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$8,
+                            _1: loc,
+                            _2: /* Varying_anonymous */4
+                          }
+                        });
               }
               return [
                       {
@@ -74155,15 +75791,16 @@ function compute_variance_gadt(env, check, rloc, decl, param) {
                       fv2$1
                     ];
             }
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    47012,
-                    37
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          47012,
+                          37
+                        ]
+                      }
+                    });
           }), [
           /* [] */0,
           fvl
@@ -74180,15 +75817,16 @@ function compute_variance_gadt(env, check, rloc, decl, param) {
                 type_attributes: decl.type_attributes
               }, add_false(tl));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          47023,
-          13
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                47023,
+                13
+              ]
+            }
+          });
 }
 
 function compute_variance_extension(env, check, decl, ext, rloc) {
@@ -74272,15 +75910,16 @@ function compute_variance_decl(env, check, decl, rloc) {
                   }
                 }), varl);
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/ocaml_typedtree_test.ml",
-          47062,
-          15
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/ocaml_typedtree_test.ml",
+                47062,
+                15
+              ]
+            }
+          });
 }
 
 function is_sharp(id) {
@@ -74471,7 +76110,9 @@ function check_duplicates(sdecl_list) {
                             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                               return Stdlib__Hashtbl.add(constrs, pcd.pcd_name.txt, sdecl.ptype_name.txt);
                             }
-                            throw exn;
+                            throw new Error(exn.MEL_EXN_ID, {
+                                      cause: exn
+                                    });
                           }
                         }), cl._0);
           } else {
@@ -74492,7 +76133,9 @@ function check_duplicates(sdecl_list) {
                             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                               return Stdlib__Hashtbl.add(labels, cname.txt, sdecl.ptype_name.txt);
                             }
-                            throw exn;
+                            throw new Error(exn.MEL_EXN_ID, {
+                                      cause: exn
+                                    });
                           }
                         }), cl._0);
           }
@@ -74664,27 +76307,29 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
       Stdlib__List.iter((function (param) {
               var name = param.pcd_name.txt;
               if (Curry._2(mem$6, name, all_constrs.contents)) {
-                throw {
-                      MEL_EXN_ID: $$Error$8,
-                      _1: name_sdecl.ptype_loc,
-                      _2: {
-                        TAG: /* Duplicate_constructor */0,
-                        _0: name
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$8, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$8,
+                            _1: name_sdecl.ptype_loc,
+                            _2: {
+                              TAG: /* Duplicate_constructor */0,
+                              _0: name
+                            }
+                          }
+                        });
               }
               all_constrs.contents = Curry._2(add$12, name, all_constrs.contents);
             }), scstrs$1);
       if (Stdlib__List.length(Stdlib__List.filter((function (cd) {
                     return Caml_obj.caml_notequal(cd.pcd_args, /* [] */0);
                   }), scstrs$1)) > 246) {
-        throw {
-              MEL_EXN_ID: $$Error$8,
-              _1: name_sdecl.ptype_loc,
-              _2: /* Too_many_constructors */1,
-              Error: new Error()
-            };
+        throw new Error($$Error$8, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$8,
+                    _1: name_sdecl.ptype_loc,
+                    _2: /* Too_many_constructors */1
+                  }
+                });
       }
       var make_cstr = function (scstr) {
         var name = create(scstr.pcd_name.txt);
@@ -74743,15 +76388,16 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
       Stdlib__List.iter((function (param) {
               var name = param.pld_name.txt;
               if (Curry._2(mem$6, name, all_labels.contents)) {
-                throw {
-                      MEL_EXN_ID: $$Error$8,
-                      _1: name_sdecl.ptype_loc,
-                      _2: {
-                        TAG: /* Duplicate_label */1,
-                        _0: name
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$8, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$8,
+                            _1: name_sdecl.ptype_loc,
+                            _2: {
+                              TAG: /* Duplicate_label */1,
+                              _0: name
+                            }
+                          }
+                        });
               }
               all_labels.contents = Curry._2(add$12, name, all_labels.contents);
             }), lbls);
@@ -74847,18 +76493,21 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Unify) {
-                throw {
-                      MEL_EXN_ID: $$Error$8,
-                      _1: param[2],
-                      _2: {
-                        TAG: /* Inconsistent_constraint */6,
-                        _0: temp_env,
-                        _1: exn._1
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$8, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$8,
+                            _1: param[2],
+                            _2: {
+                              TAG: /* Inconsistent_constraint */6,
+                              _0: temp_env,
+                              _1: exn._1
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }), cstrs);
     end_def(undefined);
@@ -74873,30 +76522,34 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
       catch (raw_exn){
         var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
         if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  46515,
-                  26
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        46515,
+                        26
+                      ]
+                    }
+                  });
         }
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
       set_fixed_row(temp_env, name_sdecl.ptype_loc, match$3[0], decl);
     }
     if (man !== undefined && cyclic_abbrev(temp_env, id, man)) {
-      throw {
-            MEL_EXN_ID: $$Error$8,
-            _1: name_sdecl.ptype_loc,
-            _2: {
-              TAG: /* Recursive_abbrev */2,
-              _0: name_sdecl.ptype_name.txt
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$8, {
+                cause: {
+                  MEL_EXN_ID: $$Error$8,
+                  _1: name_sdecl.ptype_loc,
+                  _2: {
+                    TAG: /* Recursive_abbrev */2,
+                    _0: name_sdecl.ptype_name.txt
+                  }
+                }
+              });
     }
     return {
             typ_id: id,
@@ -74944,18 +76597,21 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Unify) {
-                throw {
-                      MEL_EXN_ID: $$Error$8,
-                      _1: loc,
-                      _2: {
-                        TAG: /* Type_clash */7,
-                        _0: newenv,
-                        _1: exn._1
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$8, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$8,
+                            _1: loc,
+                            _2: {
+                              TAG: /* Type_clash */7,
+                              _0: newenv,
+                              _1: exn._1
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }), id_list, sdecl_list$1);
   }
@@ -75018,16 +76674,17 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
           if (ty === undefined) {
             return ;
           }
-          throw {
-                MEL_EXN_ID: $$Error$8,
-                _1: sdecl.ptype_loc,
-                _2: {
-                  TAG: /* Unbound_type_var */9,
-                  _0: ty,
-                  _1: decl
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$8, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$8,
+                      _1: sdecl.ptype_loc,
+                      _2: {
+                        TAG: /* Unbound_type_var */9,
+                        _0: ty,
+                        _1: decl
+                      }
+                    }
+                  });
         }), sdecl_list$1, tdecls);
   Stdlib__List.iter2((function (param, param$1) {
           var decl = param$1[1];
@@ -75040,28 +76697,30 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
           } else if (l.TAG === /* Type_record */0) {
             var find_pl = function (param) {
               if (typeof param === "number") {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        46623,
-                        59
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              46623,
+                              59
+                            ]
+                          }
+                        });
               }
               if (param.TAG === /* Ptype_record */1) {
                 return param._0;
               }
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      46623,
-                      59
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            46623,
+                            59
+                          ]
+                        }
+                      });
             };
             var pl = find_pl(param.ptype_kind);
             var get_loc = function (name, _param) {
@@ -75075,15 +76734,16 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
                   _param = param.tl;
                   continue ;
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        46627,
-                        16
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              46627,
+                              16
+                            ]
+                          }
+                        });
               };
             };
             Stdlib__List.iter((function (param) {
@@ -75092,28 +76752,30 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
           } else {
             var find_pl$1 = function (param) {
               if (typeof param === "number") {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        46596,
-                        58
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              46596,
+                              58
+                            ]
+                          }
+                        });
               }
               if (param.TAG === /* Ptype_variant */0) {
                 return param._0;
               }
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      46596,
-                      58
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            46596,
+                            58
+                          ]
+                        }
+                      });
             };
             var pl$1 = find_pl$1(param.ptype_kind);
             var foldf = function (acc, x) {
@@ -75129,17 +76791,20 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
                     catch (raw_exn){
                       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-                        throw {
-                              MEL_EXN_ID: "Assert_failure",
-                              _1: [
-                                "jscomp/test/ocaml_typedtree_test.ml",
-                                46609,
-                                30
-                              ],
-                              Error: new Error()
-                            };
+                        throw new Error("Assert_failure", {
+                                  cause: {
+                                    MEL_EXN_ID: "Assert_failure",
+                                    _1: [
+                                      "jscomp/test/ocaml_typedtree_test.ml",
+                                      46609,
+                                      30
+                                    ]
+                                  }
+                                });
                       }
-                      throw exn;
+                      throw new Error(exn.MEL_EXN_ID, {
+                                cause: exn
+                              });
                     }
                     var sret_type = match.pcd_res;
                     Stdlib__List.iter2((function (sty, ty) {
@@ -75160,15 +76825,16 @@ function transl_type_decl(env, rec_flag, sdecl_list) {
           if (sty !== undefined) {
             sty$1 = sty;
           } else {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/ocaml_typedtree_test.ml",
-                    46642,
-                    63
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/ocaml_typedtree_test.ml",
+                          46642,
+                          63
+                        ]
+                      }
+                    });
           }
           return check_constraints_rec(newenv, sty$1.ptyp_loc, visited, ty);
         }), sdecl_list$1, decls);
@@ -75256,19 +76922,22 @@ function transl_extension_constructor(env, check_open, type_path, type_params, t
     catch (raw_exn){
       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
       if (exn.MEL_EXN_ID === Unify) {
-        throw {
-              MEL_EXN_ID: $$Error$8,
-              _1: lid$1.loc,
-              _2: {
-                TAG: /* Rebind_wrong_type */13,
-                _0: lid$1.txt,
-                _1: env,
-                _2: exn._1
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$8, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$8,
+                    _1: lid$1.loc,
+                    _2: {
+                      TAG: /* Rebind_wrong_type */13,
+                      _0: lid$1.txt,
+                      _1: env,
+                      _2: exn._1
+                    }
+                  }
+                });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
     if (!cdescr.cstr_generalized) {
       var vars = free_variables$1(undefined, newty2(100000000, {
@@ -75297,15 +76966,16 @@ function transl_extension_constructor(env, check_open, type_path, type_params, t
     var match$4 = cdescr.cstr_res.desc;
     var match$5;
     if (typeof match$4 === "number") {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              47376,
-              17
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    47376,
+                    17
+                  ]
+                }
+              });
     }
     if (match$4.TAG === /* Tconstr */3) {
       var p = match$4._0;
@@ -75315,15 +76985,16 @@ function transl_extension_constructor(env, check_open, type_path, type_params, t
         decl.type_params
       ];
     } else {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              47376,
-              17
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    47376,
+                    17
+                  ]
+                }
+              });
     }
     var cstr_type_params = match$5[1];
     var cstr_type_path = match$5[0];
@@ -75352,44 +77023,47 @@ function transl_extension_constructor(env, check_open, type_path, type_params, t
       tl: type_params
     };
     if (!equal$5(env, true, cstr_types, ext_types)) {
-      throw {
-            MEL_EXN_ID: $$Error$8,
-            _1: lid$1.loc,
-            _2: {
-              TAG: /* Rebind_mismatch */14,
-              _0: lid$1.txt,
-              _1: cstr_type_path,
-              _2: type_path
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$8, {
+                cause: {
+                  MEL_EXN_ID: $$Error$8,
+                  _1: lid$1.loc,
+                  _2: {
+                    TAG: /* Rebind_mismatch */14,
+                    _0: lid$1.txt,
+                    _1: cstr_type_path,
+                    _2: type_path
+                  }
+                }
+              });
     }
     var match$6 = cdescr.cstr_private;
     if (!match$6 && priv) {
-      throw {
-            MEL_EXN_ID: $$Error$8,
-            _1: lid$1.loc,
-            _2: {
-              TAG: /* Rebind_private */15,
-              _0: lid$1.txt
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$8, {
+                cause: {
+                  MEL_EXN_ID: $$Error$8,
+                  _1: lid$1.loc,
+                  _2: {
+                    TAG: /* Rebind_private */15,
+                    _0: lid$1.txt
+                  }
+                }
+              });
     }
     var match$7 = cdescr.cstr_tag;
     var path;
     switch (match$7.TAG | 0) {
       case /* Cstr_constant */0 :
       case /* Cstr_block */1 :
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  47401,
-                  17
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        47401,
+                        17
+                      ]
+                    }
+                  });
       case /* Cstr_extension */2 :
           path = match$7._0;
           break;
@@ -75445,35 +77119,39 @@ function transl_type_extension(check_open, env, loc, styext) {
                   return false;
                 }
               }), styext.ptyext_constructors);
-        throw {
-              MEL_EXN_ID: $$Error$8,
-              _1: match$2.pext_loc,
-              _2: {
-                TAG: /* Not_open_type */10,
-                _0: type_path
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$8, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$8,
+                    _1: match$2.pext_loc,
+                    _2: {
+                      TAG: /* Not_open_type */10,
+                      _0: type_path
+                    }
+                  }
+                });
       }
       catch (raw_exn){
         var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
         if (exn.MEL_EXN_ID !== Stdlib.Not_found) {
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         }
         
       }
     }
     
   } else {
-    throw {
-          MEL_EXN_ID: $$Error$8,
-          _1: loc,
-          _2: {
-            TAG: /* Not_extensible_type */11,
-            _0: type_path
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$8, {
+              cause: {
+                MEL_EXN_ID: $$Error$8,
+                _1: loc,
+                _2: {
+                  TAG: /* Not_extensible_type */11,
+                  _0: type_path
+                }
+              }
+            });
   }
   var type_variance = Stdlib__List.map((function (v) {
           var match = Curry._1(Types_Variance.get_upper, v);
@@ -75505,16 +77183,17 @@ function transl_type_extension(check_open, env, loc, styext) {
           })
     );
   if (Caml_obj.caml_notequal(err, /* [] */0)) {
-    throw {
-          MEL_EXN_ID: $$Error$8,
-          _1: loc,
-          _2: {
-            TAG: /* Extension_mismatch */12,
-            _0: type_path,
-            _1: err
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$8, {
+              cause: {
+                MEL_EXN_ID: $$Error$8,
+                _1: loc,
+                _2: {
+                  TAG: /* Extension_mismatch */12,
+                  _0: type_path,
+                  _1: err
+                }
+              }
+            });
   }
   var ttype_params = make_params(env, styext.ptyext_params);
   var type_params = Stdlib__List.map((function (param) {
@@ -75539,16 +77218,17 @@ function transl_type_extension(check_open, env, loc, styext) {
           if (ty === undefined) {
             return ;
           }
-          throw {
-                MEL_EXN_ID: $$Error$8,
-                _1: ext.ext_loc,
-                _2: {
-                  TAG: /* Unbound_type_var_ext */19,
-                  _0: ty,
-                  _1: ext.ext_type
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$8, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$8,
+                      _1: ext.ext_loc,
+                      _2: {
+                        TAG: /* Unbound_type_var_ext */19,
+                        _0: ty,
+                        _1: ext.ext_type
+                      }
+                    }
+                  });
         }), constructors);
   Stdlib__List.iter((function (ext) {
           compute_variance_extension(env, true, type_decl, ext.ext_type, [
@@ -75585,16 +77265,17 @@ function transl_exception(env, sext) {
   may(generalize, ext.ext_type.ext_ret_type);
   var ty = closed_extension_constructor(ext.ext_type);
   if (ty !== undefined) {
-    throw {
-          MEL_EXN_ID: $$Error$8,
-          _1: ext.ext_loc,
-          _2: {
-            TAG: /* Unbound_type_var_ext */19,
-            _0: ty,
-            _1: ext.ext_type
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$8, {
+              cause: {
+                MEL_EXN_ID: $$Error$8,
+                _1: ext.ext_loc,
+                _2: {
+                  TAG: /* Unbound_type_var_ext */19,
+                  _0: ty,
+                  _1: ext.ext_type
+                }
+              }
+            });
   }
   var newenv = add_extension(true, ext.ext_id, ext.ext_type, env);
   return [
@@ -75659,20 +77340,22 @@ function transl_value_decl(env, loc, valdecl) {
     var prim = parse_declaration(arity$1, decl);
     var prim_native_name = prim.prim_native_name;
     if (arity$1 === 0 && !(prim_native_name.length > 3 && prim_native_name[0] === "B" && prim_native_name[1] === "S" && prim_native_name[2] === ":") && (prim.prim_name.length === 0 || Caml_string.get(prim.prim_name, 0) !== /* '%' */37 && Caml_string.get(prim.prim_name, 0) !== /* '#' */35)) {
-      throw {
-            MEL_EXN_ID: $$Error$8,
-            _1: valdecl.pval_type.ptyp_loc,
-            _2: /* Null_arity_external */2,
-            Error: new Error()
-          };
+      throw new Error($$Error$8, {
+                cause: {
+                  MEL_EXN_ID: $$Error$8,
+                  _1: valdecl.pval_type.ptyp_loc,
+                  _2: /* Null_arity_external */2
+                }
+              });
     }
     if (native_code.contents && prim.prim_arity > 5 && prim_native_name === "") {
-      throw {
-            MEL_EXN_ID: $$Error$8,
-            _1: valdecl.pval_type.ptyp_loc,
-            _2: /* Missing_native_external */3,
-            Error: new Error()
-          };
+      throw new Error($$Error$8, {
+                cause: {
+                  MEL_EXN_ID: $$Error$8,
+                  _1: valdecl.pval_type.ptyp_loc,
+                  _2: /* Missing_native_external */3
+                }
+              });
     }
     v = {
       val_type: ty,
@@ -75749,18 +77432,21 @@ function transl_with_constraint(env, id, row_path, orig_decl, sdecl) {
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$8,
-                    _1: loc,
-                    _2: {
-                      TAG: /* Inconsistent_constraint */6,
-                      _0: env,
-                      _1: exn._1
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$8, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$8,
+                          _1: loc,
+                          _2: {
+                            TAG: /* Inconsistent_constraint */6,
+                            _0: env,
+                            _1: exn._1
+                          }
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }), sdecl.ptype_cstrs);
   var no_row = !is_fixed_type(sdecl);
@@ -75808,16 +77494,17 @@ function transl_with_constraint(env, id, row_path, orig_decl, sdecl) {
   }
   var ty = closed_type_decl(decl);
   if (ty !== undefined) {
-    throw {
-          MEL_EXN_ID: $$Error$8,
-          _1: sdecl.ptype_loc,
-          _2: {
-            TAG: /* Unbound_type_var */9,
-            _0: ty,
-            _1: decl
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$8, {
+              cause: {
+                MEL_EXN_ID: $$Error$8,
+                _1: sdecl.ptype_loc,
+                _2: {
+                  TAG: /* Unbound_type_var */9,
+                  _0: ty,
+                  _1: decl
+                }
+              }
+            });
   }
   var decl$1 = name_recursion(sdecl, id, decl);
   var decl_type_params = decl$1.type_params;
@@ -75999,7 +77686,9 @@ function explain_unbound(ppf, tv, tl, typ, kwd, lab) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -77618,17 +79307,18 @@ function enter_val(cl_num, vars, inh, lab, mut, virt, ty, val_env, met_env, par_
     var match$1 = Curry._2(Meths.find, lab, vars.contents);
     var virt$p = match$1[2];
     if (match$1[1] !== mut) {
-      throw {
-            MEL_EXN_ID: $$Error$9,
-            _1: loc,
-            _2: val_env,
-            _3: {
-              TAG: /* Mutability_mismatch */22,
-              _0: lab,
-              _1: mut
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$9, {
+                cause: {
+                  MEL_EXN_ID: $$Error$9,
+                  _1: loc,
+                  _2: val_env,
+                  _3: {
+                    TAG: /* Mutability_mismatch */22,
+                    _0: lab,
+                    _1: mut
+                  }
+                }
+              });
     }
     unify$2(val_env, instance(undefined, val_env, ty), instance(undefined, val_env, match$1[3]));
     match = [
@@ -77639,18 +79329,19 @@ function enter_val(cl_num, vars, inh, lab, mut, virt, ty, val_env, met_env, par_
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: $$Error$9,
-            _1: loc,
-            _2: val_env,
-            _3: {
-              TAG: /* Field_type_mismatch */1,
-              _0: "instance variable",
-              _1: lab,
-              _2: exn._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$9, {
+                cause: {
+                  MEL_EXN_ID: $$Error$9,
+                  _1: loc,
+                  _2: val_env,
+                  _3: {
+                    TAG: /* Field_type_mismatch */1,
+                    _0: "instance variable",
+                    _1: lab,
+                    _2: exn._1
+                  }
+                }
+              });
     }
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       match = [
@@ -77658,7 +79349,9 @@ function enter_val(cl_num, vars, inh, lab, mut, virt, ty, val_env, met_env, par_
         virt
       ];
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   var id = match[0];
@@ -77716,18 +79409,19 @@ function inheritance(self_type, env, ovf, concr_meths, warn_vals, loc, parent) {
                       exit = 1;
                     } else {
                       if (match$3.TAG === /* Tfield */5) {
-                        throw {
-                              MEL_EXN_ID: $$Error$9,
-                              _1: loc,
-                              _2: env,
-                              _3: {
-                                TAG: /* Field_type_mismatch */1,
-                                _0: "method",
-                                _1: match$3._0,
-                                _2: match$2.tl
-                              },
-                              Error: new Error()
-                            };
+                        throw new Error($$Error$9, {
+                                  cause: {
+                                    MEL_EXN_ID: $$Error$9,
+                                    _1: loc,
+                                    _2: env,
+                                    _3: {
+                                      TAG: /* Field_type_mismatch */1,
+                                      _0: "method",
+                                      _1: match$3._0,
+                                      _2: match$2.tl
+                                    }
+                                  }
+                                });
                       }
                       exit = 1;
                     }
@@ -77744,19 +79438,22 @@ function inheritance(self_type, env, ovf, concr_meths, warn_vals, loc, parent) {
               exit = 1;
             }
             if (exit === 1) {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      48280,
-                      12
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            48280,
+                            12
+                          ]
+                        }
+                      });
             }
             
           } else {
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }
         var over_meths = Curry._2(inter$1, cl_sig$1.csig_concr, concr_meths);
@@ -77795,17 +79492,18 @@ function inheritance(self_type, env, ovf, concr_meths, warn_vals, loc, parent) {
             }
             
           } else if (Curry._1(is_empty$1, over_meths) && Curry._1(is_empty$1, over_vals)) {
-            throw {
-                  MEL_EXN_ID: $$Error$9,
-                  _1: loc,
-                  _2: env,
-                  _3: {
-                    TAG: /* No_overriding */23,
-                    _0: "",
-                    _1: ""
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$9, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$9,
+                        _1: loc,
+                        _2: env,
+                        _3: {
+                          TAG: /* No_overriding */23,
+                          _0: "",
+                          _1: ""
+                        }
+                      }
+                    });
           }
           
         }
@@ -77818,16 +79516,17 @@ function inheritance(self_type, env, ovf, concr_meths, warn_vals, loc, parent) {
               ];
     case /* Cty_constr */0 :
     case /* Cty_arrow */2 :
-        throw {
-              MEL_EXN_ID: $$Error$9,
-              _1: loc,
-              _2: env,
-              _3: {
-                TAG: /* Structure_expected */2,
-                _0: parent
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$9, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$9,
+                    _1: loc,
+                    _2: env,
+                    _3: {
+                      TAG: /* Structure_expected */2,
+                      _0: parent
+                    }
+                  }
+                });
     
   }
 }
@@ -77843,20 +79542,23 @@ function virtual_method(val_env, meths, self_type, lab, priv, sty, loc) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: $$Error$9,
-            _1: loc,
-            _2: val_env,
-            _3: {
-              TAG: /* Field_type_mismatch */1,
-              _0: "method",
-              _1: lab,
-              _2: exn._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$9, {
+                cause: {
+                  MEL_EXN_ID: $$Error$9,
+                  _1: loc,
+                  _2: val_env,
+                  _3: {
+                    TAG: /* Field_type_mismatch */1,
+                    _0: "method",
+                    _1: lab,
+                    _2: exn._1
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return cty;
 }
@@ -77875,20 +79577,23 @@ function declare_method(val_env, meths, self_type, lab, priv, sty, loc) {
     catch (raw_exn){
       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
       if (exn.MEL_EXN_ID === Unify) {
-        throw {
-              MEL_EXN_ID: $$Error$9,
-              _1: loc,
-              _2: val_env,
-              _3: {
-                TAG: /* Field_type_mismatch */1,
-                _0: "method",
-                _1: lab,
-                _2: exn._1
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$9, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$9,
+                    _1: loc,
+                    _2: val_env,
+                    _3: {
+                      TAG: /* Field_type_mismatch */1,
+                      _0: "method",
+                      _1: lab,
+                      _2: exn._1
+                    }
+                  }
+                });
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   var sty$1 = force_poly(sty);
@@ -77932,18 +79637,21 @@ function type_constraint(val_env, sty, sty$p, loc) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: $$Error$9,
-            _1: loc,
-            _2: val_env,
-            _3: {
-              TAG: /* Unconsistent_constraint */0,
-              _0: exn._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$9, {
+                cause: {
+                  MEL_EXN_ID: $$Error$9,
+                  _1: loc,
+                  _2: val_env,
+                  _3: {
+                    TAG: /* Unconsistent_constraint */0,
+                    _0: exn._1
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return [
           cty,
@@ -77974,7 +79682,9 @@ function add_val(env, loc, lab, param, val_sig) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       virt$1 = virt;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   return Curry._3(Meths.add, lab, [
@@ -78009,18 +79719,21 @@ function class_signature$1(env, param) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: $$Error$9,
-            _1: sty.ptyp_loc,
-            _2: env,
-            _3: {
-              TAG: /* Pattern_type_clash */5,
-              _0: self_type
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$9, {
+                cause: {
+                  MEL_EXN_ID: $$Error$9,
+                  _1: sty.ptyp_loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* Pattern_type_clash */5,
+                    _0: self_type
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   warning_enter_scope(undefined);
   var match = Stdlib__List.fold_left((function (param, param$1) {
@@ -78165,11 +79878,12 @@ function class_signature$1(env, param) {
                         inher
                       ];
             case /* Pctf_extension */5 :
-                throw {
-                      MEL_EXN_ID: Error_forward$2,
-                      _1: error_of_extension(sparent._0),
-                      Error: new Error()
-                    };
+                throw new Error(Error_forward$2, {
+                          cause: {
+                            MEL_EXN_ID: Error_forward$2,
+                            _1: error_of_extension(sparent._0)
+                          }
+                        });
             
           }
         }), [
@@ -78214,32 +79928,34 @@ function class_type$3(env, scty) {
         var decl = match[1];
         var path = match[0];
         if (same(decl.clty_path, unbound_class)) {
-          throw {
-                MEL_EXN_ID: $$Error$9,
-                _1: scty.pcty_loc,
-                _2: env,
-                _3: {
-                  TAG: /* Unbound_class_type_2 */7,
-                  _0: lid.txt
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$9, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$9,
+                      _1: scty.pcty_loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Unbound_class_type_2 */7,
+                        _0: lid.txt
+                      }
+                    }
+                  });
         }
         var match$1 = instance_class(decl.clty_params, decl.clty_type);
         var params = match$1[0];
         if (Stdlib__List.length(params) !== Stdlib__List.length(styl)) {
-          throw {
-                MEL_EXN_ID: $$Error$9,
-                _1: scty.pcty_loc,
-                _2: env,
-                _3: {
-                  TAG: /* Parameter_arity_mismatch */11,
-                  _0: lid.txt,
-                  _1: Stdlib__List.length(params),
-                  _2: Stdlib__List.length(styl)
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$9, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$9,
+                      _1: scty.pcty_loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Parameter_arity_mismatch */11,
+                        _0: lid.txt,
+                        _1: Stdlib__List.length(params),
+                        _2: Stdlib__List.length(styl)
+                      }
+                    }
+                  });
         }
         var ctys = Stdlib__List.map2((function (sty, ty) {
                 var cty$p = transl_simple_type(env, false, sty);
@@ -78250,18 +79966,21 @@ function class_type$3(env, scty) {
                 catch (raw_exn){
                   var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                   if (exn.MEL_EXN_ID === Unify) {
-                    throw {
-                          MEL_EXN_ID: $$Error$9,
-                          _1: sty.ptyp_loc,
-                          _2: env,
-                          _3: {
-                            TAG: /* Parameter_mismatch */12,
-                            _0: exn._1
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$9, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$9,
+                                _1: sty.ptyp_loc,
+                                _2: env,
+                                _3: {
+                                  TAG: /* Parameter_mismatch */12,
+                                  _0: exn._1
+                                }
+                              }
+                            });
                   }
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
                 return cty$p;
               }), styl, params);
@@ -78307,11 +80026,12 @@ function class_type$3(env, scty) {
                     _2: clty
                   }, typ$2);
     case /* Pcty_extension */3 :
-        throw {
-              MEL_EXN_ID: Error_forward$2,
-              _1: error_of_extension(pcsig._0),
-              Error: new Error()
-            };
+        throw new Error(Error_forward$2, {
+                  cause: {
+                    MEL_EXN_ID: Error_forward$2,
+                    _1: error_of_extension(pcsig._0)
+                  }
+                });
     
   }
 }
@@ -78367,18 +80087,21 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Unify) {
-      throw {
-            MEL_EXN_ID: $$Error$9,
-            _1: spat.ppat_loc,
-            _2: val_env$1,
-            _3: {
-              TAG: /* Pattern_type_clash */5,
-              _0: public_self
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$9, {
+                cause: {
+                  MEL_EXN_ID: $$Error$9,
+                  _1: spat.ppat_loc,
+                  _2: val_env$1,
+                  _3: {
+                    TAG: /* Pattern_type_clash */5,
+                    _0: public_self
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   var get_methods = function (ty) {
     return flatten_fields(object_fields(expand_head(val_env$1, ty)))[0];
@@ -78390,15 +80113,16 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
               return unify$2(val_env$1, param[2], filter_method(val_env$1, param[0], k, self_type));
             }
             catch (exn){
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      48779,
-                      18
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            48779,
+                            18
+                          ]
+                        }
+                      });
             }
           }), get_methods(public_self));
   }
@@ -78581,17 +80305,18 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
                 }
                 var ovf$1 = styp._0;
                 if (Curry._2(mem$2, lab.txt, local_vals)) {
-                  throw {
-                        MEL_EXN_ID: $$Error$9,
-                        _1: loc,
-                        _2: val_env,
-                        _3: {
-                          TAG: /* Duplicate */24,
-                          _0: "instance variable",
-                          _1: lab.txt
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$9, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$9,
+                              _1: loc,
+                              _2: val_env,
+                              _3: {
+                                TAG: /* Duplicate */24,
+                                _0: "instance variable",
+                                _1: lab.txt
+                              }
+                            }
+                          });
                 }
                 if (Curry._2(mem$2, lab.txt, warn_vals)) {
                   if (ovf$1 === /* Fresh */1) {
@@ -78605,17 +80330,18 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
                   }
                   
                 } else if (ovf$1 === /* Override */0) {
-                  throw {
-                        MEL_EXN_ID: $$Error$9,
-                        _1: loc,
-                        _2: val_env,
-                        _3: {
-                          TAG: /* No_overriding */23,
-                          _0: "instance variable",
-                          _1: lab.txt
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$9, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$9,
+                              _1: loc,
+                              _2: val_env,
+                              _3: {
+                                TAG: /* No_overriding */23,
+                                _0: "instance variable",
+                                _1: lab.txt
+                              }
+                            }
+                          });
                 }
                 if (principal.contents) {
                   begin_def(undefined);
@@ -78630,22 +80356,29 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
                     var match$7 = exn._1;
                     if (match$7) {
                       if (match$7.tl) {
-                        throw exn;
+                        throw new Error(exn.MEL_EXN_ID, {
+                                  cause: exn
+                                });
                       }
-                      throw {
-                            MEL_EXN_ID: $$Error$9,
-                            _1: loc,
-                            _2: val_env,
-                            _3: {
-                              TAG: /* Make_nongen_seltype */17,
-                              _0: match$7.hd[0]
-                            },
-                            Error: new Error()
-                          };
+                      throw new Error($$Error$9, {
+                                cause: {
+                                  MEL_EXN_ID: $$Error$9,
+                                  _1: loc,
+                                  _2: val_env,
+                                  _3: {
+                                    TAG: /* Make_nongen_seltype */17,
+                                    _0: match$7.hd[0]
+                                  }
+                                }
+                              });
                     }
-                    throw exn;
+                    throw new Error(exn.MEL_EXN_ID, {
+                              cause: exn
+                            });
                   }
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
                 if (principal.contents) {
                   end_def(undefined);
@@ -78725,17 +80458,18 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
                 var expr$2;
                 expr$2 = match$10.TAG === /* Pexp_poly */28 ? expr$1 : Curry._4(Ast_helper_Exp.poly, expr$1.pexp_loc, undefined, expr$1, undefined);
                 if (Curry._2(mem$2, lab$1.txt, local_meths)) {
-                  throw {
-                        MEL_EXN_ID: $$Error$9,
-                        _1: loc,
-                        _2: val_env,
-                        _3: {
-                          TAG: /* Duplicate */24,
-                          _0: "method",
-                          _1: lab$1.txt
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$9, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$9,
+                              _1: loc,
+                              _2: val_env,
+                              _3: {
+                                TAG: /* Duplicate */24,
+                                _0: "method",
+                                _1: lab$1.txt
+                              }
+                            }
+                          });
                 }
                 if (Curry._2(mem$2, lab$1.txt, concr_meths)) {
                   if (ovf$2 === /* Fresh */1) {
@@ -78749,17 +80483,18 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
                   }
                   
                 } else if (ovf$2 === /* Override */0) {
-                  throw {
-                        MEL_EXN_ID: $$Error$9,
-                        _1: loc,
-                        _2: val_env,
-                        _3: {
-                          TAG: /* No_overriding */23,
-                          _0: "method",
-                          _1: lab$1.txt
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$9, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$9,
+                              _1: loc,
+                              _2: val_env,
+                              _3: {
+                                TAG: /* No_overriding */23,
+                                _0: "method",
+                                _1: lab$1.txt
+                              }
+                            }
+                          });
                 }
                 var match$11 = filter_self_method(val_env, lab$1.txt, priv, meths, self_type);
                 var ty$1 = match$11[1];
@@ -78776,15 +80511,16 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
                     }
                     var match$13 = repr(ty$1).desc;
                     if (typeof match$13 === "number") {
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              48681,
-                              17
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    48681,
+                                    17
+                                  ]
+                                }
+                              });
                     }
                     switch (match$13.TAG | 0) {
                       case /* Tvar */0 :
@@ -78802,45 +80538,50 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
                           unify$2(val_env, ty2, match$14[1]);
                           break;
                       default:
-                        throw {
-                              MEL_EXN_ID: "Assert_failure",
-                              _1: [
-                                "jscomp/test/ocaml_typedtree_test.ml",
-                                48681,
-                                17
-                              ],
-                              Error: new Error()
-                            };
+                        throw new Error("Assert_failure", {
+                                  cause: {
+                                    MEL_EXN_ID: "Assert_failure",
+                                    _1: [
+                                      "jscomp/test/ocaml_typedtree_test.ml",
+                                      48681,
+                                      17
+                                    ]
+                                  }
+                                });
                     }
                   } else {
-                    throw {
-                          MEL_EXN_ID: "Assert_failure",
-                          _1: [
-                            "jscomp/test/ocaml_typedtree_test.ml",
-                            48683,
-                            13
-                          ],
-                          Error: new Error()
-                        };
+                    throw new Error("Assert_failure", {
+                              cause: {
+                                MEL_EXN_ID: "Assert_failure",
+                                _1: [
+                                  "jscomp/test/ocaml_typedtree_test.ml",
+                                  48683,
+                                  13
+                                ]
+                              }
+                            });
                   }
                 }
                 catch (raw_exn$1){
                   var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
                   if (exn$1.MEL_EXN_ID === Unify) {
-                    throw {
-                          MEL_EXN_ID: $$Error$9,
-                          _1: loc,
-                          _2: val_env,
-                          _3: {
-                            TAG: /* Field_type_mismatch */1,
-                            _0: "method",
-                            _1: lab$1.txt,
-                            _2: exn$1._1
-                          },
-                          Error: new Error()
-                        };
+                    throw new Error($$Error$9, {
+                              cause: {
+                                MEL_EXN_ID: $$Error$9,
+                                _1: loc,
+                                _2: val_env,
+                                _3: {
+                                  TAG: /* Field_type_mismatch */1,
+                                  _0: "method",
+                                  _1: lab$1.txt,
+                                  _2: exn$1._1
+                                }
+                              }
+                            });
                   }
-                  throw exn$1;
+                  throw new Error(exn$1.MEL_EXN_ID, {
+                            cause: exn$1
+                          });
                 }
                 var meth_expr = make_method(self_loc, cl_num, expr$2);
                 var vars_local = vars.contents;
@@ -78980,11 +80721,12 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
                         local_vals
                       ];
             case /* Pcf_extension */6 :
-                throw {
-                      MEL_EXN_ID: Error_forward$2,
-                      _1: error_of_extension(expr._0),
-                      Error: new Error()
-                    };
+                throw new Error(Error_forward$2, {
+                          cause: {
+                            MEL_EXN_ID: Error_forward$2,
+                            _1: error_of_extension(expr._0)
+                          }
+                        });
             
           }
         }), [
@@ -79038,19 +80780,20 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
             }
           }), sign_csig_vars, /* [] */0);
     if (Caml_obj.caml_notequal(mets, /* [] */0) || Caml_obj.caml_notequal(vals, /* [] */0)) {
-      throw {
-            MEL_EXN_ID: $$Error$9,
-            _1: loc,
-            _2: val_env$1,
-            _3: {
-              TAG: /* Virtual_class */10,
-              _0: true,
-              _1: $$final,
-              _2: mets,
-              _3: vals
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$9, {
+                cause: {
+                  MEL_EXN_ID: $$Error$9,
+                  _1: loc,
+                  _2: val_env$1,
+                  _3: {
+                    TAG: /* Virtual_class */10,
+                    _0: true,
+                    _1: $$final,
+                    _2: mets,
+                    _3: vals
+                  }
+                }
+              });
     }
     var self_methods = Stdlib__List.fold_right((function (param, rem) {
             var kind = param[1];
@@ -79088,18 +80831,21 @@ function class_structure(cl_num, $$final, val_env, met_env, loc, param) {
     catch (raw_exn$1){
       var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
       if (exn$1.MEL_EXN_ID === Unify) {
-        throw {
-              MEL_EXN_ID: $$Error$9,
-              _1: loc,
-              _2: val_env$1,
-              _3: {
-                TAG: /* Final_self_clash */21,
-                _0: exn$1._1
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$9, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$9,
+                    _1: loc,
+                    _2: val_env$1,
+                    _3: {
+                      TAG: /* Final_self_clash */21,
+                      _0: exn$1._1
+                    }
+                  }
+                });
       }
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
   }
   if (principal.contents) {
@@ -79163,16 +80909,17 @@ function class_expr(cl_num, val_env, met_env, _scl) {
           var decl = match[1];
           var path = match[0];
           if (same(decl.cty_path, unbound_class)) {
-            throw {
-                  MEL_EXN_ID: $$Error$9,
-                  _1: scl.pcl_loc,
-                  _2: val_env,
-                  _3: {
-                    TAG: /* Unbound_class_2 */6,
-                    _0: lid.txt
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$9, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$9,
+                        _1: scl.pcl_loc,
+                        _2: val_env,
+                        _3: {
+                          TAG: /* Unbound_class_2 */6,
+                          _0: lid.txt
+                        }
+                      }
+                    });
           }
           var tyl = Stdlib__List.map((function (sty) {
                   return transl_simple_type(val_env, false, sty);
@@ -79182,18 +80929,19 @@ function class_expr(cl_num, val_env, met_env, _scl) {
           var params = match$1[0];
           var clty$p = abbreviate_class_type(path, params, clty);
           if (Stdlib__List.length(params) !== Stdlib__List.length(tyl)) {
-            throw {
-                  MEL_EXN_ID: $$Error$9,
-                  _1: scl.pcl_loc,
-                  _2: val_env,
-                  _3: {
-                    TAG: /* Parameter_arity_mismatch */11,
-                    _0: lid.txt,
-                    _1: Stdlib__List.length(params),
-                    _2: Stdlib__List.length(tyl)
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$9, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$9,
+                        _1: scl.pcl_loc,
+                        _2: val_env,
+                        _3: {
+                          TAG: /* Parameter_arity_mismatch */11,
+                          _0: lid.txt,
+                          _1: Stdlib__List.length(params),
+                          _2: Stdlib__List.length(tyl)
+                        }
+                      }
+                    });
           }
           Stdlib__List.iter2((function (cty$p, ty) {
                   var ty$p = cty$p.ctyp_type;
@@ -79203,18 +80951,21 @@ function class_expr(cl_num, val_env, met_env, _scl) {
                   catch (raw_exn){
                     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
                     if (exn.MEL_EXN_ID === Unify) {
-                      throw {
-                            MEL_EXN_ID: $$Error$9,
-                            _1: cty$p.ctyp_loc,
-                            _2: val_env,
-                            _3: {
-                              TAG: /* Parameter_mismatch */12,
-                              _0: exn._1
-                            },
-                            Error: new Error()
-                          };
+                      throw new Error($$Error$9, {
+                                cause: {
+                                  MEL_EXN_ID: $$Error$9,
+                                  _1: cty$p.ctyp_loc,
+                                  _2: val_env,
+                                  _3: {
+                                    TAG: /* Parameter_mismatch */12,
+                                    _0: exn._1
+                                  }
+                                }
+                              });
                     }
-                    throw exn;
+                    throw new Error(exn.MEL_EXN_ID, {
+                              cause: exn
+                            });
                   }
                 }), tyl, params);
           var cl = rc({
@@ -79496,32 +81247,34 @@ function class_expr(cl_num, val_env, met_env, _scl) {
                             if (ignore_labels && !is_optional(l)) {
                               if (sargs) {
                                 var match$1 = sargs.hd;
-                                throw {
-                                      MEL_EXN_ID: $$Error$9,
-                                      _1: match$1[1].pexp_loc,
-                                      _2: val_env,
-                                      _3: {
-                                        TAG: /* Apply_wrong_label */4,
-                                        _0: match$1[0]
-                                      },
-                                      Error: new Error()
-                                    };
+                                throw new Error($$Error$9, {
+                                          cause: {
+                                            MEL_EXN_ID: $$Error$9,
+                                            _1: match$1[1].pexp_loc,
+                                            _2: val_env,
+                                            _3: {
+                                              TAG: /* Apply_wrong_label */4,
+                                              _0: match$1[0]
+                                            }
+                                          }
+                                        });
                               }
                               if (more_sargs) {
                                 var match$2 = more_sargs.hd;
                                 var sarg0 = match$2[1];
                                 var l$p = match$2[0];
                                 if (l !== l$p && l$p !== "") {
-                                  throw {
-                                        MEL_EXN_ID: $$Error$9,
-                                        _1: sarg0.pexp_loc,
-                                        _2: val_env,
-                                        _3: {
-                                          TAG: /* Apply_wrong_label */4,
-                                          _0: l$p
-                                        },
-                                        Error: new Error()
-                                      };
+                                  throw new Error($$Error$9, {
+                                            cause: {
+                                              MEL_EXN_ID: $$Error$9,
+                                              _1: sarg0.pexp_loc,
+                                              _2: val_env,
+                                              _3: {
+                                                TAG: /* Apply_wrong_label */4,
+                                                _0: l$p
+                                              }
+                                            }
+                                          });
                                 }
                                 match = [
                                   /* [] */0,
@@ -79529,15 +81282,16 @@ function class_expr(cl_num, val_env, met_env, _scl) {
                                   type_argument(val_env, sarg0, ty, ty0)
                                 ];
                               } else {
-                                throw {
-                                      MEL_EXN_ID: "Assert_failure",
-                                      _1: [
-                                        "jscomp/test/ocaml_typedtree_test.ml",
-                                        49036,
-                                        20
-                                      ],
-                                      Error: new Error()
-                                    };
+                                throw new Error("Assert_failure", {
+                                          cause: {
+                                            MEL_EXN_ID: "Assert_failure",
+                                            _1: [
+                                              "jscomp/test/ocaml_typedtree_test.ml",
+                                              49036,
+                                              20
+                                            ]
+                                          }
+                                        });
                               }
                             } else {
                               try {
@@ -79562,7 +81316,9 @@ function class_expr(cl_num, val_env, met_env, _scl) {
                                       match$5[3]
                                     ];
                                   } else {
-                                    throw exn;
+                                    throw new Error(exn.MEL_EXN_ID, {
+                                              cause: exn
+                                            });
                                   }
                                 }
                                 var sarg0$1 = match$3[1];
@@ -79597,7 +81353,9 @@ function class_expr(cl_num, val_env, met_env, _scl) {
                                     is_optional(l) && (Stdlib__List.mem_assoc("", sargs) || Stdlib__List.mem_assoc("", more_sargs)) ? option_none(ty0, none) : undefined
                                   ];
                                 } else {
-                                  throw exn$1;
+                                  throw new Error(exn$1.MEL_EXN_ID, {
+                                            cause: exn$1
+                                          });
                                 }
                               }
                             }
@@ -79646,27 +81404,29 @@ function class_expr(cl_num, val_env, met_env, _scl) {
               }
               if (Caml_obj.caml_notequal(omitted, /* [] */0)) {
                 var match$7 = match$6.hd;
-                throw {
-                      MEL_EXN_ID: $$Error$9,
-                      _1: match$7[1].pexp_loc,
-                      _2: val_env,
-                      _3: {
-                        TAG: /* Apply_wrong_label */4,
-                        _0: match$7[0]
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$9, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$9,
+                            _1: match$7[1].pexp_loc,
+                            _2: val_env,
+                            _3: {
+                              TAG: /* Apply_wrong_label */4,
+                              _0: match$7[0]
+                            }
+                          }
+                        });
               }
-              throw {
-                    MEL_EXN_ID: $$Error$9,
-                    _1: cl$2.cl_loc,
-                    _2: val_env,
-                    _3: {
-                      TAG: /* Cannot_apply */3,
-                      _0: cl$2.cl_type
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$9, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$9,
+                          _1: cl$2.cl_loc,
+                          _2: val_env,
+                          _3: {
+                            TAG: /* Cannot_apply */3,
+                            _0: cl$2.cl_type
+                          }
+                        }
+                      });
             };
           }
           }(cl$2,ignore_labels));
@@ -79696,22 +81456,29 @@ function class_expr(cl_num, val_env, met_env, _scl) {
               var match$8 = exn._1;
               if (match$8) {
                 if (match$8.tl) {
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: $$Error$9,
-                      _1: scl.pcl_loc,
-                      _2: val_env,
-                      _3: {
-                        TAG: /* Make_nongen_seltype */17,
-                        _0: match$8.hd[0]
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$9, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$9,
+                            _1: scl.pcl_loc,
+                            _2: val_env,
+                            _3: {
+                              TAG: /* Make_nongen_seltype */17,
+                              _0: match$8.hd[0]
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           var val_env$1 = match$7[1];
           var defs = match$7[0];
@@ -79806,16 +81573,17 @@ function class_expr(cl_num, val_env, met_env, _scl) {
           limited_generalize$1(row_variable(repr(signature_of_class_type(clty$1.cltyp_type).csig_self)), clty$1.cltyp_type);
           var error = class_types(val_env, cl$4.cl_type, clty$1.cltyp_type);
           if (error) {
-            throw {
-                  MEL_EXN_ID: $$Error$9,
-                  _1: cl$4.cl_loc,
-                  _2: val_env,
-                  _3: {
-                    TAG: /* Class_match_failure */14,
-                    _0: error
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$9, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$9,
+                        _1: cl$4.cl_loc,
+                        _2: val_env,
+                        _3: {
+                          TAG: /* Class_match_failure */14,
+                          _0: error
+                        }
+                      }
+                    });
           }
           var match$10 = extract_constraints(clty$1.cltyp_type);
           return rc({
@@ -79833,11 +81601,12 @@ function class_expr(cl_num, val_env, met_env, _scl) {
                       cl_attributes: scl.pcl_attributes
                     });
       case /* Pcl_extension */6 :
-          throw {
-                MEL_EXN_ID: Error_forward$2,
-                _1: error_of_extension(cl_str._0),
-                Error: new Error()
-              };
+          throw new Error(Error_forward$2, {
+                    cause: {
+                      MEL_EXN_ID: Error_forward$2,
+                      _1: error_of_extension(cl_str._0)
+                    }
+                  });
       
     }
   };
@@ -80056,15 +81825,18 @@ function type_classes(define_class, approx, kind, env, cls) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Already_bound) {
-                throw {
-                      MEL_EXN_ID: $$Error$9,
-                      _1: sty.ptyp_loc,
-                      _2: env,
-                      _3: /* Repeated_parameter */0,
-                      Error: new Error()
-                    };
+                throw new Error($$Error$9, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$9,
+                            _1: sty.ptyp_loc,
+                            _2: env,
+                            _3: /* Repeated_parameter */0
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           };
           var ci_params = Stdlib__List.map(make_param, cl.pci_params);
@@ -80092,7 +81864,9 @@ function type_classes(define_class, approx, kind, env, cls) {
           }
           catch (exn){
             self_coercion.contents = /* [] */0;
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           var typ = match[1];
           end_def(undefined);
@@ -80129,23 +81903,26 @@ function type_classes(define_class, approx, kind, env, cls) {
           catch (raw_exn){
             var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn$1.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$9,
-                    _1: cl.pci_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Bad_parameters */13,
-                      _0: obj_id,
-                      _1: constr,
-                      _2: newconstr({
-                            TAG: /* Pident */0,
-                            _0: obj_id
-                          }, obj_params$p)
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$9, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$9,
+                          _1: cl.pci_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Bad_parameters */13,
+                            _0: obj_id,
+                            _1: constr,
+                            _2: newconstr({
+                                  TAG: /* Pident */0,
+                                  _0: obj_id
+                                }, obj_params$p)
+                          }
+                        }
+                      });
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
           try {
             unify$2(env, ty, constr);
@@ -80153,20 +81930,23 @@ function type_classes(define_class, approx, kind, env, cls) {
           catch (raw_exn$1){
             var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
             if (exn$2.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$9,
-                    _1: cl.pci_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Abbrev_type_clash */8,
-                      _0: constr,
-                      _1: ty,
-                      _2: expand_head(env, constr)
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$9, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$9,
+                          _1: cl.pci_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Abbrev_type_clash */8,
+                            _0: constr,
+                            _1: ty,
+                            _2: expand_head(env, constr)
+                          }
+                        }
+                      });
             }
-            throw exn$2;
+            throw new Error(exn$2.MEL_EXN_ID, {
+                      cause: exn$2
+                    });
           }
           var match$3 = instance_class(params, typ);
           var cl_params$p = match$3[0];
@@ -80181,26 +81961,29 @@ function type_classes(define_class, approx, kind, env, cls) {
           catch (raw_exn$2){
             var exn$3 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
             if (exn$3.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$9,
-                    _1: cl.pci_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Bad_parameters */13,
-                      _0: cl_id,
-                      _1: newconstr({
-                            TAG: /* Pident */0,
-                            _0: cl_id
-                          }, cl_params),
-                      _2: newconstr({
-                            TAG: /* Pident */0,
-                            _0: cl_id
-                          }, cl_params$p)
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$9, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$9,
+                          _1: cl.pci_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Bad_parameters */13,
+                            _0: cl_id,
+                            _1: newconstr({
+                                  TAG: /* Pident */0,
+                                  _0: cl_id
+                                }, cl_params),
+                            _2: newconstr({
+                                  TAG: /* Pident */0,
+                                  _0: cl_id
+                                }, cl_params$p)
+                          }
+                        }
+                      });
             }
-            throw exn$3;
+            throw new Error(exn$3.MEL_EXN_ID, {
+                      cause: exn$3
+                    });
           }
           try {
             unify$2(env, ty$1, cl_ty);
@@ -80212,20 +81995,23 @@ function type_classes(define_class, approx, kind, env, cls) {
                     TAG: /* Pident */0,
                     _0: cl_id
                   }, params);
-              throw {
-                    MEL_EXN_ID: $$Error$9,
-                    _1: cl.pci_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Abbrev_type_clash */8,
-                      _0: constr$1,
-                      _1: ty$1,
-                      _2: cl_ty
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$9, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$9,
+                          _1: cl.pci_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Abbrev_type_clash */8,
+                            _0: constr$1,
+                            _1: ty$1,
+                            _2: cl_ty
+                          }
+                        }
+                      });
             }
-            throw exn$4;
+            throw new Error(exn$4.MEL_EXN_ID, {
+                      cause: exn$4
+                    });
           }
           try {
             unify$2(env, constructor_type(constr, obj_type), instance(undefined, env, constr_type));
@@ -80233,19 +82019,22 @@ function type_classes(define_class, approx, kind, env, cls) {
           catch (raw_exn$4){
             var exn$5 = Caml_js_exceptions.internalToOCamlException(raw_exn$4);
             if (exn$5.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$9,
-                    _1: cl.pci_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Constructor_type_mismatch */9,
-                      _0: cl.pci_name.txt,
-                      _1: exn$5._1
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$9, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$9,
+                          _1: cl.pci_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Constructor_type_mismatch */9,
+                            _0: cl.pci_name.txt,
+                            _1: exn$5._1
+                          }
+                        }
+                      });
             }
-            throw exn$5;
+            throw new Error(exn$5.MEL_EXN_ID, {
+                      cause: exn$5
+                    });
           }
           var cty_variance = Stdlib__List.map((function (param) {
                   return Types_Variance.full;
@@ -80294,19 +82083,20 @@ function type_classes(define_class, approx, kind, env, cls) {
                     }
                   }), sign.csig_vars, /* [] */0);
             if (Caml_obj.caml_notequal(mets, /* [] */0) || Caml_obj.caml_notequal(vals, /* [] */0)) {
-              throw {
-                    MEL_EXN_ID: $$Error$9,
-                    _1: cl.pci_loc,
-                    _2: env$1,
-                    _3: {
-                      TAG: /* Virtual_class */10,
-                      _0: define_class,
-                      _1: false,
-                      _2: mets,
-                      _3: vals
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$9, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$9,
+                          _1: cl.pci_loc,
+                          _2: env$1,
+                          _3: {
+                            TAG: /* Virtual_class */10,
+                            _0: define_class,
+                            _1: false,
+                            _2: mets,
+                            _3: vals
+                          }
+                        }
+                      });
             }
             
           }
@@ -80430,20 +82220,23 @@ function type_classes(define_class, approx, kind, env, cls) {
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$9,
-                    _1: cl.pci_loc,
-                    _2: env$1,
-                    _3: {
-                      TAG: /* Non_collapsable_conjunction */20,
-                      _0: id,
-                      _1: clty,
-                      _2: exn._1
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$9, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$9,
+                          _1: cl.pci_loc,
+                          _2: env$1,
+                          _3: {
+                            TAG: /* Non_collapsable_conjunction */20,
+                            _0: id,
+                            _1: clty,
+                            _2: exn._1
+                          }
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           Stdlib__List.iter(generalize, clty.cty_params);
           generalize_class_type(generalize, clty.cty_type);
@@ -80453,17 +82246,18 @@ function type_classes(define_class, approx, kind, env, cls) {
           Stdlib__List.iter(generalize, cl_abbr.type_params);
           may(generalize, cl_abbr.type_manifest);
           if (!closed_class$1(clty)) {
-            throw {
-                  MEL_EXN_ID: $$Error$9,
-                  _1: cl.pci_loc,
-                  _2: env$1,
-                  _3: {
-                    TAG: /* Non_generalizable_class */18,
-                    _0: id,
-                    _1: clty
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$9, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$9,
+                        _1: cl.pci_loc,
+                        _2: env$1,
+                        _3: {
+                          TAG: /* Non_generalizable_class */18,
+                          _0: id,
+                          _1: clty
+                        }
+                      }
+                    });
           }
           var reason = closed_class(clty.cty_params, signature_of_class_type(clty.cty_type));
           if (reason !== undefined) {
@@ -80472,17 +82266,18 @@ function type_classes(define_class, approx, kind, env, cls) {
                 }) : (function (ppf) {
                   cltype_declaration$1(id, ppf, cltydef);
                 });
-            throw {
-                  MEL_EXN_ID: $$Error$9,
-                  _1: cl.pci_loc,
-                  _2: env$1,
-                  _3: {
-                    TAG: /* Unbound_type_var */16,
-                    _0: printer,
-                    _1: reason
-                  },
-                  Error: new Error()
-                };
+            throw new Error($$Error$9, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$9,
+                        _1: cl.pci_loc,
+                        _2: env$1,
+                        _3: {
+                          TAG: /* Unbound_type_var */16,
+                          _0: printer,
+                          _1: reason
+                        }
+                      }
+                    });
           }
           return [
                   id,
@@ -80541,26 +82336,28 @@ function type_classes(define_class, approx, kind, env, cls) {
                   match$4[1]
                 ];
               } else {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        49581,
-                        15
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              49581,
+                              15
+                            ]
+                          }
+                        });
               }
             } else {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      49581,
-                      15
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            49581,
+                            15
+                          ]
+                        }
+                      });
             }
             var obj_ty = match$2[1];
             var cl_ty = match$2[0];
@@ -80570,31 +82367,35 @@ function type_classes(define_class, approx, kind, env, cls) {
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Subtype) {
-                throw {
-                      MEL_EXN_ID: $$Error$7,
-                      _1: loc,
-                      _2: env$2,
-                      _3: {
-                        TAG: /* Not_subtype */23,
-                        _0: exn._1,
-                        _1: exn._2
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$7, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$7,
+                            _1: loc,
+                            _2: env$2,
+                            _3: {
+                              TAG: /* Not_subtype */23,
+                              _0: exn._1,
+                              _1: exn._2
+                            }
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
             if (!opened_object(cl_ty)) {
-              throw {
-                    MEL_EXN_ID: $$Error$9,
-                    _1: loc,
-                    _2: env$2,
-                    _3: {
-                      TAG: /* Cannot_coerce_self */19,
-                      _0: obj_ty
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$9, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$9,
+                          _1: loc,
+                          _2: env$2,
+                          _3: {
+                            TAG: /* Cannot_coerce_self */19,
+                            _0: obj_ty
+                          }
+                        }
+                      });
             }
             
           }
@@ -80687,15 +82488,16 @@ function unify_parents_struct(env, ty, st) {
                       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
                         return ;
                       }
-                      throw {
-                            MEL_EXN_ID: "Assert_failure",
-                            _1: [
-                              "jscomp/test/ocaml_typedtree_test.ml",
-                              49658,
-                              15
-                            ],
-                            Error: new Error()
-                          };
+                      throw new Error("Assert_failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Assert_failure",
+                                  _1: [
+                                    "jscomp/test/ocaml_typedtree_test.ml",
+                                    49658,
+                                    15
+                                  ]
+                                }
+                              });
                     }
                 case /* Tcl_structure */1 :
                     return unify_parents_struct(env, ty, st._0);
@@ -82201,15 +84003,16 @@ function path_concat(head, p) {
                 _2: p._2
               };
     case /* Papply */2 :
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/ocaml_typedtree_test.ml",
-                50016,
-                16
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/ocaml_typedtree_test.ml",
+                      50016,
+                      16
+                    ]
+                  }
+                });
     
   }
 }
@@ -82219,13 +84022,14 @@ function extract_sig(env, loc, mty) {
   if (sg.TAG === /* Mty_signature */1) {
     return sg._0;
   }
-  throw {
-        MEL_EXN_ID: $$Error$10,
-        _1: loc,
-        _2: env,
-        _3: /* Signature_expected */0,
-        Error: new Error()
-      };
+  throw new Error($$Error$10, {
+            cause: {
+              MEL_EXN_ID: $$Error$10,
+              _1: loc,
+              _2: env,
+              _3: /* Signature_expected */0
+            }
+          });
 }
 
 function extract_sig_open(env, loc, mty) {
@@ -82233,16 +84037,17 @@ function extract_sig_open(env, loc, mty) {
   if (sg.TAG === /* Mty_signature */1) {
     return sg._0;
   }
-  throw {
-        MEL_EXN_ID: $$Error$10,
-        _1: loc,
-        _2: env,
-        _3: {
-          TAG: /* Structure_expected */3,
-          _0: mty
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$10, {
+            cause: {
+              MEL_EXN_ID: $$Error$10,
+              _1: loc,
+              _2: env,
+              _3: {
+                TAG: /* Structure_expected */3,
+                _0: mty
+              }
+            }
+          });
 }
 
 function type_open_(toplevel, ovf, env, loc, lid) {
@@ -82278,15 +84083,16 @@ function type_open$1(toplevel, env, sod) {
 
 var type_module_type_of_fwd = {
   contents: (function (env, m) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/ocaml_typedtree_test.ml",
-              50061,
-              22
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/ocaml_typedtree_test.ml",
+                    50061,
+                    22
+                  ]
+                }
+              });
     })
 };
 
@@ -82723,16 +84529,17 @@ function merge_constraint(initial_env, loc, sg, constr) {
                 }
               ];
       }
-      throw {
-            MEL_EXN_ID: $$Error$10,
-            _1: loc,
-            _2: env,
-            _3: {
-              TAG: /* With_no_component */4,
-              _0: lid.txt
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$10, {
+                cause: {
+                  MEL_EXN_ID: $$Error$10,
+                  _1: loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* With_no_component */4,
+                    _0: lid.txt
+                  }
+                }
+              });
     };
   };
   try {
@@ -82753,15 +84560,16 @@ function merge_constraint(initial_env, loc, sg, constr) {
             if (id !== undefined) {
               id$1 = id;
             } else {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      50208,
-                      38
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            50208,
+                            38
+                          ]
+                        }
+                      });
             }
             var lid$1;
             try {
@@ -82769,10 +84577,11 @@ function merge_constraint(initial_env, loc, sg, constr) {
               if (match$1 !== undefined) {
                 var match$2 = match$1.ptyp_desc;
                 if (typeof match$2 === "number") {
-                  throw {
-                        MEL_EXN_ID: Stdlib.Exit,
-                        Error: new Error()
-                      };
+                  throw new Error(Stdlib.Exit, {
+                            cause: {
+                              MEL_EXN_ID: Stdlib.Exit
+                            }
+                          });
                 }
                 if (match$2.TAG === /* Ptyp_constr */3) {
                   var stl = match$2._1;
@@ -82780,71 +84589,82 @@ function merge_constraint(initial_env, loc, sg, constr) {
                     Stdlib__List.iter2((function (x, param) {
                             var sx = x.ptyp_desc;
                             if (typeof sx === "number") {
-                              throw {
-                                    MEL_EXN_ID: Stdlib.Exit,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Stdlib.Exit, {
+                                        cause: {
+                                          MEL_EXN_ID: Stdlib.Exit
+                                        }
+                                      });
                             }
                             if (sx.TAG === /* Ptyp_var */0) {
                               var sy = param[0].ptyp_desc;
                               if (typeof sy === "number") {
-                                throw {
-                                      MEL_EXN_ID: Stdlib.Exit,
-                                      Error: new Error()
-                                    };
+                                throw new Error(Stdlib.Exit, {
+                                          cause: {
+                                            MEL_EXN_ID: Stdlib.Exit
+                                          }
+                                        });
                               }
                               if (sy.TAG === /* Ptyp_var */0) {
                                 if (sx._0 === sy._0) {
                                   return ;
                                 }
-                                throw {
-                                      MEL_EXN_ID: Stdlib.Exit,
-                                      Error: new Error()
-                                    };
+                                throw new Error(Stdlib.Exit, {
+                                          cause: {
+                                            MEL_EXN_ID: Stdlib.Exit
+                                          }
+                                        });
                               }
-                              throw {
-                                    MEL_EXN_ID: Stdlib.Exit,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Stdlib.Exit, {
+                                        cause: {
+                                          MEL_EXN_ID: Stdlib.Exit
+                                        }
+                                      });
                             } else {
-                              throw {
-                                    MEL_EXN_ID: Stdlib.Exit,
-                                    Error: new Error()
-                                  };
+                              throw new Error(Stdlib.Exit, {
+                                        cause: {
+                                          MEL_EXN_ID: Stdlib.Exit
+                                        }
+                                      });
                             }
                           }), stl, sdecl.ptype_params);
                     lid$1 = match$2._0;
                   } else {
-                    throw {
-                          MEL_EXN_ID: Stdlib.Exit,
-                          Error: new Error()
-                        };
+                    throw new Error(Stdlib.Exit, {
+                              cause: {
+                                MEL_EXN_ID: Stdlib.Exit
+                              }
+                            });
                   }
                 } else {
-                  throw {
-                        MEL_EXN_ID: Stdlib.Exit,
-                        Error: new Error()
-                      };
+                  throw new Error(Stdlib.Exit, {
+                            cause: {
+                              MEL_EXN_ID: Stdlib.Exit
+                            }
+                          });
                 }
               } else {
-                throw {
-                      MEL_EXN_ID: Stdlib.Exit,
-                      Error: new Error()
-                    };
+                throw new Error(Stdlib.Exit, {
+                          cause: {
+                            MEL_EXN_ID: Stdlib.Exit
+                          }
+                        });
               }
             }
             catch (raw_exn){
               var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
               if (exn.MEL_EXN_ID === Stdlib.Exit) {
-                throw {
-                      MEL_EXN_ID: $$Error$10,
-                      _1: sdecl.ptype_loc,
-                      _2: initial_env,
-                      _3: /* With_need_typeconstr */2,
-                      Error: new Error()
-                    };
+                throw new Error($$Error$10, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$10,
+                            _1: sdecl.ptype_loc,
+                            _2: initial_env,
+                            _3: /* With_need_typeconstr */2
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
             var match$3;
             try {
@@ -82853,17 +84673,20 @@ function merge_constraint(initial_env, loc, sg, constr) {
             catch (raw_exn$1){
               var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
               if (exn$1.MEL_EXN_ID === Stdlib.Not_found) {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/ocaml_typedtree_test.ml",
-                        50225,
-                        68
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/ocaml_typedtree_test.ml",
+                              50225,
+                              68
+                            ]
+                          }
+                        });
               }
-              throw exn$1;
+              throw new Error(exn$1.MEL_EXN_ID, {
+                        cause: exn$1
+                      });
             }
             var sub = add_type(id$1, match$3[0], identity);
             sg$2 = signature$2(sub, sg$1);
@@ -82874,15 +84697,16 @@ function merge_constraint(initial_env, loc, sg, constr) {
             if (id$2 !== undefined) {
               id$3 = id$2;
             } else {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/ocaml_typedtree_test.ml",
-                      50231,
-                      38
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/ocaml_typedtree_test.ml",
+                            50231,
+                            38
+                          ]
+                        }
+                      });
             }
             var path = lookup_module$1(undefined, initial_env, loc, constr._1.txt);
             var sub$1 = add_module(id$3, path, identity);
@@ -82901,19 +84725,22 @@ function merge_constraint(initial_env, loc, sg, constr) {
   catch (raw_exn$2){
     var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
     if (exn$2.MEL_EXN_ID === $$Error$5) {
-      throw {
-            MEL_EXN_ID: $$Error$10,
-            _1: loc,
-            _2: initial_env,
-            _3: {
-              TAG: /* With_mismatch */5,
-              _0: lid.txt,
-              _1: exn$2._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$10, {
+                cause: {
+                  MEL_EXN_ID: $$Error$10,
+                  _1: loc,
+                  _2: initial_env,
+                  _3: {
+                    TAG: /* With_mismatch */5,
+                    _0: lid.txt,
+                    _1: exn$2._1
+                  }
+                }
+              });
     }
-    throw exn$2;
+    throw new Error(exn$2.MEL_EXN_ID, {
+              cause: exn$2
+            });
   }
 }
 
@@ -83015,11 +84842,12 @@ function approx_modtype(env, _smty) {
       case /* Pmty_typeof */4 :
           return Curry._2(type_module_type_of_fwd.contents, env, lid._0)[1];
       case /* Pmty_extension */5 :
-          throw {
-                MEL_EXN_ID: Error_forward$3,
-                _1: error_of_extension(lid._0),
-                Error: new Error()
-              };
+          throw new Error(Error_forward$3, {
+                    cause: {
+                      MEL_EXN_ID: Error_forward$3,
+                      _1: error_of_extension(lid._0)
+                    }
+                  });
       case /* Pmty_alias */6 :
           var path = lookup_module$1(undefined, env, smty.pmty_loc, lid._0.txt);
           return {
@@ -83230,17 +85058,19 @@ function bal$12(l, v, r) {
       if (lr) {
         return create$13(create$13(ll, lv, lr.l), lr.v, create$13(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -83260,17 +85090,19 @@ function bal$12(l, v, r) {
     if (rl) {
       return create$13(create$13(l, v, rl.l), rl.v, create$13(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add$14(x, t) {
@@ -83322,17 +85154,18 @@ function mem$7(x, _param) {
 
 function check(cl, loc, set_ref, name) {
   if (Curry._2(mem$7, name, set_ref.contents)) {
-    throw {
-          MEL_EXN_ID: $$Error$10,
-          _1: loc,
-          _2: empty,
-          _3: {
-            TAG: /* Repeated_name */6,
-            _0: cl,
-            _1: name
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$10, {
+              cause: {
+                MEL_EXN_ID: $$Error$10,
+                _1: loc,
+                _2: empty,
+                _3: {
+                  TAG: /* Repeated_name */6,
+                  _0: cl,
+                  _1: name
+                }
+              }
+            });
   }
   set_ref.contents = Curry._2(add$14, name, set_ref.contents);
 }
@@ -83581,11 +85414,12 @@ function transl_modtype$1(env, smty) {
                     _0: match$2[0]
                   }, match$2[1], env, loc, smty.pmty_attributes);
     case /* Pmty_extension */5 :
-        throw {
-              MEL_EXN_ID: Error_forward$3,
-              _1: error_of_extension(lid._0),
-              Error: new Error()
-            };
+        throw new Error(Error_forward$3, {
+                  cause: {
+                    MEL_EXN_ID: Error_forward$3,
+                    _1: error_of_extension(lid._0)
+                  }
+                });
     case /* Pmty_alias */6 :
         var lid$2 = lid._0;
         var path$1 = transl_module_alias(loc, env, lid$2.txt);
@@ -83999,11 +85833,12 @@ function transl_signature(env, sg) {
                   match$21[2]
                 ];
       case /* Psig_extension */12 :
-          throw {
-                MEL_EXN_ID: Error_forward$3,
-                _1: error_of_extension(sdesc._0),
-                Error: new Error()
-              };
+          throw new Error(Error_forward$3, {
+                    cause: {
+                      MEL_EXN_ID: Error_forward$3,
+                      _1: error_of_extension(sdesc._0)
+                    }
+                  });
       
     }
   };
@@ -84226,18 +86061,20 @@ function path_of_module(_mexp) {
                     _1: path_of_module(match._1)
                   };
           }
-          throw {
-                MEL_EXN_ID: Not_a_path,
-                Error: new Error()
-              };
+          throw new Error(Not_a_path, {
+                    cause: {
+                      MEL_EXN_ID: Not_a_path
+                    }
+                  });
       case /* Tmod_constraint */4 :
           _mexp = match._0;
           continue ;
       default:
-        throw {
-              MEL_EXN_ID: Not_a_path,
-              Error: new Error()
-            };
+        throw new Error(Not_a_path, {
+                  cause: {
+                    MEL_EXN_ID: Not_a_path
+                  }
+                });
     }
   };
 }
@@ -84251,7 +86088,9 @@ function path_of_module$1(mexp) {
     if (exn.MEL_EXN_ID === Not_a_path) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -84383,18 +86222,21 @@ function check_recmodule_inclusion(env, bindings) {
       catch (raw_exn){
         var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
         if (exn.MEL_EXN_ID === $$Error$5) {
-          throw {
-                MEL_EXN_ID: $$Error$10,
-                _1: modl.mod_loc,
-                _2: env$1,
-                _3: {
-                  TAG: /* Not_included */1,
-                  _0: exn._1
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$10, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$10,
+                      _1: modl.mod_loc,
+                      _2: env$1,
+                      _3: {
+                        TAG: /* Not_included */1,
+                        _0: exn._1
+                      }
+                    }
+                  });
         }
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
       var modl$p_mod_desc = {
         TAG: /* Tmod_constraint */4,
@@ -84542,13 +86384,14 @@ function modtype_of_package(env, loc, p, nl, tl) {
                 _0: p
               };
       }
-      throw {
-            MEL_EXN_ID: $$Error$10,
-            _1: loc,
-            _2: env,
-            _3: /* Signature_expected */0,
-            Error: new Error()
-          };
+      throw new Error($$Error$10, {
+                cause: {
+                  MEL_EXN_ID: $$Error$10,
+                  _1: loc,
+                  _2: env,
+                  _3: /* Signature_expected */0
+                }
+              });
     }
     
   }
@@ -84559,15 +86402,18 @@ function modtype_of_package(env, loc, p, nl, tl) {
         TAG: /* Unbound_modtype */22,
         _0: lid_of_path(undefined, p)
       };
-      throw {
-            MEL_EXN_ID: $$Error$6,
-            _1: loc,
-            _2: env,
-            _3: error,
-            Error: new Error()
-          };
+      throw new Error($$Error$6, {
+                cause: {
+                  MEL_EXN_ID: $$Error$6,
+                  _1: loc,
+                  _2: env,
+                  _3: error
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -84589,7 +86435,9 @@ function package_subtype$1(env, p1, nl1, tl1, p2, nl2, tl2) {
     if (exn.MEL_EXN_ID === $$Error$5) {
       return false;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -84603,18 +86451,21 @@ function wrap_constraint(env, arg, mty, explicit) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === $$Error$5) {
-      throw {
-            MEL_EXN_ID: $$Error$10,
-            _1: arg.mod_loc,
-            _2: env,
-            _3: {
-              TAG: /* Not_included */1,
-              _0: exn._1
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$10, {
+                cause: {
+                  MEL_EXN_ID: $$Error$10,
+                  _1: arg.mod_loc,
+                  _2: env,
+                  _3: {
+                    TAG: /* Not_included */1,
+                    _0: exn._1
+                  }
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
   return {
           mod_desc: {
@@ -84805,22 +86656,24 @@ function type_module$1(aliasOpt, sttn, funct_body, anchor, env, smod) {
                     TAG: /* Pmod_structure */1,
                     _0: /* [] */0
                   })) {
-              throw {
-                    MEL_EXN_ID: $$Error$10,
-                    _1: sfunct.pmod_loc,
-                    _2: env,
-                    _3: /* Apply_generative */4,
-                    Error: new Error()
-                  };
+              throw new Error($$Error$10, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$10,
+                          _1: sfunct.pmod_loc,
+                          _2: env,
+                          _3: /* Apply_generative */4
+                        }
+                      });
             }
             if (funct_body && contains_type$1(env, funct.mod_type)) {
-              throw {
-                    MEL_EXN_ID: $$Error$10,
-                    _1: smod.pmod_loc,
-                    _2: env,
-                    _3: /* Not_allowed_in_functor_body */1,
-                    Error: new Error()
-                  };
+              throw new Error($$Error$10, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$10,
+                          _1: smod.pmod_loc,
+                          _2: env,
+                          _3: /* Not_allowed_in_functor_body */1
+                        }
+                      });
             }
             
           }
@@ -84831,18 +86684,21 @@ function type_module$1(aliasOpt, sttn, funct_body, anchor, env, smod) {
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === $$Error$5) {
-              throw {
-                    MEL_EXN_ID: $$Error$10,
-                    _1: sarg.pmod_loc,
-                    _2: env,
-                    _3: {
-                      TAG: /* Not_included */1,
-                      _0: exn._1
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$10, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$10,
+                          _1: sarg.pmod_loc,
+                          _2: env,
+                          _3: {
+                            TAG: /* Not_included */1,
+                            _0: exn._1
+                          }
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           var mty_appl;
           if (path$1 !== undefined) {
@@ -84856,18 +86712,21 @@ function type_module$1(aliasOpt, sttn, funct_body, anchor, env, smod) {
             catch (raw_exn$1){
               var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
               if (exn$1.MEL_EXN_ID === Stdlib.Not_found) {
-                throw {
-                      MEL_EXN_ID: $$Error$10,
-                      _1: smod.pmod_loc,
-                      _2: env,
-                      _3: {
-                        TAG: /* Cannot_eliminate_dependency */2,
-                        _0: mty_functor
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$10, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$10,
+                            _1: smod.pmod_loc,
+                            _2: env,
+                            _3: {
+                              TAG: /* Cannot_eliminate_dependency */2,
+                              _0: mty_functor
+                            }
+                          }
+                        });
               }
-              throw exn$1;
+              throw new Error(exn$1.MEL_EXN_ID, {
+                        cause: exn$1
+                      });
             }
           }
           var node_mod_desc$2 = {
@@ -84891,16 +86750,17 @@ function type_module$1(aliasOpt, sttn, funct_body, anchor, env, smod) {
               });
           return node$3;
         }
-        throw {
-              MEL_EXN_ID: $$Error$10,
-              _1: sfunct.pmod_loc,
-              _2: env,
-              _3: {
-                TAG: /* Cannot_apply */0,
-                _0: funct.mod_type
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$10, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$10,
+                    _1: sfunct.pmod_loc,
+                    _2: env,
+                    _3: {
+                      TAG: /* Cannot_apply */0,
+                      _0: funct.mod_type
+                    }
+                  }
+                });
     case /* Pmod_constraint */4 :
         var arg$1 = type_module$1(alias, true, funct_body, anchor, env, lid._0);
         var mty$3 = transl_modtype$1(env, lid._1);
@@ -84942,28 +86802,30 @@ function type_module$1(aliasOpt, sttn, funct_body, anchor, env, smod) {
         } else {
           switch (match$4.TAG | 0) {
             case /* Tvar */0 :
-                throw {
-                      MEL_EXN_ID: $$Error$7,
-                      _1: smod.pmod_loc,
-                      _2: env,
-                      _3: /* Cannot_infer_signature */3,
-                      Error: new Error()
-                    };
+                throw new Error($$Error$7, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$7,
+                            _1: smod.pmod_loc,
+                            _2: env,
+                            _3: /* Cannot_infer_signature */3
+                          }
+                        });
             case /* Tpackage */11 :
                 var tl = match$4._2;
                 if (Stdlib__List.exists((function (t) {
                           return Caml_obj.caml_notequal(free_variables$1(undefined, t), /* [] */0);
                         }), tl)) {
-                  throw {
-                        MEL_EXN_ID: $$Error$10,
-                        _1: smod.pmod_loc,
-                        _2: env,
-                        _3: {
-                          TAG: /* Incomplete_packed_module */13,
-                          _0: exp.exp_type
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$10, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$10,
+                              _1: smod.pmod_loc,
+                              _2: env,
+                              _3: {
+                                TAG: /* Incomplete_packed_module */13,
+                                _0: exp.exp_type
+                              }
+                            }
+                          });
                 }
                 if (principal.contents && !generalizable(99999999, exp.exp_type)) {
                   prerr_warning(smod.pmod_loc, {
@@ -84978,25 +86840,27 @@ function type_module$1(aliasOpt, sttn, funct_body, anchor, env, smod) {
           }
         }
         if (exit$1 === 1) {
-          throw {
-                MEL_EXN_ID: $$Error$10,
-                _1: smod.pmod_loc,
-                _2: env,
-                _3: {
-                  TAG: /* Not_a_packed_module */12,
-                  _0: exp.exp_type
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$10, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$10,
+                      _1: smod.pmod_loc,
+                      _2: env,
+                      _3: {
+                        TAG: /* Not_a_packed_module */12,
+                        _0: exp.exp_type
+                      }
+                    }
+                  });
         }
         if (funct_body && contains_type$1(env, mty$4)) {
-          throw {
-                MEL_EXN_ID: $$Error$10,
-                _1: smod.pmod_loc,
-                _2: env,
-                _3: /* Not_allowed_in_functor_body */1,
-                Error: new Error()
-              };
+          throw new Error($$Error$10, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$10,
+                      _1: smod.pmod_loc,
+                      _2: env,
+                      _3: /* Not_allowed_in_functor_body */1
+                    }
+                  });
         }
         var node_mod_desc$4 = {
           TAG: /* Tmod_unpack */5,
@@ -85018,11 +86882,12 @@ function type_module$1(aliasOpt, sttn, funct_body, anchor, env, smod) {
             });
         return node$5;
     case /* Pmod_extension */6 :
-        throw {
-              MEL_EXN_ID: Error_forward$3,
-              _1: error_of_extension(lid._0),
-              Error: new Error()
-            };
+        throw new Error(Error_forward$3, {
+                  cause: {
+                    MEL_EXN_ID: Error_forward$3,
+                    _1: error_of_extension(lid._0)
+                  }
+                });
     
   }
 }
@@ -85228,13 +87093,14 @@ function type_structure(toplevelOpt, funct_body, anchor, env, sstr, scope) {
                             mb.pmb_loc
                           ];
                   }
-                  throw {
-                        MEL_EXN_ID: $$Error$10,
-                        _1: mb.pmb_expr.pmod_loc,
-                        _2: env,
-                        _3: /* Recursive_module_require_explicit_type */3,
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$10, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$10,
+                              _1: mb.pmb_expr.pmod_loc,
+                              _2: env,
+                              _3: /* Recursive_module_require_explicit_type */3
+                            }
+                          });
                 }), desc._0);
           Stdlib__List.iter((function (param) {
                   check_name("module", module_names, param[0]);
@@ -85519,11 +87385,12 @@ function type_structure(toplevelOpt, funct_body, anchor, env, sstr, scope) {
                   env
                 ];
       case /* Pstr_extension */14 :
-          throw {
-                MEL_EXN_ID: Error_forward$3,
-                _1: error_of_extension(desc._0),
-                Error: new Error()
-              };
+          throw new Error(Error_forward$3, {
+                    cause: {
+                      MEL_EXN_ID: Error_forward$3,
+                      _1: error_of_extension(desc._0)
+                    }
+                  });
       
     }
   };
@@ -85672,16 +87539,17 @@ function type_module_type_of(env, smod) {
   var mty = tmty.mod_type;
   var mty$1 = remove_aliases$1(env, mty);
   if (!closed_modtype(mty$1)) {
-    throw {
-          MEL_EXN_ID: $$Error$10,
-          _1: smod.pmod_loc,
-          _2: env,
-          _3: {
-            TAG: /* Non_generalizable_module */9,
-            _0: mty$1
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$10, {
+              cause: {
+                MEL_EXN_ID: $$Error$10,
+                _1: smod.pmod_loc,
+                _2: env,
+                _3: {
+                  TAG: /* Non_generalizable_module */9,
+                  _0: mty$1
+                }
+              }
+            });
   }
   return [
           tmty,
@@ -85733,15 +87601,16 @@ function type_package$1(env, m, p, nl, tl) {
                   _2: -1
                 };
       case /* Lapply */2 :
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "jscomp/test/ocaml_typedtree_test.ml",
-                  51527,
-                  11
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "jscomp/test/ocaml_typedtree_test.ml",
+                        51527,
+                        11
+                      ]
+                    }
+                  });
       
     }
   };
@@ -85773,19 +87642,22 @@ function type_package$1(env, m, p, nl, tl) {
           catch (raw_exn){
             var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
             if (exn.MEL_EXN_ID === Unify) {
-              throw {
-                    MEL_EXN_ID: $$Error$10,
-                    _1: m.pmod_loc,
-                    _2: env$1,
-                    _3: {
-                      TAG: /* Scoping_pack */14,
-                      _0: n,
-                      _1: ty
-                    },
-                    Error: new Error()
-                  };
+              throw new Error($$Error$10, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$10,
+                          _1: m.pmod_loc,
+                          _2: env$1,
+                          _3: {
+                            TAG: /* Scoping_pack */14,
+                            _0: n,
+                            _1: ty
+                          }
+                        }
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }), nl, tl$p);
   return [
@@ -85850,18 +87722,21 @@ function type_implementation_more(sourcefile, outputprefix, modulename, initial_
       catch (raw_exn){
         var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
         if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-          throw {
-                MEL_EXN_ID: $$Error$10,
-                _1: in_file(sourcefile),
-                _2: empty,
-                _3: {
-                  TAG: /* Interface_not_compiled */11,
-                  _0: sourceintf
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$10, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$10,
+                      _1: in_file(sourcefile),
+                      _2: empty,
+                      _3: {
+                        TAG: /* Interface_not_compiled */11,
+                        _0: sourceintf
+                      }
+                    }
+                  });
         }
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
       var dclsig = read_signature(modulename, intf_file);
       var coercion = compunit(initial_env, sourcefile, sg, intf_file, dclsig);
@@ -85886,32 +87761,34 @@ function type_implementation_more(sourcefile, outputprefix, modulename, initial_
                                 if (closed_schema(exp.exp_type)) {
                                   return ;
                                 }
-                                throw {
-                                      MEL_EXN_ID: $$Error$10,
-                                      _1: exp.exp_loc,
-                                      _2: finalenv,
-                                      _3: {
-                                        TAG: /* Non_generalizable */7,
-                                        _0: exp.exp_type
-                                      },
-                                      Error: new Error()
-                                    };
+                                throw new Error($$Error$10, {
+                                          cause: {
+                                            MEL_EXN_ID: $$Error$10,
+                                            _1: exp.exp_loc,
+                                            _2: finalenv,
+                                            _3: {
+                                              TAG: /* Non_generalizable */7,
+                                              _0: exp.exp_type
+                                            }
+                                          }
+                                        });
                               }), match._1);
               case /* Tstr_module */6 :
                   var md = match._0.mb_expr;
                   if (closed_modtype(md.mod_type)) {
                     return ;
                   }
-                  throw {
-                        MEL_EXN_ID: $$Error$10,
-                        _1: md.mod_loc,
-                        _2: finalenv,
-                        _3: {
-                          TAG: /* Non_generalizable_module */9,
-                          _0: md.mod_type
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$10, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$10,
+                              _1: md.mod_loc,
+                              _2: finalenv,
+                              _3: {
+                                TAG: /* Non_generalizable_module */9,
+                                _0: md.mod_type
+                              }
+                            }
+                          });
               default:
                 return ;
             }
@@ -85938,7 +87815,9 @@ function type_implementation_more(sourcefile, outputprefix, modulename, initial_
           TAG: /* Partial_implementation */3,
           _0: Stdlib__Array.of_list(saved_types.contents)
         }, sourcefile, initial_env, undefined);
-    throw e;
+    throw new Error(e.MEL_EXN_ID, {
+              cause: e
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/offset.js b/jscomp/test/dist/jscomp/test/offset.js
index 0cdfaffd4f..e337946a43 100644
--- a/jscomp/test/dist/jscomp/test/offset.js
+++ b/jscomp/test/dist/jscomp/test/offset.js
@@ -46,17 +46,19 @@ function bal(l, v, r) {
       if (lr) {
         return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -76,17 +78,19 @@ function bal(l, v, r) {
     if (rl) {
       return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add(x, t) {
@@ -175,10 +179,11 @@ function min_elt(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -207,10 +212,11 @@ function max_elt(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -237,11 +243,12 @@ function remove_min_elt(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.remove_min_elt"
+            }
+          });
 }
 
 function concat(t1, t2) {
@@ -723,10 +730,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -757,10 +765,11 @@ function find_first(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -822,10 +831,11 @@ function find_last(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1040,15 +1050,16 @@ function of_list(l) {
                   match$4[1]
                 ];
         }
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/stdlib/set.ml",
-                571,
-                18
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/stdlib/set.ml",
+                      571,
+                      18
+                    ]
+                  }
+                });
       };
       return sub(Stdlib__List.length(l$1), l$1)[0];
     } else {
diff --git a/jscomp/test/dist/jscomp/test/parser_api.js b/jscomp/test/dist/jscomp/test/parser_api.js
index b92e202987..73b10b7bbd 100644
--- a/jscomp/test/dist/jscomp/test/parser_api.js
+++ b/jscomp/test/dist/jscomp/test/parser_api.js
@@ -45,7 +45,9 @@ catch (raw_exn){
   if (exn.MEL_EXN_ID === Stdlib.Not_found) {
     standard_library = standard_library_default;
   } else {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -777,10 +779,11 @@ var Fatal_error = /* @__PURE__ */Caml_exceptions.create("Parser_api.Misc.Fatal_e
 function fatal_error(msg) {
   Stdlib.prerr_string(">> Fatal error: ");
   console.error(msg);
-  throw {
-        MEL_EXN_ID: Fatal_error,
-        Error: new Error()
-      };
+  throw new Error(Fatal_error, {
+            cause: {
+              MEL_EXN_ID: Fatal_error
+            }
+          });
 }
 
 function try_finally(work, cleanup) {
@@ -790,7 +793,9 @@ function try_finally(work, cleanup) {
   }
   catch (e){
     Curry._1(cleanup, undefined);
-    throw e;
+    throw new Error(e.MEL_EXN_ID, {
+              cause: e
+            });
   }
   Curry._1(cleanup, undefined);
   return result;
@@ -886,15 +891,16 @@ function split_last(param) {
             match[1]
           ];
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "misc.ml",
-          54,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "misc.ml",
+                54,
+                10
+              ]
+            }
+          });
 }
 
 function samelist(pred, _l1, _l2) {
@@ -947,19 +953,21 @@ function find_in_path(path, name) {
         _param = param.tl;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     };
   }
   if (Caml_external_polyfill.resolve("caml_sys_file_exists")(name)) {
     return name;
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function find_in_path_rel(path, name) {
@@ -989,10 +997,11 @@ function find_in_path_rel(path, name) {
       _param = param.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1014,10 +1023,11 @@ function find_in_path_uncap(path, name) {
       _param = param.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1030,7 +1040,9 @@ function remove_file(filename) {
     if (exn.MEL_EXN_ID === Stdlib.Sys_error) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -1074,10 +1086,11 @@ function copy_file_chunk(ic, oc, len) {
     }
     var r = Stdlib.input(ic, buff, 0, n < 4096 ? n : 4096);
     if (r === 0) {
-      throw {
-            MEL_EXN_ID: Stdlib.End_of_file,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.End_of_file, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.End_of_file
+                }
+              });
     }
     Stdlib.output(oc, buff, 0, r);
     _n = n - r | 0;
@@ -1141,7 +1154,9 @@ function chop_extension_if_any(fname) {
     if (exn.MEL_EXN_ID === Stdlib.Invalid_argument) {
       return fname;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -1162,7 +1177,9 @@ function chop_extensions(file) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return file;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -1176,10 +1193,11 @@ function search_substring(pat, str, start) {
       return i;
     }
     if ((i + j | 0) >= str.length) {
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     }
     if (Caml_string.get(str, i + j | 0) === Caml_string.get(pat, j)) {
       _j = j + 1 | 0;
@@ -1209,7 +1227,9 @@ function replace_substring(before, after, str) {
                       tl: acc
                     });
         }
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
       var prefix = Stdlib__String.sub(str, curr, next - curr | 0);
       _curr = next + before.length | 0;
@@ -1421,7 +1441,9 @@ function split(s, c) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         pos2 = undefined;
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
     if (pos2 === undefined) {
@@ -1576,21 +1598,23 @@ function style_of_tag(param) {
       case "warning" :
           return cur_styles.contents.warning;
       default:
-        throw {
-              MEL_EXN_ID: Stdlib.Not_found,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Not_found, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Not_found
+                  }
+                });
     }
   } else {
-    throw {
-          MEL_EXN_ID: "Match_failure",
-          _1: [
-            "misc.ml",
-            428,
-            19
-          ],
-          Error: new Error()
-        };
+    throw new Error("Match_failure", {
+              cause: {
+                MEL_EXN_ID: "Match_failure",
+                _1: [
+                  "misc.ml",
+                  428,
+                  19
+                ]
+              }
+            });
   }
 }
 
@@ -1616,7 +1640,9 @@ function set_color_tag_handling(ppf) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         return Curry._1(partial_arg, param);
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   var functions$p_mark_close_stag = function (param) {
@@ -1636,7 +1662,9 @@ function set_color_tag_handling(ppf) {
       if (exn.MEL_EXN_ID === Stdlib.Not_found) {
         return Curry._1(partial_arg$1, param);
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   var functions$p_print_open_stag = functions.print_open_stag;
@@ -2038,15 +2066,16 @@ function letter(param) {
                 tl: /* [] */0
               };
     default:
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "warnings.ml",
-              176,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "warnings.ml",
+                    176,
+                    9
+                  ]
+                }
+              });
   }
 }
 
@@ -2120,11 +2149,12 @@ function parse_opt(error, active, flags, s) {
     var match$1 = get_num(0, i$1 + 2 | 0);
     var n2 = match$1[1];
     if (n2 < n1) {
-      throw {
-            MEL_EXN_ID: Stdlib__Arg.Bad,
-            _1: "Ill-formed list of warnings",
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Arg.Bad, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Arg.Bad,
+                  _1: "Ill-formed list of warnings"
+                }
+              });
     }
     return [
             match$1[0],
@@ -2142,22 +2172,24 @@ function parse_opt(error, active, flags, s) {
       if (c >= 65) {
         if (c >= 97) {
           if (c >= 123) {
-            throw {
-                  MEL_EXN_ID: Stdlib__Arg.Bad,
-                  _1: "Ill-formed list of warnings",
-                  Error: new Error()
-                };
+            throw new Error(Stdlib__Arg.Bad, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib__Arg.Bad,
+                        _1: "Ill-formed list of warnings"
+                      }
+                    });
           }
           Stdlib__List.iter(clear, letter(Caml_string.get(s, i)));
           _i = i + 1 | 0;
           continue ;
         }
         if (c >= 91) {
-          throw {
-                MEL_EXN_ID: Stdlib__Arg.Bad,
-                _1: "Ill-formed list of warnings",
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Arg.Bad, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Arg.Bad,
+                      _1: "Ill-formed list of warnings"
+                    }
+                  });
         }
         Stdlib__List.iter(set, letter(Stdlib__Char.lowercase_ascii(Caml_string.get(s, i))));
         _i = i + 1 | 0;
@@ -2167,72 +2199,79 @@ function parse_opt(error, active, flags, s) {
         if (c >= 64) {
           return loop_letter_num(set_all, i + 1 | 0);
         }
-        throw {
-              MEL_EXN_ID: Stdlib__Arg.Bad,
-              _1: "Ill-formed list of warnings",
-              Error: new Error()
-            };
+        throw new Error(Stdlib__Arg.Bad, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib__Arg.Bad,
+                    _1: "Ill-formed list of warnings"
+                  }
+                });
       }
       if (c >= 43) {
         switch (c) {
           case 43 :
               return loop_letter_num(set, i + 1 | 0);
           case 44 :
-              throw {
-                    MEL_EXN_ID: Stdlib__Arg.Bad,
-                    _1: "Ill-formed list of warnings",
-                    Error: new Error()
-                  };
+              throw new Error(Stdlib__Arg.Bad, {
+                        cause: {
+                          MEL_EXN_ID: Stdlib__Arg.Bad,
+                          _1: "Ill-formed list of warnings"
+                        }
+                      });
           case 45 :
               return loop_letter_num(clear, i + 1 | 0);
           
         }
       } else {
-        throw {
-              MEL_EXN_ID: Stdlib__Arg.Bad,
-              _1: "Ill-formed list of warnings",
-              Error: new Error()
-            };
+        throw new Error(Stdlib__Arg.Bad, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib__Arg.Bad,
+                    _1: "Ill-formed list of warnings"
+                  }
+                });
       }
     };
   };
   var loop_letter_num = function (myset, i) {
     if (i >= s.length) {
-      throw {
-            MEL_EXN_ID: Stdlib__Arg.Bad,
-            _1: "Ill-formed list of warnings",
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Arg.Bad, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Arg.Bad,
+                  _1: "Ill-formed list of warnings"
+                }
+              });
     }
     var match = Caml_string.get(s, i);
     if (match >= 65) {
       if (match >= 97) {
         if (match >= 123) {
-          throw {
-                MEL_EXN_ID: Stdlib__Arg.Bad,
-                _1: "Ill-formed list of warnings",
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Arg.Bad, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Arg.Bad,
+                      _1: "Ill-formed list of warnings"
+                    }
+                  });
         }
         Stdlib__List.iter(myset, letter(Caml_string.get(s, i)));
         return loop(i + 1 | 0);
       }
       if (match >= 91) {
-        throw {
-              MEL_EXN_ID: Stdlib__Arg.Bad,
-              _1: "Ill-formed list of warnings",
-              Error: new Error()
-            };
+        throw new Error(Stdlib__Arg.Bad, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib__Arg.Bad,
+                    _1: "Ill-formed list of warnings"
+                  }
+                });
       }
       Stdlib__List.iter(myset, letter(Stdlib__Char.lowercase_ascii(Caml_string.get(s, i))));
       return loop(i + 1 | 0);
     }
     if (match > 57 || match < 48) {
-      throw {
-            MEL_EXN_ID: Stdlib__Arg.Bad,
-            _1: "Ill-formed list of warnings",
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Arg.Bad, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Arg.Bad,
+                  _1: "Ill-formed list of warnings"
+                }
+              });
     }
     var match$1 = get_range(i);
     for(var n = match$1[1] ,n_finish = Caml.caml_int_min(match$1[2], 104); n <= n_finish; ++n){
@@ -2330,15 +2369,16 @@ function message(param) {
               return "the method " + (lab + " is overridden.");
             }
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "warnings.ml",
-                  283,
-                  26
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "warnings.ml",
+                        283,
+                        26
+                      ]
+                    }
+                  });
       case /* Partial_match */3 :
           var s$1 = param._0;
           if (s$1 === "") {
@@ -2367,15 +2407,16 @@ function message(param) {
               return "the instance variable " + (lab$1 + " is overridden.\nThe behaviour changed in ocaml 3.10 (previous behaviour was hiding.)");
             }
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "warnings.ml",
-                  303,
-                  37
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "warnings.ml",
+                        303,
+                        37
+                      ]
+                    }
+                  });
       case /* Implicit_public_methods */6 :
           return "the following private methods were made public implicitly:\n " + (Stdlib__String.concat(" ", param._0) + ".");
       case /* Undeclared_virtual_method */7 :
@@ -2498,15 +2539,16 @@ function message(param) {
           if (param._2) {
             return "this record of type " + (ty + (" contains fields that are \nnot visible in the current scope: " + (Stdlib__String.concat(" ", slist) + ".\nThey will not be selected if the type becomes unknown.")));
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "warnings.ml",
-                  365,
-                  39
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "warnings.ml",
+                        365,
+                        39
+                      ]
+                    }
+                  });
           break;
       case /* Ambiguous_name */24 :
           var slist$1 = param._0;
@@ -2516,15 +2558,16 @@ function message(param) {
           if (param._2) {
             return "these field labels belong to several types: " + (Stdlib__String.concat(" ", param._1) + "\nThe first one was selected. Please disambiguate if this is wrong.");
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "warnings.ml",
-                  374,
-                  36
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "warnings.ml",
+                        374,
+                        36
+                      ]
+                    }
+                  });
           break;
       case /* Disambiguated_name */25 :
           return "this use of " + (param._0 + " required disambiguation.");
@@ -2727,7 +2770,9 @@ function check_fatal(param) {
     _1: e_1
   };
   nerrors.contents = 0;
-  throw e;
+  throw new Error(e.MEL_EXN_ID, {
+            cause: e
+          });
 }
 
 function help_warnings(param) {
@@ -3261,10 +3306,11 @@ function highlight_terminfo(ppf, num_lines, lb, locs) {
   Stdlib__Format.pp_print_flush(ppf, undefined);
   var pos0 = -lb.lex_abs_pos | 0;
   if (pos0 < 0) {
-    throw {
-          MEL_EXN_ID: Stdlib.Exit,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Exit, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Exit
+              }
+            });
   }
   var lines = num_loc_lines.contents;
   for(var i = pos0 ,i_finish = lb.lex_buffer_len; i < i_finish; ++i){
@@ -3274,10 +3320,11 @@ function highlight_terminfo(ppf, num_lines, lb, locs) {
     
   }
   if (lines >= (num_lines - 2 | 0)) {
-    throw {
-          MEL_EXN_ID: Stdlib.Exit,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Exit, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Exit
+              }
+            });
   }
   Caml_io.caml_ml_flush(Stdlib.stdout);
   Caml_external_polyfill.resolve("caml_terminfo_backup")(lines);
@@ -3314,10 +3361,11 @@ function highlight_terminfo(ppf, num_lines, lb, locs) {
 function highlight_dumb(ppf, lb, loc) {
   var pos0 = -lb.lex_abs_pos | 0;
   if (pos0 < 0) {
-    throw {
-          MEL_EXN_ID: Stdlib.Exit,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Exit, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Exit
+              }
+            });
   }
   var end_pos = (lb.lex_buffer_len - pos0 | 0) - 1 | 0;
   var line_start = 0;
@@ -3452,7 +3500,9 @@ function highlight_locations(ppf, locs) {
           if (exn.MEL_EXN_ID === Stdlib.Not_found) {
             norepeat = false;
           } else {
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
         }
         if (norepeat) {
@@ -3468,7 +3518,9 @@ function highlight_locations(ppf, locs) {
           if (exn$1.MEL_EXN_ID === Stdlib.Exit) {
             return false;
           }
-          throw exn$1;
+          throw new Error(exn$1.MEL_EXN_ID, {
+                    cause: exn$1
+                  });
         }
       } else {
         status.contents = Caml_external_polyfill.resolve("caml_terminfo_setup")(Stdlib.stdout);
@@ -3488,7 +3540,9 @@ function highlight_locations(ppf, locs) {
         if (exn$2.MEL_EXN_ID === Stdlib.Exit) {
           return false;
         }
-        throw exn$2;
+        throw new Error(exn$2.MEL_EXN_ID, {
+                  cause: exn$2
+                });
       }
     }
   };
@@ -4067,7 +4121,9 @@ function report_exception(ppf, exn) {
                         _1: "@[%a@]@."
                       }), report_error, err);
       }
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
     catch (raw_exn){
       var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn);
@@ -4076,7 +4132,9 @@ function report_exception(ppf, exn) {
         _n = n - 1 | 0;
         continue ;
       }
-      throw exn$2;
+      throw new Error(exn$2.MEL_EXN_ID, {
+                cause: exn$2
+              });
     }
   };
 }
@@ -4097,16 +4155,17 @@ function raise_errorf(locOpt, subOpt, if_highlightOpt) {
   var partial_arg = print_phanton_error_prefix;
   return function (param) {
     return pp_ksprintf(partial_arg, (function (msg) {
-                  throw {
-                        MEL_EXN_ID: $$Error,
-                        _1: {
-                          loc: loc,
-                          msg: msg,
-                          sub: sub,
-                          if_highlight: if_highlight
-                        },
-                        Error: new Error()
-                      };
+                  throw new Error($$Error, {
+                            cause: {
+                              MEL_EXN_ID: $$Error,
+                              _1: {
+                                loc: loc,
+                                msg: msg,
+                                sub: sub,
+                                if_highlight: if_highlight
+                              }
+                            }
+                          });
                 }), param);
   };
 }
@@ -4212,7 +4271,9 @@ function split_at_dots(s, pos) {
               tl: /* [] */0
             };
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4498,7 +4559,9 @@ function get_pre_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4511,7 +4574,9 @@ function mark_pre_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4535,7 +4600,9 @@ function get_post_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4548,7 +4615,9 @@ function mark_post_docs(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4562,7 +4631,9 @@ function get_info(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4584,7 +4655,9 @@ function get_text(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4606,7 +4679,9 @@ function get_pre_extra_text(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4628,7 +4703,9 @@ function get_post_extra_text(pos) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return /* [] */0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4797,7 +4874,9 @@ function with_default_loc(l, f) {
   }
   catch (exn){
     default_loc.contents = old;
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -6752,15 +6831,16 @@ function location_of_error(param) {
 }
 
 function ill_formed_ast(loc, s) {
-  throw {
-        MEL_EXN_ID: $$Error$1,
-        _1: {
-          TAG: /* Ill_formed_ast */6,
-          _0: loc,
-          _1: s
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$1, {
+            cause: {
+              MEL_EXN_ID: $$Error$1,
+              _1: {
+                TAG: /* Ill_formed_ast */6,
+                _0: loc,
+                _1: s
+              }
+            }
+          });
 }
 
 var Syntaxerr = {
@@ -7088,15 +7168,16 @@ function mkexp_constraint(e, param) {
                 _2: t2
               });
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "parsing/parser.mly",
-          153,
-          18
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "parsing/parser.mly",
+                153,
+                18
+              ]
+            }
+          });
 }
 
 function array_function(str, name) {
@@ -7114,41 +7195,44 @@ function array_function(str, name) {
 }
 
 function unclosed(opening_name, opening_num, closing_name, closing_num) {
-  throw {
-        MEL_EXN_ID: $$Error$1,
-        _1: {
-          TAG: /* Unclosed */0,
-          _0: rhs_loc(opening_num),
-          _1: opening_name,
-          _2: rhs_loc(closing_num),
-          _3: closing_name
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$1, {
+            cause: {
+              MEL_EXN_ID: $$Error$1,
+              _1: {
+                TAG: /* Unclosed */0,
+                _0: rhs_loc(opening_num),
+                _1: opening_name,
+                _2: rhs_loc(closing_num),
+                _3: closing_name
+              }
+            }
+          });
 }
 
 function expecting(pos, nonterm) {
-  throw {
-        MEL_EXN_ID: $$Error$1,
-        _1: {
-          TAG: /* Expecting */1,
-          _0: rhs_loc(pos),
-          _1: nonterm
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$1, {
+            cause: {
+              MEL_EXN_ID: $$Error$1,
+              _1: {
+                TAG: /* Expecting */1,
+                _0: rhs_loc(pos),
+                _1: nonterm
+              }
+            }
+          });
 }
 
 function not_expecting(pos, nonterm) {
-  throw {
-        MEL_EXN_ID: $$Error$1,
-        _1: {
-          TAG: /* Not_expecting */2,
-          _0: rhs_loc(pos),
-          _1: nonterm
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$1, {
+            cause: {
+              MEL_EXN_ID: $$Error$1,
+              _1: {
+                TAG: /* Not_expecting */2,
+                _0: rhs_loc(pos),
+                _1: nonterm
+              }
+            }
+          });
 }
 
 function bigarray_function(str, name) {
@@ -7210,15 +7294,16 @@ function check_variable(vl, loc, v) {
   if (!Stdlib__List.mem(v, vl)) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: $$Error$1,
-        _1: {
-          TAG: /* Variable_in_scope */4,
-          _0: loc,
-          _1: v
-        },
-        Error: new Error()
-      };
+  throw new Error($$Error$1, {
+            cause: {
+              MEL_EXN_ID: $$Error$1,
+              _1: {
+                TAG: /* Variable_in_scope */4,
+                _0: loc,
+                _1: v
+              }
+            }
+          });
 }
 
 function varify_constructors(var_names, t) {
@@ -7626,11 +7711,12 @@ var yytransl_block = [
 
 var yyact = [
   (function (param) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "parser",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "parser"
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -7651,10 +7737,11 @@ var yyact = [
       return Stdlib__Parsing.peek_val(__caml_parser_env, 1);
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib.End_of_file,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.End_of_file, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.End_of_file
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
@@ -8041,15 +8128,16 @@ var yyact = [
       }
       if (exit === 1) {
         if (Caml_obj.caml_notequal(lbs.lbs_attributes, /* [] */0)) {
-          throw {
-                MEL_EXN_ID: $$Error$1,
-                _1: {
-                  TAG: /* Not_expecting */2,
-                  _0: lbs.lbs_loc,
-                  _1: "attributes"
-                },
-                Error: new Error()
-              };
+          throw new Error($$Error$1, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$1,
+                      _1: {
+                        TAG: /* Not_expecting */2,
+                        _0: lbs.lbs_loc,
+                        _1: "attributes"
+                      }
+                    }
+                  });
         }
         var bindings$1 = Stdlib__List.map((function (lb) {
                 return mk$17(lb.lb_loc, lb.lb_attributes, CamlinternalLazy.force(lb.lb_docs), CamlinternalLazy.force(lb.lb_text), lb.lb_pattern, lb.lb_expression);
@@ -8655,39 +8743,42 @@ var yyact = [
       var _3 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       var bindings = Stdlib__List.map((function (lb) {
               if (Caml_obj.caml_notequal(lb.lb_attributes, /* [] */0)) {
-                throw {
-                      MEL_EXN_ID: $$Error$1,
-                      _1: {
-                        TAG: /* Not_expecting */2,
-                        _0: lb.lb_loc,
-                        _1: "item attribute"
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$1, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$1,
+                            _1: {
+                              TAG: /* Not_expecting */2,
+                              _0: lb.lb_loc,
+                              _1: "item attribute"
+                            }
+                          }
+                        });
               }
               return mk$17(lb.lb_loc, undefined, undefined, undefined, lb.lb_pattern, lb.lb_expression);
             }), _1.lbs_bindings);
       if (_1.lbs_extension !== undefined) {
-        throw {
-              MEL_EXN_ID: $$Error$1,
-              _1: {
-                TAG: /* Not_expecting */2,
-                _0: _1.lbs_loc,
-                _1: "extension"
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$1, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$1,
+                    _1: {
+                      TAG: /* Not_expecting */2,
+                      _0: _1.lbs_loc,
+                      _1: "extension"
+                    }
+                  }
+                });
       }
       if (Caml_obj.caml_notequal(_1.lbs_attributes, /* [] */0)) {
-        throw {
-              MEL_EXN_ID: $$Error$1,
-              _1: {
-                TAG: /* Not_expecting */2,
-                _0: _1.lbs_loc,
-                _1: "attributes"
-              },
-              Error: new Error()
-            };
+        throw new Error($$Error$1, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$1,
+                    _1: {
+                      TAG: /* Not_expecting */2,
+                      _0: _1.lbs_loc,
+                      _1: "attributes"
+                    }
+                  }
+                });
       }
       return mkclass({
                   TAG: /* Pcl_let */4,
@@ -8868,10 +8959,11 @@ var yyact = [
       var _4 = Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       var _6 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       if (_1 === /* Override */0) {
-        throw {
-              MEL_EXN_ID: Escape_error,
-              Error: new Error()
-            };
+        throw new Error(Escape_error, {
+                  cause: {
+                    MEL_EXN_ID: Escape_error
+                  }
+                });
       }
       return [
               {
@@ -8944,10 +9036,11 @@ var yyact = [
       var _4 = Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       var _6 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       if (_1 === /* Override */0) {
-        throw {
-              MEL_EXN_ID: Escape_error,
-              Error: new Error()
-            };
+        throw new Error(Escape_error, {
+                  cause: {
+                    MEL_EXN_ID: Escape_error
+                  }
+                });
       }
       return [
               {
@@ -8967,10 +9060,11 @@ var yyact = [
       var _4 = Stdlib__Parsing.peek_val(__caml_parser_env, 2);
       var _6 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       if (_1 === /* Override */0) {
-        throw {
-              MEL_EXN_ID: Escape_error,
-              Error: new Error()
-            };
+        throw new Error(Escape_error, {
+                  cause: {
+                    MEL_EXN_ID: Escape_error
+                  }
+                });
       }
       return [
               {
@@ -9509,15 +9603,16 @@ var yyact = [
       var _3 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
       var bindings = Stdlib__List.map((function (lb) {
               if (Caml_obj.caml_notequal(lb.lb_attributes, /* [] */0)) {
-                throw {
-                      MEL_EXN_ID: $$Error$1,
-                      _1: {
-                        TAG: /* Not_expecting */2,
-                        _0: lb.lb_loc,
-                        _1: "item attribute"
-                      },
-                      Error: new Error()
-                    };
+                throw new Error($$Error$1, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$1,
+                            _1: {
+                              TAG: /* Not_expecting */2,
+                              _0: lb.lb_loc,
+                              _1: "item attribute"
+                            }
+                          }
+                        });
               }
               return mk$17(lb.lb_loc, undefined, undefined, undefined, lb.lb_pattern, lb.lb_expression);
             }), _1.lbs_bindings);
@@ -9629,10 +9724,11 @@ var yyact = [
   (function (__caml_parser_env) {
       Stdlib__Parsing.peek_val(__caml_parser_env, 3);
       Stdlib__Parsing.peek_val(__caml_parser_env, 2);
-      throw {
-            MEL_EXN_ID: Escape_error,
-            Error: new Error()
-          };
+      throw new Error(Escape_error, {
+                cause: {
+                  MEL_EXN_ID: Escape_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -11195,16 +11291,18 @@ var yyact = [
             ];
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Escape_error,
-            Error: new Error()
-          };
+      throw new Error(Escape_error, {
+                cause: {
+                  MEL_EXN_ID: Escape_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Escape_error,
-            Error: new Error()
-          };
+      throw new Error(Escape_error, {
+                cause: {
+                  MEL_EXN_ID: Escape_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -12340,17 +12438,19 @@ var yyact = [
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       if (_2) {
         if (_2.tl) {
-          throw {
-                MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Parsing.Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                    }
+                  });
         }
         return _2.hd;
       }
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.Parse_error, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       return Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -12359,17 +12459,19 @@ var yyact = [
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 1);
       if (_2) {
         if (_2.tl) {
-          throw {
-                MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-                Error: new Error()
-              };
+          throw new Error(Stdlib__Parsing.Parse_error, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                    }
+                  });
         }
         return _2.hd;
       }
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.Parse_error,
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.Parse_error, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.Parse_error
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _2 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -13151,14 +13253,15 @@ var yyact = [
                 _1: _3
               };
       }
-      throw {
-            MEL_EXN_ID: $$Error$1,
-            _1: {
-              TAG: /* Applicative_path */3,
-              _0: symbol_rloc(undefined)
-            },
-            Error: new Error()
-          };
+      throw new Error($$Error$1, {
+                cause: {
+                  MEL_EXN_ID: $$Error$1,
+                  _1: {
+                    TAG: /* Applicative_path */3,
+                    _0: symbol_rloc(undefined)
+                  }
+                }
+              });
     }),
   (function (__caml_parser_env) {
       var _1 = Stdlib__Parsing.peek_val(__caml_parser_env, 0);
@@ -13669,53 +13772,60 @@ var yyact = [
             };
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     }),
   (function (__caml_parser_env) {
-      throw {
-            MEL_EXN_ID: Stdlib__Parsing.YYexit,
-            _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0),
-            Error: new Error()
-          };
+      throw new Error(Stdlib__Parsing.YYexit, {
+                cause: {
+                  MEL_EXN_ID: Stdlib__Parsing.YYexit,
+                  _1: Stdlib__Parsing.peek_val(__caml_parser_env, 0)
+                }
+              });
     })
 ];
 
@@ -13815,16 +13925,17 @@ function assert_same_type(lexbuf, x, y) {
   var lhs = type_of_directive(x);
   var rhs = type_of_directive(y);
   if (lhs !== rhs) {
-    throw {
-          MEL_EXN_ID: $$Error$2,
-          _1: {
-            TAG: /* Conditional_expr_expected_type */7,
-            _0: lhs,
-            _1: rhs
-          },
-          _2: curr(lexbuf),
-          Error: new Error()
-        };
+    throw new Error($$Error$2, {
+              cause: {
+                MEL_EXN_ID: $$Error$2,
+                _1: {
+                  TAG: /* Conditional_expr_expected_type */7,
+                  _0: lhs,
+                  _1: rhs
+                },
+                _2: curr(lexbuf)
+              }
+            });
   }
   return y;
 }
@@ -13876,7 +13987,9 @@ catch (raw_exn$1){
   if (exn$2.MEL_EXN_ID === Stdlib.Not_found) {
     tmp = "";
   } else {
-    throw exn$2;
+    throw new Error(exn$2.MEL_EXN_ID, {
+              cause: exn$2
+            });
   }
 }
 
@@ -13952,15 +14065,16 @@ function semantic_version_parse(str, start, last_index) {
 function semver(loc, lhs, str) {
   var last_index = str.length - 1 | 0;
   if (last_index < 0) {
-    throw {
-          MEL_EXN_ID: $$Error$2,
-          _1: {
-            TAG: /* Illegal_semver */6,
-            _0: str
-          },
-          _2: loc,
-          Error: new Error()
-        };
+    throw new Error($$Error$2, {
+              cause: {
+                MEL_EXN_ID: $$Error$2,
+                _1: {
+                  TAG: /* Illegal_semver */6,
+                  _0: str
+                },
+                _2: loc
+              }
+            });
   }
   var v = str.charCodeAt(0);
   var match;
@@ -13979,15 +14093,16 @@ function semver(loc, lhs, str) {
       switch (v) {
         case 60 :
             if (last_index === 0) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Illegal_semver */6,
-                      _0: str
-                    },
-                    _2: loc,
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Illegal_semver */6,
+                            _0: str
+                          },
+                          _2: loc
+                        }
+                      });
             }
             match = str[1] === "=" ? [
                 "Le",
@@ -14002,15 +14117,16 @@ function semver(loc, lhs, str) {
             break;
         case 62 :
             if (last_index === 0) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Illegal_semver */6,
-                      _0: str
-                    },
-                    _2: loc,
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Illegal_semver */6,
+                            _0: str
+                          },
+                          _2: loc
+                        }
+                      });
             }
             match = str[1] === "=" ? [
                 "Ge",
@@ -14177,7 +14293,9 @@ function query(loc, str) {
                   _0: false
                 };
         }
-        throw exn$1;
+        throw new Error(exn$1.MEL_EXN_ID, {
+                  cause: exn$1
+                });
       }
       if (exit === 2) {
         try {
@@ -14211,7 +14329,9 @@ function query(loc, str) {
       }
       
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   if (typeof v === "number") {
@@ -14275,12 +14395,13 @@ function value_of_token(loc, t) {
                   _0: true
                 };
       default:
-        throw {
-              MEL_EXN_ID: $$Error$2,
-              _1: /* Unexpected_token_in_conditional */4,
-              _2: loc,
-              Error: new Error()
-            };
+        throw new Error($$Error$2, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$2,
+                    _1: /* Unexpected_token_in_conditional */4,
+                    _2: loc
+                  }
+                });
     }
   } else {
     switch (t.TAG | 0) {
@@ -14302,12 +14423,13 @@ function value_of_token(loc, t) {
       case /* UIDENT */17 :
           return query(loc, t._0);
       default:
-        throw {
-              MEL_EXN_ID: $$Error$2,
-              _1: /* Unexpected_token_in_conditional */4,
-              _2: loc,
-              Error: new Error()
-            };
+        throw new Error($$Error$2, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$2,
+                    _1: /* Unexpected_token_in_conditional */4,
+                    _2: loc
+                  }
+                });
     }
   }
 }
@@ -14328,12 +14450,13 @@ function directive_parse(token_with_comments, lexbuf) {
       if (typeof t === "number") {
         switch (t) {
           case /* EOF */25 :
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: /* Unterminated_if */2,
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: /* Unterminated_if */2,
+                          _2: curr(lexbuf)
+                        }
+                      });
           case /* EOL */100 :
               _param = undefined;
               continue ;
@@ -14354,15 +14477,16 @@ function directive_parse(token_with_comments, lexbuf) {
   };
   var push = function (e) {
     if (look_ahead.contents !== undefined) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "parsing/lexer.mll",
-              312,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "parsing/lexer.mll",
+                    312,
+                    4
+                  ]
+                }
+              });
     }
     look_ahead.contents = e;
   };
@@ -14404,30 +14528,32 @@ function directive_parse(token_with_comments, lexbuf) {
                 exit$2 = 3;
               }
               if (exit$2 === 3) {
-                throw {
-                      MEL_EXN_ID: $$Error$2,
-                      _1: {
-                        TAG: /* Conditional_expr_expected_type */7,
-                        _0: /* Dir_type_string */3,
-                        _1: type_of_directive(lhs)
-                      },
-                      _2: curr(lexbuf),
-                      Error: new Error()
-                    };
+                throw new Error($$Error$2, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$2,
+                            _1: {
+                              TAG: /* Conditional_expr_expected_type */7,
+                              _0: /* Dir_type_string */3,
+                              _1: type_of_directive(lhs)
+                            },
+                            _2: curr(lexbuf)
+                          }
+                        });
               }
               
             }
             if (exit$1 === 2) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Conditional_expr_expected_type */7,
-                      _0: /* Dir_type_string */3,
-                      _1: type_of_directive(lhs)
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Conditional_expr_expected_type */7,
+                            _0: /* Dir_type_string */3,
+                            _1: type_of_directive(lhs)
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
             break;
         case "<=" :
@@ -14471,15 +14597,16 @@ function directive_parse(token_with_comments, lexbuf) {
         exit$3 = 2;
       }
       if (exit$3 === 2) {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "parsing/lexer.mll",
-                331,
-                17
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "parsing/lexer.mll",
+                      331,
+                      17
+                    ]
+                  }
+                });
       }
       var curr_loc$1 = curr(lexbuf);
       var rhs$1 = value_of_token(curr_loc$1, token(undefined));
@@ -14536,36 +14663,39 @@ function directive_parse(token_with_comments, lexbuf) {
             if (match === 81) {
               return v;
             }
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: /* Unterminated_paren_in_conditional */1,
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: /* Unterminated_paren_in_conditional */1,
+                        _2: curr(lexbuf)
+                      }
+                    });
         case /* TRUE */91 :
             return true;
         default:
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unexpected_token_in_conditional */4,
-                _2: curr_loc,
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unexpected_token_in_conditional */4,
+                      _2: curr_loc
+                    }
+                  });
       }
     } else {
       switch (curr_token.TAG | 0) {
         case /* FLOAT */1 :
             return token_op(calc, (function (e) {
-                          throw {
-                                MEL_EXN_ID: $$Error$2,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: /* Dir_type_float */1
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$2, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$2,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: /* Dir_type_float */1
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), {
                         TAG: /* Dir_float */1,
                         _0: Caml_format.caml_float_of_string(curr_token._0)
@@ -14586,22 +14716,24 @@ function directive_parse(token_with_comments, lexbuf) {
               case "undefined" :
                   break;
               default:
-                throw {
-                      MEL_EXN_ID: $$Error$2,
-                      _1: /* Unexpected_token_in_conditional */4,
-                      _2: curr_loc,
-                      Error: new Error()
-                    };
+                throw new Error($$Error$2, {
+                          cause: {
+                            MEL_EXN_ID: $$Error$2,
+                            _1: /* Unexpected_token_in_conditional */4,
+                            _2: curr_loc
+                          }
+                        });
             }
             var t = token(undefined);
             var loc = curr(lexbuf);
             if (typeof t === "number") {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: /* Unexpected_token_in_conditional */4,
-                    _2: loc,
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: /* Unexpected_token_in_conditional */4,
+                          _2: loc
+                        }
+                      });
             }
             if (t.TAG === /* UIDENT */17) {
               var s = t._0;
@@ -14615,25 +14747,27 @@ function directive_parse(token_with_comments, lexbuf) {
                 return true;
               }
             }
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: /* Unexpected_token_in_conditional */4,
-                  _2: loc,
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: /* Unexpected_token_in_conditional */4,
+                        _2: loc
+                      }
+                    });
             break;
         case /* STRING */16 :
             return token_op(calc, (function (e) {
-                          throw {
-                                MEL_EXN_ID: $$Error$2,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: /* Dir_type_string */3
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$2, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$2,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: /* Dir_type_string */3
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), {
                         TAG: /* Dir_string */3,
                         _0: curr_token._0[0]
@@ -14646,24 +14780,26 @@ function directive_parse(token_with_comments, lexbuf) {
                             return value_v._0;
                           }
                           var ty = type_of_directive(value_v);
-                          throw {
-                                MEL_EXN_ID: $$Error$2,
-                                _1: {
-                                  TAG: /* Conditional_expr_expected_type */7,
-                                  _0: /* Dir_type_bool */0,
-                                  _1: ty
-                                },
-                                _2: curr_loc,
-                                Error: new Error()
-                              };
+                          throw new Error($$Error$2, {
+                                    cause: {
+                                      MEL_EXN_ID: $$Error$2,
+                                      _1: {
+                                        TAG: /* Conditional_expr_expected_type */7,
+                                        _0: /* Dir_type_bool */0,
+                                        _1: ty
+                                      },
+                                      _2: curr_loc
+                                    }
+                                  });
                         }), value_v);
         default:
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unexpected_token_in_conditional */4,
-                _2: curr_loc,
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unexpected_token_in_conditional */4,
+                      _2: curr_loc
+                    }
+                  });
       }
     }
   };
@@ -14672,12 +14808,13 @@ function directive_parse(token_with_comments, lexbuf) {
   if (match === 88) {
     return v;
   }
-  throw {
-        MEL_EXN_ID: $$Error$2,
-        _1: /* Expect_hash_then_in_conditional */5,
-        _2: curr(lexbuf),
-        Error: new Error()
-      };
+  throw new Error($$Error$2, {
+            cause: {
+              MEL_EXN_ID: $$Error$2,
+              _1: /* Expect_hash_then_in_conditional */5,
+              _2: curr(lexbuf)
+            }
+          });
 }
 
 function is_elif(i) {
@@ -15175,15 +15312,16 @@ function char_for_decimal_code(lexbuf, i) {
   if (Caml_obj.caml_notequal(comment_start_loc.contents, /* [] */0)) {
     return /* 'x' */120;
   }
-  throw {
-        MEL_EXN_ID: $$Error$2,
-        _1: {
-          TAG: /* Illegal_escape */1,
-          _0: Stdlib__Lexing.lexeme(lexbuf)
-        },
-        _2: curr(lexbuf),
-        Error: new Error()
-      };
+  throw new Error($$Error$2, {
+            cause: {
+              MEL_EXN_ID: $$Error$2,
+              _1: {
+                TAG: /* Illegal_escape */1,
+                _0: Stdlib__Lexing.lexeme(lexbuf)
+              },
+              _2: curr(lexbuf)
+            }
+          });
 }
 
 function char_for_hexadecimal_code(lexbuf, i) {
@@ -15211,15 +15349,16 @@ function cvt_int64_literal(s) {
 }
 
 function cvt_nativeint_literal(s) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "parsing/lexer.mll",
-          622,
-          30
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "parsing/lexer.mll",
+                622,
+                30
+              ]
+            }
+          });
 }
 
 function remove_underscores(s) {
@@ -15253,15 +15392,16 @@ function get_label_name(lexbuf) {
   var s = Stdlib__Lexing.lexeme(lexbuf);
   var name = Stdlib__String.sub(s, 1, s.length - 2 | 0);
   if (Stdlib__Hashtbl.mem(keyword_table, name)) {
-    throw {
-          MEL_EXN_ID: $$Error$2,
-          _1: {
-            TAG: /* Keyword_as_label */4,
-            _0: name
-          },
-          _2: curr(lexbuf),
-          Error: new Error()
-        };
+    throw new Error($$Error$2, {
+              cause: {
+                MEL_EXN_ID: $$Error$2,
+                _1: {
+                  TAG: /* Keyword_as_label */4,
+                  _0: name
+                },
+                _2: curr(lexbuf)
+              }
+            });
   }
   return name;
 }
@@ -15543,15 +15683,16 @@ function token(lexbuf) {
     switch (__ocaml_lex_state$1) {
       case 0 :
           if (!escaped_newlines.contents) {
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: {
-                    TAG: /* Illegal_character */0,
-                    _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
-                  },
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: {
+                          TAG: /* Illegal_character */0,
+                          _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
+                        },
+                        _2: curr(lexbuf)
+                      }
+                    });
           }
           update_loc(lexbuf, undefined, 1, false, 0);
           return token(lexbuf);
@@ -15607,7 +15748,9 @@ function token(lexbuf) {
                       _0: s
                     };
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
       case 11 :
           prerr_warning(curr(lexbuf), {
@@ -15642,17 +15785,20 @@ function token(lexbuf) {
           catch (raw_exn$1){
             var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
             if (exn$1.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "int"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "int"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
       case 15 :
           return {
@@ -15669,17 +15815,20 @@ function token(lexbuf) {
           catch (raw_exn$2){
             var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
             if (exn$2.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "int32"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "int32"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$2;
+            throw new Error(exn$2.MEL_EXN_ID, {
+                      cause: exn$2
+                    });
           }
       case 17 :
           try {
@@ -15691,17 +15840,20 @@ function token(lexbuf) {
           catch (raw_exn$3){
             var exn$3 = Caml_js_exceptions.internalToOCamlException(raw_exn$3);
             if (exn$3.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "int64"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "int64"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$3;
+            throw new Error(exn$3.MEL_EXN_ID, {
+                      cause: exn$3
+                    });
           }
       case 18 :
           try {
@@ -15713,17 +15865,20 @@ function token(lexbuf) {
           catch (raw_exn$4){
             var exn$4 = Caml_js_exceptions.internalToOCamlException(raw_exn$4);
             if (exn$4.MEL_EXN_ID === Stdlib.Failure) {
-              throw {
-                    MEL_EXN_ID: $$Error$2,
-                    _1: {
-                      TAG: /* Literal_overflow */5,
-                      _0: "nativeint"
-                    },
-                    _2: curr(lexbuf),
-                    Error: new Error()
-                  };
+              throw new Error($$Error$2, {
+                        cause: {
+                          MEL_EXN_ID: $$Error$2,
+                          _1: {
+                            TAG: /* Literal_overflow */5,
+                            _0: "nativeint"
+                          },
+                          _2: curr(lexbuf)
+                        }
+                      });
             }
-            throw exn$4;
+            throw new Error(exn$4.MEL_EXN_ID, {
+                      cause: exn$4
+                    });
           }
       case 19 :
           reset_string_buffer(undefined);
@@ -15786,15 +15941,16 @@ function token(lexbuf) {
       case 26 :
           var l = Stdlib__Lexing.lexeme(lexbuf);
           var esc = Stdlib__String.sub(l, 1, l.length - 1 | 0);
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: {
-                  TAG: /* Illegal_escape */1,
-                  _0: esc
-                },
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: {
+                        TAG: /* Illegal_escape */1,
+                        _0: esc
+                      },
+                      _2: curr(lexbuf)
+                    }
+                  });
       case 27 :
           var match = with_comment_buffer(comment, lexbuf);
           return {
@@ -16003,29 +16159,32 @@ function token(lexbuf) {
             return /* EOF */25;
           }
           if (if_then_else.contents === /* Dir_if_true */0) {
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: /* Unterminated_if */2,
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: /* Unterminated_if */2,
+                        _2: curr(lexbuf)
+                      }
+                    });
           }
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unterminated_else */3,
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unterminated_else */3,
+                      _2: curr(lexbuf)
+                    }
+                  });
       case 91 :
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: {
-                  TAG: /* Illegal_character */0,
-                  _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
-                },
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: {
+                        TAG: /* Illegal_character */0,
+                        _0: Stdlib__Lexing.lexeme_char(lexbuf, 0)
+                      },
+                      _2: curr(lexbuf)
+                    }
+                  });
       default:
         Curry._1(lexbuf.refill_buff, lexbuf);
         ___ocaml_lex_state = __ocaml_lex_state$1;
@@ -16074,12 +16233,13 @@ function string(lexbuf) {
           return string(lexbuf);
       case 7 :
           is_in_string.contents = false;
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unterminated_string */0,
-                _2: string_start_loc.contents,
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unterminated_string */0,
+                      _2: string_start_loc.contents
+                    }
+                  });
       case 8 :
           store_string_char(Stdlib__Lexing.lexeme_char(lexbuf, 0));
           return string(lexbuf);
@@ -16120,15 +16280,16 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
             comment_start_loc.contents = /* [] */0;
             return curr(lexbuf);
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "parsing/lexer.mll",
-                  992,
-                  16
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "parsing/lexer.mll",
+                        992,
+                        16
+                      ]
+                    }
+                  });
       case 2 :
           string_start_loc.contents = curr(lexbuf);
           store_string_char(/* '"' */34);
@@ -16142,36 +16303,44 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
               var match$1 = exn._1;
               if (typeof match$1 === "number") {
                 if (match$1) {
-                  throw exn;
+                  throw new Error(exn.MEL_EXN_ID, {
+                            cause: exn
+                          });
                 }
                 var match$2 = comment_start_loc.contents;
                 if (match$2) {
                   var start = Stdlib__List.hd(Stdlib__List.rev(comment_start_loc.contents));
                   comment_start_loc.contents = /* [] */0;
-                  throw {
-                        MEL_EXN_ID: $$Error$2,
-                        _1: {
-                          TAG: /* Unterminated_string_in_comment */3,
-                          _0: start,
-                          _1: exn._2
-                        },
-                        _2: match$2.hd,
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$2, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$2,
+                              _1: {
+                                TAG: /* Unterminated_string_in_comment */3,
+                                _0: start,
+                                _1: exn._2
+                              },
+                              _2: match$2.hd
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "parsing/lexer.mll",
-                        1006,
-                        18
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "parsing/lexer.mll",
+                              1006,
+                              18
+                            ]
+                          }
+                        });
               }
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
-            throw exn;
+            throw new Error(exn.MEL_EXN_ID, {
+                      cause: exn
+                    });
           }
           is_in_string.contents = false;
           store_string_char(/* '"' */34);
@@ -16192,36 +16361,44 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
               var match$3 = exn$1._1;
               if (typeof match$3 === "number") {
                 if (match$3) {
-                  throw exn$1;
+                  throw new Error(exn$1.MEL_EXN_ID, {
+                            cause: exn$1
+                          });
                 }
                 var match$4 = comment_start_loc.contents;
                 if (match$4) {
                   var start$1 = Stdlib__List.hd(Stdlib__List.rev(comment_start_loc.contents));
                   comment_start_loc.contents = /* [] */0;
-                  throw {
-                        MEL_EXN_ID: $$Error$2,
-                        _1: {
-                          TAG: /* Unterminated_string_in_comment */3,
-                          _0: start$1,
-                          _1: exn$1._2
-                        },
-                        _2: match$4.hd,
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$2, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$2,
+                              _1: {
+                                TAG: /* Unterminated_string_in_comment */3,
+                                _0: start$1,
+                                _1: exn$1._2
+                              },
+                              _2: match$4.hd
+                            }
+                          });
                 }
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "parsing/lexer.mll",
-                        1026,
-                        18
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "parsing/lexer.mll",
+                              1026,
+                              18
+                            ]
+                          }
+                        });
               }
-              throw exn$1;
+              throw new Error(exn$1.MEL_EXN_ID, {
+                        cause: exn$1
+                      });
             }
-            throw exn$1;
+            throw new Error(exn$1.MEL_EXN_ID, {
+                      cause: exn$1
+                    });
           }
           is_in_string.contents = false;
           store_string_char(/* '|' */124);
@@ -16239,25 +16416,27 @@ function __ocaml_lex_comment_rec(lexbuf, ___ocaml_lex_state) {
           if (match$5) {
             var start$2 = Stdlib__List.hd(Stdlib__List.rev(comment_start_loc.contents));
             comment_start_loc.contents = /* [] */0;
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: {
-                    TAG: /* Unterminated_comment */2,
-                    _0: start$2
-                  },
-                  _2: match$5.hd,
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: {
+                          TAG: /* Unterminated_comment */2,
+                          _0: start$2
+                        },
+                        _2: match$5.hd
+                      }
+                    });
           }
-          throw {
-                MEL_EXN_ID: "Assert_failure",
-                _1: [
-                  "parsing/lexer.mll",
-                  1056,
-                  16
-                ],
-                Error: new Error()
-              };
+          throw new Error("Assert_failure", {
+                    cause: {
+                      MEL_EXN_ID: "Assert_failure",
+                      _1: [
+                        "parsing/lexer.mll",
+                        1056,
+                        16
+                      ]
+                    }
+                  });
       case 11 :
           update_loc(lexbuf, undefined, 1, false, 0);
           store_string(Stdlib__Lexing.lexeme(lexbuf));
@@ -16292,12 +16471,13 @@ function __ocaml_lex_quoted_string_rec(delim, lexbuf, ___ocaml_lex_state) {
           continue ;
       case 1 :
           is_in_string.contents = false;
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unterminated_string */0,
-                _2: string_start_loc.contents,
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unterminated_string */0,
+                      _2: string_start_loc.contents
+                    }
+                  });
       case 2 :
           var edelim = Stdlib__Lexing.lexeme(lexbuf);
           var edelim$1 = Stdlib__String.sub(edelim, 1, edelim.length - 2 | 0);
@@ -16360,22 +16540,24 @@ function interpret_directive(lexbuf, cont, look_ahead) {
     switch (match) {
       case /* ELSE */23 :
           if (if_then_else$1) {
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: /* Unexpected_directive */6,
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: /* Unexpected_directive */6,
+                        _2: curr(lexbuf)
+                      }
+                    });
           }
           break;
       case /* END */24 :
           if (if_then_else$1 >= 2) {
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: /* Unexpected_directive */6,
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: /* Unexpected_directive */6,
+                        _2: curr(lexbuf)
+                      }
+                    });
           }
           if_then_else.contents = /* Dir_out */2;
           return Curry._1(cont, lexbuf);
@@ -16389,12 +16571,13 @@ function interpret_directive(lexbuf, cont, look_ahead) {
               while(true) {
                 var token = token_with_comments(lexbuf);
                 if (Caml_obj.caml_equal(token, /* EOF */25)) {
-                  throw {
-                        MEL_EXN_ID: $$Error$2,
-                        _1: /* Unterminated_if */2,
-                        _2: curr(lexbuf),
-                        Error: new Error()
-                      };
+                  throw new Error($$Error$2, {
+                            cause: {
+                              MEL_EXN_ID: $$Error$2,
+                              _1: /* Unterminated_if */2,
+                              _2: curr(lexbuf)
+                            }
+                          });
                 }
                 if (Caml_obj.caml_equal(token, /* SHARP */84) && at_bol(lexbuf)) {
                   var token$1 = token_with_comments(lexbuf);
@@ -16409,12 +16592,13 @@ function interpret_directive(lexbuf, cont, look_ahead) {
                       }
                     }
                     if (token$1 === 37) {
-                      throw {
-                            MEL_EXN_ID: $$Error$2,
-                            _1: /* Unexpected_directive */6,
-                            _2: curr(lexbuf),
-                            Error: new Error()
-                          };
+                      throw new Error($$Error$2, {
+                                cause: {
+                                  MEL_EXN_ID: $$Error$2,
+                                  _1: /* Unexpected_directive */6,
+                                  _2: curr(lexbuf)
+                                }
+                              });
                     }
                     
                   }
@@ -16430,12 +16614,13 @@ function interpret_directive(lexbuf, cont, look_ahead) {
               };
             }
           }
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unexpected_directive */6,
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unexpected_directive */6,
+                      _2: curr(lexbuf)
+                    }
+                  });
       default:
         return Curry._1(look_ahead, match);
     }
@@ -16447,12 +16632,13 @@ function interpret_directive(lexbuf, cont, look_ahead) {
       return Curry._1(look_ahead, match);
     }
     if (if_then_else$1) {
-      throw {
-            MEL_EXN_ID: $$Error$2,
-            _1: /* Unexpected_directive */6,
-            _2: curr(lexbuf),
-            Error: new Error()
-          };
+      throw new Error($$Error$2, {
+                cause: {
+                  MEL_EXN_ID: $$Error$2,
+                  _1: /* Unexpected_directive */6,
+                  _2: curr(lexbuf)
+                }
+              });
     }
     
   }
@@ -16464,12 +16650,13 @@ function interpret_directive(lexbuf, cont, look_ahead) {
     var else_seen = _else_seen;
     var token$2 = token_with_comments(lexbuf);
     if (Caml_obj.caml_equal(token$2, /* EOF */25)) {
-      throw {
-            MEL_EXN_ID: $$Error$2,
-            _1: /* Unterminated_else */3,
-            _2: curr(lexbuf),
-            Error: new Error()
-          };
+      throw new Error($$Error$2, {
+                cause: {
+                  MEL_EXN_ID: $$Error$2,
+                  _1: /* Unterminated_else */3,
+                  _2: curr(lexbuf)
+                }
+              });
     }
     if (Caml_obj.caml_equal(token$2, /* SHARP */84) && at_bol(lexbuf)) {
       var token$3 = token_with_comments(lexbuf);
@@ -16480,33 +16667,36 @@ function interpret_directive(lexbuf, cont, look_ahead) {
             return Curry._1(cont, lexbuf);
           }
           if (else_seen) {
-            throw {
-                  MEL_EXN_ID: $$Error$2,
-                  _1: /* Unexpected_directive */6,
-                  _2: curr(lexbuf),
-                  Error: new Error()
-                };
+            throw new Error($$Error$2, {
+                      cause: {
+                        MEL_EXN_ID: $$Error$2,
+                        _1: /* Unexpected_directive */6,
+                        _2: curr(lexbuf)
+                      }
+                    });
           }
           _else_seen = true;
           continue ;
         }
         if (token$3 === 37) {
-          throw {
-                MEL_EXN_ID: $$Error$2,
-                _1: /* Unexpected_directive */6,
-                _2: curr(lexbuf),
-                Error: new Error()
-              };
+          throw new Error($$Error$2, {
+                    cause: {
+                      MEL_EXN_ID: $$Error$2,
+                      _1: /* Unexpected_directive */6,
+                      _2: curr(lexbuf)
+                    }
+                  });
         }
         
       }
       if (else_seen && is_elif(token$3)) {
-        throw {
-              MEL_EXN_ID: $$Error$2,
-              _1: /* Unexpected_directive */6,
-              _2: curr(lexbuf),
-              Error: new Error()
-            };
+        throw new Error($$Error$2, {
+                  cause: {
+                    MEL_EXN_ID: $$Error$2,
+                    _1: /* Unexpected_directive */6,
+                    _2: curr(lexbuf)
+                  }
+                });
       }
       continue ;
     }
@@ -16765,7 +16955,9 @@ function skip_phrase(lexbuf) {
           if (tmp === /* Unterminated_string */0) {
             continue ;
           }
-          throw exn;
+          throw new Error(exn.MEL_EXN_ID, {
+                    cause: exn
+                  });
         } else {
           switch (tmp.TAG | 0) {
             case /* Illegal_character */0 :
@@ -16773,11 +16965,15 @@ function skip_phrase(lexbuf) {
             case /* Unterminated_string_in_comment */3 :
                 continue ;
             default:
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
           }
         }
       } else {
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
     }
   };
@@ -16805,26 +17001,40 @@ function wrap(parsing_fun, lexbuf) {
     if (err.MEL_EXN_ID === $$Error$2) {
       var tmp = err._1;
       if (typeof tmp === "number") {
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       if (tmp.TAG === /* Illegal_character */0) {
         if (input_name.contents === "//toplevel//") {
           skip_phrase(lexbuf);
-          throw err;
+          throw new Error(err.MEL_EXN_ID, {
+                    cause: err
+                  });
         }
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
-      throw err;
+      throw new Error(err.MEL_EXN_ID, {
+                cause: err
+              });
     } else {
       if (err.MEL_EXN_ID === $$Error$1) {
         if (input_name.contents === "//toplevel//") {
           maybe_skip_phrase(lexbuf);
-          throw err;
+          throw new Error(err.MEL_EXN_ID, {
+                    cause: err
+                  });
         }
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       if (err.MEL_EXN_ID !== Stdlib__Parsing.Parse_error && err.MEL_EXN_ID !== Escape_error) {
-        throw err;
+        throw new Error(err.MEL_EXN_ID, {
+                  cause: err
+                });
       }
       
     }
@@ -16832,14 +17042,15 @@ function wrap(parsing_fun, lexbuf) {
     if (input_name.contents === "//toplevel//") {
       maybe_skip_phrase(lexbuf);
     }
-    throw {
-          MEL_EXN_ID: $$Error$1,
-          _1: {
-            TAG: /* Other */5,
-            _0: loc
-          },
-          Error: new Error()
-        };
+    throw new Error($$Error$1, {
+              cause: {
+                MEL_EXN_ID: $$Error$1,
+                _1: {
+                  TAG: /* Other */5,
+                  _0: loc
+                }
+              }
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/pq_test.js b/jscomp/test/dist/jscomp/test/pq_test.js
index ddf19035d9..739150682e 100644
--- a/jscomp/test/dist/jscomp/test/pq_test.js
+++ b/jscomp/test/dist/jscomp/test/pq_test.js
@@ -63,10 +63,11 @@ function remove_top(param) {
             };
     }
   }
-  throw {
-        MEL_EXN_ID: Queue_is_empty,
-        Error: new Error()
-      };
+  throw new Error(Queue_is_empty, {
+            cause: {
+              MEL_EXN_ID: Queue_is_empty
+            }
+          });
 }
 
 function extract(queue) {
@@ -77,10 +78,11 @@ function extract(queue) {
             remove_top(queue)
           ];
   }
-  throw {
-        MEL_EXN_ID: Queue_is_empty,
-        Error: new Error()
-      };
+  throw new Error(Queue_is_empty, {
+            cause: {
+              MEL_EXN_ID: Queue_is_empty
+            }
+          });
 }
 
 var PrioQueue = {
diff --git a/jscomp/test/dist/jscomp/test/promise_catch_test.js b/jscomp/test/dist/jscomp/test/promise_catch_test.js
index f7be50f658..8d527dbd72 100644
--- a/jscomp/test/dist/jscomp/test/promise_catch_test.js
+++ b/jscomp/test/dist/jscomp/test/promise_catch_test.js
@@ -42,15 +42,16 @@ function handler(e) {
     console.log("hi");
     return Promise.resolve(0);
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/promise_catch_test.ml",
-          21,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/promise_catch_test.ml",
+                21,
+                9
+              ]
+            }
+          });
 }
 
 function myHandler(match) {
@@ -85,15 +86,16 @@ catch (raw_e){
 }
 
 if (exit === 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/promise_catch_test.ml",
-          38,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/promise_catch_test.ml",
+                38,
+                9
+              ]
+            }
+          });
 }
 
 Mt.from_pair_suites("Promise_catch_test", suites.contents);
diff --git a/jscomp/test/dist/jscomp/test/qcc.js b/jscomp/test/dist/jscomp/test/qcc.js
index 76e77a020a..6c72d8b40f 100644
--- a/jscomp/test/dist/jscomp/test/qcc.js
+++ b/jscomp/test/dist/jscomp/test/qcc.js
@@ -42,15 +42,16 @@ function bufferize(f) {
             }),
           (function (x) {
               if (buf.contents !== undefined) {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/qcc.ml",
-                        17,
-                        4
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/qcc.ml",
+                              17,
+                              4
+                            ]
+                          }
+                        });
               }
               buf.contents = Caml_option.some(x);
             })
@@ -100,15 +101,16 @@ function addsym(s) {
 
 function symstr(n) {
   if (n >= syms.contents) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/qcc.ml",
-            40,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/qcc.ml",
+                  40,
+                  4
+                ]
+              }
+            });
   }
   return Caml_array.get(symtab, n);
 }
@@ -196,7 +198,9 @@ function next(param) {
     if (exn.MEL_EXN_ID === Stdlib.End_of_file) {
       c = undefined;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   if (c === undefined) {
@@ -246,11 +250,12 @@ function next(param) {
     var ch = getq(undefined);
     var qt = Curry._1(getch, undefined);
     if (qt !== /* '\'' */39) {
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: "syntax error",
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: "syntax error"
+                }
+              });
     }
     return {
             TAG: /* ILit */1,
@@ -370,15 +375,16 @@ function get32(l) {
 
 function patch(rel, loc, n) {
   if (n >= 0) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/qcc.ml",
-            157,
-            2
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/qcc.ml",
+                  157,
+                  2
+                ]
+              }
+            });
   }
   if (loc === 0) {
     return ;
@@ -964,11 +970,12 @@ function unary(stk) {
                   2
                 ];
               } else {
-                throw {
-                      MEL_EXN_ID: "Failure",
-                      _1: "[cast] expected",
-                      Error: new Error()
-                    };
+                throw new Error("Failure", {
+                          cause: {
+                            MEL_EXN_ID: "Failure",
+                            _1: "[cast] expected"
+                          }
+                        });
               }
               for(var _k = 1 ,_k_finish = match[1]; _k <= _k_finish; ++_k){
                 Curry._1(next$1, undefined);
@@ -1015,11 +1022,12 @@ function unary(stk) {
                         },
                         _1: "unknown operator %s"
                       }), o);
-              throw {
-                    MEL_EXN_ID: "Failure",
-                    _1: s,
-                    Error: new Error()
-                  };
+              throw new Error("Failure", {
+                        cause: {
+                          MEL_EXN_ID: "Failure",
+                          _1: s
+                        }
+                      });
             }
             out(Stdlib__List.assoc(o, unops));
             if (o === "!") {
@@ -1038,15 +1046,16 @@ function unary(stk) {
         if (Stdlib__List.mem_assoc(i$1, stk)) {
           var l = Stdlib__List.assoc(i$1, stk);
           if (l <= -256) {
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/qcc.ml",
-                    295,
-                    6
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/qcc.ml",
+                          295,
+                          6
+                        ]
+                      }
+                    });
           }
           out(4754245);
           out(l & 255);
@@ -1251,11 +1260,12 @@ function decl(g, _n, _stk) {
             if (g) {
               var glo = Caml_array.get(globs, s$1);
               if (glo.va >= 0) {
-                throw {
-                      MEL_EXN_ID: "Failure",
-                      _1: "symbol defined twice",
-                      Error: new Error()
-                    };
+                throw new Error("Failure", {
+                          cause: {
+                            MEL_EXN_ID: "Failure",
+                            _1: "symbol defined twice"
+                          }
+                        });
               }
               var va = (gpos.contents + 232 | 0) + 4194304 | 0;
               Caml_array.set(globs, s$1, {
@@ -1287,11 +1297,12 @@ function decl(g, _n, _stk) {
             _n = n$p;
             continue ;
           }
-          throw {
-                MEL_EXN_ID: "Failure",
-                _1: "[var] expected in [decl]",
-                Error: new Error()
-              };
+          throw new Error("Failure", {
+                    cause: {
+                      MEL_EXN_ID: "Failure",
+                      _1: "[var] expected in [decl]"
+                    }
+                  });
         };
       }
       }(top));
@@ -1324,15 +1335,16 @@ function decl(g, _n, _stk) {
     Curry._1(unnext, t);
     if (!g && n !== 0) {
       if ((n << 3) >= 256) {
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/test/qcc.ml",
-                436,
-                6
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/test/qcc.ml",
+                      436,
+                      6
+                    ]
+                  }
+                });
       }
       out(4752364);
       out((n << 3));
@@ -1452,15 +1464,16 @@ function stmt(brk, stk) {
     var brkl = brk[0];
     var n = align.contents - brk[1] | 0;
     if (n < 0) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/qcc.ml",
-              515,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/qcc.ml",
+                    515,
+                    4
+                  ]
+                }
+              });
     }
     if (n !== 0) {
       out(4752324);
@@ -1525,11 +1538,12 @@ function top(_param) {
       var f$1 = f._0;
       var g = Caml_array.get(globs, f$1);
       if (g.va >= 0) {
-        throw {
-              MEL_EXN_ID: "Failure",
-              _1: "symbol defined twice",
-              Error: new Error()
-            };
+        throw new Error("Failure", {
+                  cause: {
+                    MEL_EXN_ID: "Failure",
+                    _1: "symbol defined twice"
+                  }
+                });
       }
       Caml_array.set(globs, f$1, {
             loc: g.loc,
@@ -1546,18 +1560,20 @@ function top(_param) {
                 if (i._0 === ")") {
                   return stk;
                 }
-                throw {
-                      MEL_EXN_ID: "Failure",
-                      _1: "[var] or ) expected",
-                      Error: new Error()
-                    };
+                throw new Error("Failure", {
+                          cause: {
+                            MEL_EXN_ID: "Failure",
+                            _1: "[var] or ) expected"
+                          }
+                        });
             case /* ILit */1 :
             case /* SLit */2 :
-                throw {
-                      MEL_EXN_ID: "Failure",
-                      _1: "[var] or ) expected",
-                      Error: new Error()
-                    };
+                throw new Error("Failure", {
+                          cause: {
+                            MEL_EXN_ID: "Failure",
+                            _1: "[var] or ) expected"
+                          }
+                        });
             case /* Sym */3 :
                 var r = Stdlib__List.hd(regs);
                 push(r);
@@ -1642,11 +1658,12 @@ function top(_param) {
       _param = undefined;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "[decl] or [fun] expected",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "[decl] or [fun] expected"
+              }
+            });
   };
 }
 
@@ -1869,15 +1886,16 @@ function elfgen(outf) {
   elfphdr(1, 0, tend + off | 0, 2097152);
   elfphdr(2, dyn + off | 0, tend - dyn | 0, 8);
   if (opos.contents !== 232) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/qcc.ml",
-            698,
-            2
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/qcc.ml",
+                  698,
+                  2
+                ]
+              }
+            });
   }
   patch(false, 24, va(entry));
   Stdlib.output_bytes(outf, Stdlib__Bytes.sub(obuf, 0, tend + off | 0));
diff --git a/jscomp/test/dist/jscomp/test/raw_hash_tbl_bench.js b/jscomp/test/dist/jscomp/test/raw_hash_tbl_bench.js
index 3e676da498..2721de4ced 100644
--- a/jscomp/test/dist/jscomp/test/raw_hash_tbl_bench.js
+++ b/jscomp/test/dist/jscomp/test/raw_hash_tbl_bench.js
@@ -10,15 +10,16 @@ function bench(param) {
   }
   for(var i$1 = 0; i$1 <= 1000000; ++i$1){
     if (!Stdlib__Hashtbl.mem(table, i$1)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/raw_hash_tbl_bench.ml",
-              9,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/raw_hash_tbl_bench.ml",
+                    9,
+                    4
+                  ]
+                }
+              });
     }
     
   }
diff --git a/jscomp/test/dist/jscomp/test/rbset.js b/jscomp/test/dist/jscomp/test/rbset.js
index 366a76d1ff..db9c51e777 100644
--- a/jscomp/test/dist/jscomp/test/rbset.js
+++ b/jscomp/test/dist/jscomp/test/rbset.js
@@ -253,15 +253,16 @@ function unbalanced_left(param) {
       
     }
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/rbset.ml",
-          57,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/rbset.ml",
+                57,
+                9
+              ]
+            }
+          });
 }
 
 function unbalanced_right(param) {
@@ -318,15 +319,16 @@ function unbalanced_right(param) {
       
     }
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/rbset.ml",
-          63,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/rbset.ml",
+                63,
+                9
+              ]
+            }
+          });
 }
 
 function lbalance(x1, x2, x3) {
@@ -553,15 +555,16 @@ function remove_min(param) {
                 false
               ];
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/rbset.ml",
-              115,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/rbset.ml",
+                    115,
+                    4
+                  ]
+                }
+              });
     }
     var match$1 = remove_min(param._1);
     var y = match$1[1];
@@ -588,15 +591,16 @@ function remove_min(param) {
             match$2[1]
           ];
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/rbset.ml",
-          115,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/rbset.ml",
+                115,
+                4
+              ]
+            }
+          });
 }
 
 function remove_aux(x, n) {
diff --git a/jscomp/test/dist/jscomp/test/re_or_res/reactDOMRe.js b/jscomp/test/dist/jscomp/test/re_or_res/reactDOMRe.js
index f6430e5183..445a0ba249 100644
--- a/jscomp/test/dist/jscomp/test/re_or_res/reactDOMRe.js
+++ b/jscomp/test/dist/jscomp/test/re_or_res/reactDOMRe.js
@@ -70,11 +70,12 @@ function hydrateToElementWithClassName(reactElement, className) {
 function hydrateToElementWithId(reactElement, id) {
   var element = document.getElementById(id);
   if (element == null) {
-    throw {
-          MEL_EXN_ID: Stdlib.Invalid_argument,
-          _1: "ReactDOMRe.hydrateToElementWithId : no element of id " + (id + " found in the HTML."),
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Invalid_argument, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Invalid_argument,
+                _1: "ReactDOMRe.hydrateToElementWithId : no element of id " + (id + " found in the HTML.")
+              }
+            });
   }
   ReactDom.hydrate(reactElement, element);
 }
diff --git a/jscomp/test/dist/jscomp/test/re_or_res/reactjs_ppx_custom.js b/jscomp/test/dist/jscomp/test/re_or_res/reactjs_ppx_custom.js
index 433b2a5c41..99630400e6 100644
--- a/jscomp/test/dist/jscomp/test/re_or_res/reactjs_ppx_custom.js
+++ b/jscomp/test/dist/jscomp/test/re_or_res/reactjs_ppx_custom.js
@@ -4,15 +4,16 @@
 var JsxRuntime = require("react/jsx-runtime");
 
 function Reactjs_ppx_custom$Internal$header(Props) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/re_or_res/reactjs_ppx_custom.re",
-          4,
-          21
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/re_or_res/reactjs_ppx_custom.re",
+                4,
+                21
+              ]
+            }
+          });
 }
 
 var Internal = {
diff --git a/jscomp/test/dist/jscomp/test/re_or_res/reasonReact.js b/jscomp/test/dist/jscomp/test/re_or_res/reasonReact.js
index 6baf04f102..601c9dbbdf 100644
--- a/jscomp/test/dist/jscomp/test/re_or_res/reasonReact.js
+++ b/jscomp/test/dist/jscomp/test/re_or_res/reasonReact.js
@@ -49,11 +49,12 @@ function convertPropsIfTheyreFromJs(props, jsPropsToReason, debugName) {
             _0: jsPropsToReason(props)
           };
   }
-  throw {
-        MEL_EXN_ID: Stdlib.Invalid_argument,
-        _1: "A JS component called the Reason component " + (debugName + " which didn't implement the JS->Reason React props conversion."),
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Invalid_argument, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Invalid_argument,
+              _1: "A JS component called the Reason component " + (debugName + " which didn't implement the JS->Reason React props conversion.")
+            }
+          });
 }
 
 function createClass(debugName) {
diff --git a/jscomp/test/dist/jscomp/test/rec_module_test.js b/jscomp/test/dist/jscomp/test/rec_module_test.js
index 8310807659..dc72ead1db 100644
--- a/jscomp/test/dist/jscomp/test/rec_module_test.js
+++ b/jscomp/test/dist/jscomp/test/rec_module_test.js
@@ -131,17 +131,19 @@ function bal(l, v, r) {
       if (lr) {
         return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -161,17 +163,19 @@ function bal(l, v, r) {
     if (rl) {
       return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add(x, t) {
@@ -260,10 +264,11 @@ function min_elt(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -292,10 +297,11 @@ function max_elt(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -322,11 +328,12 @@ function remove_min_elt(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.remove_min_elt"
+            }
+          });
 }
 
 function concat(t1, t2) {
@@ -808,10 +815,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -842,10 +850,11 @@ function find_first(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -907,10 +916,11 @@ function find_last(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1125,15 +1135,16 @@ function of_list(l) {
                   match$4[1]
                 ];
         }
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/stdlib/set.ml",
-                571,
-                18
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/stdlib/set.ml",
+                      571,
+                      18
+                    ]
+                  }
+                });
       };
       return sub(Stdlib__List.length(l$1), l$1)[0];
     } else {
diff --git a/jscomp/test/dist/jscomp/test/rec_value_test.js b/jscomp/test/dist/jscomp/test/rec_value_test.js
index cb439b2f99..7c94e5f60b 100644
--- a/jscomp/test/dist/jscomp/test/rec_value_test.js
+++ b/jscomp/test/dist/jscomp/test/rec_value_test.js
@@ -80,15 +80,16 @@ var h = {
 
 var v = {
   contents: (function (param) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/rec_value_test.ml",
-              36,
-              24
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/rec_value_test.ml",
+                    36,
+                    24
+                  ]
+                }
+              });
     })
 };
 
@@ -245,54 +246,58 @@ var rec_variant_a = {
 
 function phd(l) {
   if (typeof l === "string") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/rec_value_test.ml",
-            107,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/rec_value_test.ml",
+                  107,
+                  9
+                ]
+              }
+            });
   }
   if (l.NAME === "Cons") {
     return l.VAL[0];
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/rec_value_test.ml",
-          107,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/rec_value_test.ml",
+                107,
+                9
+              ]
+            }
+          });
 }
 
 function ptl(l) {
   if (typeof l === "string") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/rec_value_test.ml",
-            112,
-            9
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/rec_value_test.ml",
+                  112,
+                  9
+                ]
+              }
+            });
   }
   if (l.NAME === "Cons") {
     return l.VAL[1];
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/rec_value_test.ml",
-          112,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/rec_value_test.ml",
+                112,
+                9
+              ]
+            }
+          });
 }
 
 var y00 = {};
@@ -354,26 +359,28 @@ var suites_1 = {
               if (match) {
                 tmp = match.hd;
               } else {
-                throw {
-                      MEL_EXN_ID: "Assert_failure",
-                      _1: [
-                        "jscomp/test/rec_value_test.ml",
-                        142,
-                        2
-                      ],
-                      Error: new Error()
-                    };
+                throw new Error("Assert_failure", {
+                          cause: {
+                            MEL_EXN_ID: "Assert_failure",
+                            _1: [
+                              "jscomp/test/rec_value_test.ml",
+                              142,
+                              2
+                            ]
+                          }
+                        });
               }
             } else {
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/rec_value_test.ml",
-                      142,
-                      2
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/rec_value_test.ml",
+                            142,
+                            2
+                          ]
+                        }
+                      });
             }
             return {
                     TAG: /* Eq */0,
@@ -509,15 +516,16 @@ var suites_1 = {
                                       _1: rec_variant_a
                                     };
                             }
-                            throw {
-                                  MEL_EXN_ID: "Assert_failure",
-                                  _1: [
-                                    "jscomp/test/rec_value_test.ml",
-                                    166,
-                                    11
-                                  ],
-                                  Error: new Error()
-                                };
+                            throw new Error("Assert_failure", {
+                                      cause: {
+                                        MEL_EXN_ID: "Assert_failure",
+                                        _1: [
+                                          "jscomp/test/rec_value_test.ml",
+                                          166,
+                                          11
+                                        ]
+                                      }
+                                    });
                           })
                       ],
                       tl: {
@@ -531,15 +539,16 @@ var suites_1 = {
                                         _1: rec_variant_b
                                       };
                               }
-                              throw {
-                                    MEL_EXN_ID: "Assert_failure",
-                                    _1: [
-                                      "jscomp/test/rec_value_test.ml",
-                                      171,
-                                      11
-                                    ],
-                                    Error: new Error()
-                                  };
+                              throw new Error("Assert_failure", {
+                                        cause: {
+                                          MEL_EXN_ID: "Assert_failure",
+                                          _1: [
+                                            "jscomp/test/rec_value_test.ml",
+                                            171,
+                                            11
+                                          ]
+                                        }
+                                      });
                             })
                         ],
                         tl: /* [] */0
diff --git a/jscomp/test/dist/jscomp/test/recursive_module.js b/jscomp/test/dist/jscomp/test/recursive_module.js
index e94a34c493..1e088d812b 100644
--- a/jscomp/test/dist/jscomp/test/recursive_module.js
+++ b/jscomp/test/dist/jscomp/test/recursive_module.js
@@ -116,7 +116,9 @@ catch (raw_exn){
   if (exn.MEL_EXN_ID === Stdlib__Lazy.Undefined) {
     tmp = -1;
   } else {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -196,7 +198,9 @@ catch (raw_exn$1){
   if (exn$1.MEL_EXN_ID === Stdlib.Undefined_recursive_module) {
     tmp$1 = 4;
   } else {
-    throw exn$1;
+    throw new Error(exn$1.MEL_EXN_ID, {
+              cause: exn$1
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/recursive_records_test.js b/jscomp/test/dist/jscomp/test/recursive_records_test.js
index 7b2309a37b..4da10953f1 100644
--- a/jscomp/test/dist/jscomp/test/recursive_records_test.js
+++ b/jscomp/test/dist/jscomp/test/recursive_records_test.js
@@ -67,15 +67,16 @@ function tl_exn(x) {
   if (x) {
     return x.next;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/recursive_records_test.ml",
-          52,
-          11
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/recursive_records_test.ml",
+                52,
+                11
+              ]
+            }
+          });
 }
 
 eq("File \"jscomp/test/recursive_records_test.ml\", line 56, characters 6-13", (hd(rec_cell2) + hd(tl_exn(rec_cell2)) | 0) + hd(tl_exn(tl_exn(rec_cell2))) | 0, 9);
diff --git a/jscomp/test/dist/jscomp/test/return_check.js b/jscomp/test/dist/jscomp/test/return_check.js
index 3c98621c43..1cdede5450 100644
--- a/jscomp/test/dist/jscomp/test/return_check.js
+++ b/jscomp/test/dist/jscomp/test/return_check.js
@@ -18,15 +18,16 @@ function f_undefined(xs, i) {
   if (k !== undefined) {
     return k;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/return_check.ml",
-          30,
-          14
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/return_check.ml",
+                30,
+                14
+              ]
+            }
+          });
 }
 
 function f_escaped_not(xs, i) {
@@ -59,15 +60,16 @@ function f_null(xs, i) {
   if (k !== null) {
     return k;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/return_check.ml",
-          58,
-          14
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/return_check.ml",
+                58,
+                14
+              ]
+            }
+          });
 }
 
 function f_null_undefined(xs, i) {
@@ -75,15 +77,16 @@ function f_null_undefined(xs, i) {
   if (!(k == null)) {
     return k;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/return_check.ml",
-          67,
-          14
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/return_check.ml",
+                67,
+                14
+              ]
+            }
+          });
 }
 
 exports.test = test;
diff --git a/jscomp/test/dist/jscomp/test/scanf_io.js b/jscomp/test/dist/jscomp/test/scanf_io.js
index 068292e3a2..71a532ff2d 100644
--- a/jscomp/test/dist/jscomp/test/scanf_io.js
+++ b/jscomp/test/dist/jscomp/test/scanf_io.js
@@ -123,11 +123,12 @@ function get_lines(fname) {
                 },
                 _1: "in file %s, %s"
               }), fname, exn._1);
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: s,
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: s
+                }
+              });
     }
     if (exn.MEL_EXN_ID === Stdlib.End_of_file) {
       var s$1 = Curry._1(Stdlib__Printf.sprintf(/* Format */{
@@ -146,13 +147,16 @@ function get_lines(fname) {
                 },
                 _1: "in file %s, unexpected end of file"
               }), fname);
-      throw {
-            MEL_EXN_ID: "Failure",
-            _1: s$1,
-            Error: new Error()
-          };
+      throw new Error("Failure", {
+                cause: {
+                  MEL_EXN_ID: "Failure",
+                  _1: s$1
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -190,7 +194,9 @@ function add_digest_ib(ob, ib) {
     if (exn.MEL_EXN_ID === Stdlib.End_of_file) {
       return ;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/scanf_reference_error_regression_test.js b/jscomp/test/dist/jscomp/test/scanf_reference_error_regression_test.js
index bf8d35bed0..3b2e459a34 100644
--- a/jscomp/test/dist/jscomp/test/scanf_reference_error_regression_test.js
+++ b/jscomp/test/dist/jscomp/test/scanf_reference_error_regression_test.js
@@ -78,11 +78,12 @@ function scan_rest(ib, accu) {
                                                         },
                                                         _1: "scan_int_list"
                                                       });
-                                                  throw {
-                                                        MEL_EXN_ID: "Failure",
-                                                        _1: s,
-                                                        Error: new Error()
-                                                      };
+                                                  throw new Error("Failure", {
+                                                            cause: {
+                                                              MEL_EXN_ID: "Failure",
+                                                              _1: s
+                                                            }
+                                                          });
                                               }
                                             }));
                               }));
diff --git a/jscomp/test/dist/jscomp/test/set_gen.js b/jscomp/test/dist/jscomp/test/set_gen.js
index 6c2933a162..9539c66fe1 100644
--- a/jscomp/test/dist/jscomp/test/set_gen.js
+++ b/jscomp/test/dist/jscomp/test/set_gen.js
@@ -43,10 +43,11 @@ function min_elt(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -60,10 +61,11 @@ function max_elt(_param) {
       _param = param._2;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -206,17 +208,19 @@ function check_height_and_diff(param) {
   var hl = check_height_and_diff(param._0);
   var hr = check_height_and_diff(param._2);
   if (h !== (max_int_2(hl, hr) + 1 | 0)) {
-    throw {
-          MEL_EXN_ID: Height_invariant_broken,
-          Error: new Error()
-        };
+    throw new Error(Height_invariant_broken, {
+              cause: {
+                MEL_EXN_ID: Height_invariant_broken
+              }
+            });
   }
   var diff = Stdlib.abs(hl - hr | 0);
   if (diff > 2) {
-    throw {
-          MEL_EXN_ID: Height_diff_borken,
-          Error: new Error()
-        };
+    throw new Error(Height_diff_borken, {
+              cause: {
+                MEL_EXN_ID: Height_diff_borken
+              }
+            });
   }
   return h;
 }
@@ -250,25 +254,27 @@ function internal_bal(l, v, r) {
       if (lr) {
         return create(create(ll, lv, lr._0), lr._1, create(lr._2, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/set_gen.ml",
-              235,
-              19
-            ],
-            Error: new Error()
-          };
-    }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/set_gen.ml",
-            225,
-            15
-          ],
-          Error: new Error()
-        };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/set_gen.ml",
+                    235,
+                    19
+                  ]
+                }
+              });
+    }
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/set_gen.ml",
+                  225,
+                  15
+                ]
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -288,25 +294,27 @@ function internal_bal(l, v, r) {
     if (rl) {
       return create(create(l, v, rl._0), rl._1, create(rl._2, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/set_gen.ml",
-            251,
-            19
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/set_gen.ml",
+                  251,
+                  19
+                ]
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/set_gen.ml",
-          245,
-          15
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/set_gen.ml",
+                245,
+                15
+              ]
+            }
+          });
 }
 
 function remove_min_elt(param) {
@@ -318,11 +326,12 @@ function remove_min_elt(param) {
       return param._2;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.remove_min_elt"
+            }
+          });
 }
 
 function singleton(x) {
@@ -522,15 +531,16 @@ function of_sorted_list(l) {
               match$4[1]
             ];
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/set_gen.ml",
-            361,
-            14
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/set_gen.ml",
+                  361,
+                  14
+                ]
+              }
+            });
   };
   return sub(Stdlib__List.length(l), l)[0];
 }
diff --git a/jscomp/test/dist/jscomp/test/sexp.js b/jscomp/test/dist/jscomp/test/sexp.js
index 14a9c02ca7..8e8dd2d386 100644
--- a/jscomp/test/dist/jscomp/test/sexp.js
+++ b/jscomp/test/dist/jscomp/test/sexp.js
@@ -486,11 +486,12 @@ function get_exn(e) {
   if (e !== undefined) {
     return Caml_option.valFromOption(e);
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "CCSexp.Traverse.get_exn",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "CCSexp.Traverse.get_exn"
+            }
+          });
 }
 
 var of_unit = {
diff --git a/jscomp/test/dist/jscomp/test/sexpm.js b/jscomp/test/dist/jscomp/test/sexpm.js
index 5ed1db55dc..01d59121e2 100644
--- a/jscomp/test/dist/jscomp/test/sexpm.js
+++ b/jscomp/test/dist/jscomp/test/sexpm.js
@@ -45,16 +45,18 @@ function _must_escape(s) {
           if (c !== 92) {
             exit = 1;
           } else {
-            throw {
-                  MEL_EXN_ID: Stdlib.Exit,
-                  Error: new Error()
-                };
+            throw new Error(Stdlib.Exit, {
+                      cause: {
+                        MEL_EXN_ID: Stdlib.Exit
+                      }
+                    });
           }
         } else {
-          throw {
-                MEL_EXN_ID: Stdlib.Exit,
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Exit, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Exit
+                    }
+                  });
         }
       } else if (c >= 11) {
         if (c >= 32) {
@@ -71,10 +73,11 @@ function _must_escape(s) {
             case 34 :
             case 40 :
             case 41 :
-                throw {
-                      MEL_EXN_ID: Stdlib.Exit,
-                      Error: new Error()
-                    };
+                throw new Error(Stdlib.Exit, {
+                          cause: {
+                            MEL_EXN_ID: Stdlib.Exit
+                          }
+                        });
             
           }
         } else {
@@ -82,18 +85,20 @@ function _must_escape(s) {
         }
       } else {
         if (c >= 9) {
-          throw {
-                MEL_EXN_ID: Stdlib.Exit,
-                Error: new Error()
-              };
+          throw new Error(Stdlib.Exit, {
+                    cause: {
+                      MEL_EXN_ID: Stdlib.Exit
+                    }
+                  });
         }
         exit = 1;
       }
       if (exit === 1 && c > 127) {
-        throw {
-              MEL_EXN_ID: Stdlib.Exit,
-              Error: new Error()
-            };
+        throw new Error(Stdlib.Exit, {
+                  cause: {
+                    MEL_EXN_ID: Stdlib.Exit
+                  }
+                });
       }
       
     }
@@ -104,7 +109,9 @@ function _must_escape(s) {
     if (exn.MEL_EXN_ID === Stdlib.Exit) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -370,7 +377,9 @@ function to_file_seq(filename, seq) {
   catch (e){
     Caml_io.caml_ml_flush(oc);
     Caml_external_polyfill.resolve("caml_ml_close_channel")(oc);
-    throw e;
+    throw new Error(e.MEL_EXN_ID, {
+              cause: e
+            });
   }
 }
 
@@ -428,15 +437,16 @@ function _refill(t, k_succ, k_fail) {
 
 function _get(t) {
   if (t.i >= t.len) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/sexpm.ml",
-            152,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/sexpm.ml",
+                  152,
+                  4
+                ]
+              }
+            });
   }
   var c = Caml_bytes.get(t.buf, t.i);
   t.i = t.i + 1 | 0;
@@ -542,15 +552,16 @@ function expr_starting_with(c, k, t) {
     if (c >= 32) {
       switch (c) {
         case 32 :
-            throw {
-                  MEL_EXN_ID: "Assert_failure",
-                  _1: [
-                    "jscomp/test/sexpm.ml",
-                    183,
-                    27
-                  ],
-                  Error: new Error()
-                };
+            throw new Error("Assert_failure", {
+                      cause: {
+                        MEL_EXN_ID: "Assert_failure",
+                        _1: [
+                          "jscomp/test/sexpm.ml",
+                          183,
+                          27
+                        ]
+                      }
+                    });
         case 34 :
             return quoted(k, t);
         case 33 :
@@ -576,15 +587,16 @@ function expr_starting_with(c, k, t) {
     }
     
   } else if (c >= 9) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/sexpm.ml",
-            183,
-            27
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/sexpm.ml",
+                  183,
+                  27
+                ]
+              }
+            });
   }
   Stdlib__Buffer.add_char(t.atom, c);
   return atom(k, t);
@@ -1040,15 +1052,16 @@ function MakeDecode(funarg) {
   };
   var _get = function (t) {
     if (t.i >= t.len) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/sexpm.ml",
-              152,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/sexpm.ml",
+                    152,
+                    4
+                  ]
+                }
+              });
     }
     var c = Caml_bytes.get(t.buf, t.i);
     t.i = t.i + 1 | 0;
@@ -1150,15 +1163,16 @@ function MakeDecode(funarg) {
       if (c >= 32) {
         switch (c) {
           case 32 :
-              throw {
-                    MEL_EXN_ID: "Assert_failure",
-                    _1: [
-                      "jscomp/test/sexpm.ml",
-                      183,
-                      27
-                    ],
-                    Error: new Error()
-                  };
+              throw new Error("Assert_failure", {
+                        cause: {
+                          MEL_EXN_ID: "Assert_failure",
+                          _1: [
+                            "jscomp/test/sexpm.ml",
+                            183,
+                            27
+                          ]
+                        }
+                      });
           case 34 :
               return quoted(k, t);
           case 33 :
@@ -1184,15 +1198,16 @@ function MakeDecode(funarg) {
       }
       
     } else if (c >= 9) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/sexpm.ml",
-              183,
-              27
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/sexpm.ml",
+                    183,
+                    27
+                  ]
+                }
+              });
     }
     Stdlib__Buffer.add_char(t.atom, c);
     return atom(k, t);
diff --git a/jscomp/test/dist/jscomp/test/stack_comp_test.js b/jscomp/test/dist/jscomp/test/stack_comp_test.js
index 4f0c56b6bb..323e186e34 100644
--- a/jscomp/test/dist/jscomp/test/stack_comp_test.js
+++ b/jscomp/test/dist/jscomp/test/stack_comp_test.js
@@ -72,7 +72,9 @@ function does_raise(f, s) {
     if (exn.MEL_EXN_ID === Stdlib__Stack.Empty) {
       return true;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/stdlib_bytes_utf8_test.js b/jscomp/test/dist/jscomp/test/stdlib_bytes_utf8_test.js
index a6408b79ef..2fc3c960f2 100644
--- a/jscomp/test/dist/jscomp/test/stdlib_bytes_utf8_test.js
+++ b/jscomp/test/dist/jscomp/test/stdlib_bytes_utf8_test.js
@@ -335,15 +335,16 @@ function uchar_map_of_spec(spec) {
     if ((uchar.contents - 1 | 0) === match[1]) {
       return ;
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/stdlib_bytes_utf8_test.ml",
-            69,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/stdlib_bytes_utf8_test.ml",
+                  69,
+                  4
+                ]
+              }
+            });
   };
   Stdlib__List.iter(add_range, spec);
   return map;
@@ -377,82 +378,89 @@ function test_utf(utf, utf_len, get_utf, set_utf, utf_is_valid) {
     var utf_len$1 = Curry._1(utf_len, u);
     var buf = Caml_bytes.caml_create_bytes(utf_len$1);
     if (Curry._3(set_utf, buf, 0, u) !== utf_len$1) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              97,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    97,
+                    4
+                  ]
+                }
+              });
     }
     if (!Caml_bytes.caml_bytes_equal(buf, Caml_array.get(utf, u))) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              98,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    98,
+                    4
+                  ]
+                }
+              });
     }
     if (!Caml_bytes.caml_bytes_equal(buf, Caml_array.get(utf, u))) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              99,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    99,
+                    4
+                  ]
+                }
+              });
     }
     var dec = Curry._2(get_utf, buf, 0);
     if ((dec >>> 27) !== 1) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              101,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    101,
+                    4
+                  ]
+                }
+              });
     }
     if (((dec >>> 24) & 7) !== utf_len$1) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              102,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    102,
+                    4
+                  ]
+                }
+              });
     }
     if ((dec & 16777215) !== u) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              103,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    103,
+                    4
+                  ]
+                }
+              });
     }
     if (!Curry._1(utf_is_valid, buf)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              104,
-              4
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    104,
+                    4
+                  ]
+                }
+              });
     }
     
   };
@@ -476,21 +484,24 @@ function raises(f) {
     if (exn.MEL_EXN_ID === Stdlib.Invalid_argument) {
       tmp = true;
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   if (tmp) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          124,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                124,
+                4
+              ]
+            }
+          });
 }
 
 raises(function (param) {
@@ -520,39 +531,42 @@ raises(function (param) {
 var b = Stdlib__Bytes.make(1, /* '\171' */171);
 
 if (!(Stdlib__Bytes.set_utf_8_uchar(b, 0, Stdlib__Uchar.max) === 0 && Caml_bytes.get(b, 0) === /* '\171' */171)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          141,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                141,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Stdlib__Bytes.set_utf_16be_uchar(b, 0, Stdlib__Uchar.max) === 0 && Caml_bytes.get(b, 0) === /* '\171' */171)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          142,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                142,
+                2
+              ]
+            }
+          });
 }
 
 if (!(Stdlib__Bytes.set_utf_16le_uchar(b, 0, Stdlib__Uchar.max) === 0 && Caml_bytes.get(b, 0) === /* '\171' */171)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          143,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                143,
+                2
+              ]
+            }
+          });
 }
 
 var b$1 = [
@@ -565,15 +579,16 @@ Caml_bytes.set(b$1, 0, 195);
 Caml_bytes.set(b$1, 1, 0);
 
 if (Stdlib__Bytes.is_valid_utf_8(b$1)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          151,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                151,
+                2
+              ]
+            }
+          });
 }
 
 var b$2 = Stdlib__Bytes.of_string("\xc0\xaf\xe0\x80\xbf\xf0\x81\x82A");
@@ -586,72 +601,78 @@ for(var i = 0 ,i_finish = b$2.length; i < i_finish; ++i){
   var dec = Stdlib__Bytes.get_utf_8_uchar(b$2, i);
   if (ok(i)) {
     if ((dec >>> 27) === 1 !== true) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              166,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    166,
+                    6
+                  ]
+                }
+              });
     }
     if (((dec >>> 24) & 7) !== 1) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              167,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    167,
+                    6
+                  ]
+                }
+              });
     }
     if ((dec & 16777215) !== Stdlib__Uchar.of_int(65)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              168,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    168,
+                    6
+                  ]
+                }
+              });
     }
     
   } else {
     if ((dec >>> 27) === 1 !== false) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              162,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    162,
+                    6
+                  ]
+                }
+              });
     }
     if (((dec >>> 24) & 7) !== 1) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              163,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    163,
+                    6
+                  ]
+                }
+              });
     }
     if ((dec & 16777215) !== Stdlib__Uchar.rep) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              164,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    164,
+                    6
+                  ]
+                }
+              });
     }
     
   }
@@ -667,72 +688,78 @@ for(var i$1 = 0 ,i_finish$1 = b$3.length; i$1 < i_finish$1; ++i$1){
   var dec$1 = Stdlib__Bytes.get_utf_8_uchar(b$3, i$1);
   if (ok$1(i$1)) {
     if ((dec$1 >>> 27) === 1 !== true) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              179,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    179,
+                    6
+                  ]
+                }
+              });
     }
     if (((dec$1 >>> 24) & 7) !== 1) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              180,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    180,
+                    6
+                  ]
+                }
+              });
     }
     if ((dec$1 & 16777215) !== Stdlib__Uchar.of_int(65)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              181,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    181,
+                    6
+                  ]
+                }
+              });
     }
     
   } else {
     if ((dec$1 >>> 27) === 1 !== false) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              175,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    175,
+                    6
+                  ]
+                }
+              });
     }
     if (((dec$1 >>> 24) & 7) !== 1) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              176,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    176,
+                    6
+                  ]
+                }
+              });
     }
     if ((dec$1 & 16777215) !== Stdlib__Uchar.rep) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              177,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    177,
+                    6
+                  ]
+                }
+              });
     }
     
   }
@@ -752,72 +779,78 @@ for(var i$2 = 0 ,i_finish$2 = b$4.length; i$2 < i_finish$2; ++i$2){
   var dec$2 = Stdlib__Bytes.get_utf_8_uchar(b$4, i$2);
   if (ok$2(i$2)) {
     if ((dec$2 >>> 27) === 1 !== true) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              192,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    192,
+                    6
+                  ]
+                }
+              });
     }
     if (((dec$2 >>> 24) & 7) !== 1) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              193,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    193,
+                    6
+                  ]
+                }
+              });
     }
     if ((dec$2 & 16777215) !== Caml_bytes.get(b$4, i$2)) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              194,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    194,
+                    6
+                  ]
+                }
+              });
     }
     
   } else {
     if ((dec$2 >>> 27) === 1 !== false) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              188,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    188,
+                    6
+                  ]
+                }
+              });
     }
     if (((dec$2 >>> 24) & 7) !== 1) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              189,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    189,
+                    6
+                  ]
+                }
+              });
     }
     if ((dec$2 & 16777215) !== Stdlib__Uchar.rep) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/stdlib_bytes_utf8_test.ml",
-              190,
-              6
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/stdlib_bytes_utf8_test.ml",
+                    190,
+                    6
+                  ]
+                }
+              });
     }
     
   }
@@ -828,179 +861,193 @@ var b$5 = Stdlib__Bytes.of_string("\xe1\x80\xe2\xf0\x91\x92\xf1\xbfA");
 var d0 = Stdlib__Bytes.get_utf_8_uchar(b$5, 0);
 
 if ((d0 >>> 27) === 1 !== false) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          199,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                199,
+                2
+              ]
+            }
+          });
 }
 
 if (((d0 >>> 24) & 7) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          200,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                200,
+                2
+              ]
+            }
+          });
 }
 
 if ((d0 & 16777215) !== Stdlib__Uchar.rep) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          201,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                201,
+                2
+              ]
+            }
+          });
 }
 
 var d2 = Stdlib__Bytes.get_utf_8_uchar(b$5, 2);
 
 if ((d2 >>> 27) === 1 !== false) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          203,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                203,
+                2
+              ]
+            }
+          });
 }
 
 if (((d2 >>> 24) & 7) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          204,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                204,
+                2
+              ]
+            }
+          });
 }
 
 if ((d2 & 16777215) !== Stdlib__Uchar.rep) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          205,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                205,
+                2
+              ]
+            }
+          });
 }
 
 var d3 = Stdlib__Bytes.get_utf_8_uchar(b$5, 3);
 
 if ((d3 >>> 27) === 1 !== false) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          207,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                207,
+                2
+              ]
+            }
+          });
 }
 
 if (((d3 >>> 24) & 7) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          208,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                208,
+                2
+              ]
+            }
+          });
 }
 
 if ((d3 & 16777215) !== Stdlib__Uchar.rep) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          209,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                209,
+                2
+              ]
+            }
+          });
 }
 
 var d6 = Stdlib__Bytes.get_utf_8_uchar(b$5, 6);
 
 if ((d6 >>> 27) === 1 !== false) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          211,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                211,
+                2
+              ]
+            }
+          });
 }
 
 if (((d6 >>> 24) & 7) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          212,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                212,
+                2
+              ]
+            }
+          });
 }
 
 if ((d6 & 16777215) !== Stdlib__Uchar.rep) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          213,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                213,
+                2
+              ]
+            }
+          });
 }
 
 var d8 = Stdlib__Bytes.get_utf_8_uchar(b$5, 8);
 
 if (((d8 >>> 24) & 7) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          215,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                215,
+                2
+              ]
+            }
+          });
 }
 
 if ((d8 & 16777215) !== Stdlib__Uchar.of_int(65)) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stdlib_bytes_utf8_test.ml",
-          216,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stdlib_bytes_utf8_test.ml",
+                216,
+                2
+              ]
+            }
+          });
 }
 
 Stdlib__Printf.printf(/* Format */{
diff --git a/jscomp/test/dist/jscomp/test/string_set.js b/jscomp/test/dist/jscomp/test/string_set.js
index e94cf4c2c3..eddfc00e59 100644
--- a/jscomp/test/dist/jscomp/test/string_set.js
+++ b/jscomp/test/dist/jscomp/test/string_set.js
@@ -229,10 +229,11 @@ function find(x, _tree) {
       _tree = c < 0 ? tree._0 : tree._2;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/string_test.js b/jscomp/test/dist/jscomp/test/string_test.js
index d30bb42a9f..0062fed092 100644
--- a/jscomp/test/dist/jscomp/test/string_test.js
+++ b/jscomp/test/dist/jscomp/test/string_test.js
@@ -79,7 +79,9 @@ function rev_split_by_char(c, s) {
                 tl: l
               };
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   };
   return loop(0, /* [] */0);
@@ -108,7 +110,9 @@ function xsplit(delim, s) {
                   tl: l
                 };
         }
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
       var l_0 = Stdlib__String.sub(s, i$p + 1 | 0, (i - i$p | 0) - 1 | 0);
       var l$1 = {
diff --git a/jscomp/test/dist/jscomp/test/stringmatch_test.js b/jscomp/test/dist/jscomp/test/stringmatch_test.js
index eeadaca02b..f918cc6cd1 100644
--- a/jscomp/test/dist/jscomp/test/stringmatch_test.js
+++ b/jscomp/test/dist/jscomp/test/stringmatch_test.js
@@ -11,39 +11,42 @@ function tst01(s) {
 }
 
 if (tst01("") !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          20,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                20,
+                2
+              ]
+            }
+          });
 }
 
 if (tst01("\0\0\0\x03") !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          21,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                21,
+                2
+              ]
+            }
+          });
 }
 
 if (tst01("\0\0\0\0\0\0\0\x07") !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          22,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                22,
+                2
+              ]
+            }
+          });
 }
 
 function tst02(s) {
@@ -52,26 +55,28 @@ function tst02(s) {
     if (len >= 0) {
       return 1;
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/stringmatch_test.ml",
-            30,
-            23
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/stringmatch_test.ml",
+                  30,
+                  23
+                ]
+              }
+            });
   }
   if (len === 0) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/stringmatch_test.ml",
-            32,
-            22
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/stringmatch_test.ml",
+                  32,
+                  22
+                ]
+              }
+            });
   }
   if (s === "A") {
     return 2;
@@ -81,63 +86,68 @@ function tst02(s) {
 }
 
 if (tst02("") !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          37,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                37,
+                2
+              ]
+            }
+          });
 }
 
 if (tst02("A") !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          38,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                38,
+                2
+              ]
+            }
+          });
 }
 
 if (tst02("B") !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          39,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                39,
+                2
+              ]
+            }
+          });
 }
 
 if (tst02("\0\0\0\0\0\0\0\x07") !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          40,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                40,
+                2
+              ]
+            }
+          });
 }
 
 if (tst02("\0\0\0\x03") !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          41,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                41,
+                2
+              ]
+            }
+          });
 }
 
 function tst03(s) {
@@ -196,579 +206,627 @@ function tst03(s) {
 }
 
 if (tst03("get_const") !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          123,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                123,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("set_congt") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          124,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                124,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("get_var") !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          125,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                125,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("gat_ver") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          126,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                126,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("get_env") !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          127,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                127,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("get_env") !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          128,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                128,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("get_meth") !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          129,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                129,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("met_geth") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          130,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                130,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("set_var") !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          131,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                131,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("sev_tar") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          132,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                132,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_const") !== 5) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          133,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                133,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("ppa_const") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          134,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                134,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_var") !== 6) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          135,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                135,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_var") !== 6) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          136,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                136,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_env") !== 7) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          137,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                137,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("epp_anv") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          138,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                138,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_meth") !== 8) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          139,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                139,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("atp_meph") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          140,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                140,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_const_const") !== 9) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          141,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                141,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_const_const") !== 9) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          142,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                142,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_const_var") !== 10) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          143,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                143,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("atp_consp_var") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          144,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                144,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_const_env") !== 11) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          145,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                145,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_constne_v") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          146,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                146,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_const_meth") !== 12) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          147,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                147,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("spp_conat_meth") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          148,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                148,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_var_const") !== 13) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          149,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                149,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_va_rconst") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          150,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                150,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_env_const") !== 14) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          151,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                151,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_env_const") !== 14) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          152,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                152,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_meth_const") !== 15) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          153,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                153,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("app_teth_consm") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          154,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                154,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("meth_app_const") !== 16) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          155,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                155,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("math_epp_const") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          156,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                156,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("meth_app_var") !== 17) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          157,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                157,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("meth_app_var") !== 17) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          158,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                158,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("meth_app_env") !== 18) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          159,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                159,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("eeth_app_mnv") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          160,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                160,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("meth_app_meth") !== 19) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          161,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                161,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("meth_apt_meph") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          162,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                162,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("send_const") !== 20) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          163,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                163,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("tend_conss") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          164,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                164,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("send_var") !== 21) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          165,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                165,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("serd_van") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          166,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                166,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("send_env") !== 22) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          167,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                167,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("sen_denv") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          168,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                168,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("send_meth") !== 23) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          169,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                169,
+                2
+              ]
+            }
+          });
 }
 
 if (tst03("tend_mesh") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          170,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                170,
+                2
+              ]
+            }
+          });
 }
 
 function tst04(s) {
@@ -803,231 +861,250 @@ function tst04(s) {
 }
 
 if (tst04("AAAAAAAA") !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          204,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                204,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("AAAAAAAAAAAAAAAA") !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          205,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                205,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("AAAAAAAAAAAAAAAAAAAAAAAA") !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          206,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                206,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA") !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          207,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                207,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("BBBBBBBB") !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          208,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                208,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("BBBBBBBBBBBBBBBB") !== 5) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          209,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                209,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("BBBBBBBBBBBBBBBBBBBBBBBB") !== 6) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          210,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                210,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB") !== 7) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          211,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                211,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("CCCCCCCC") !== 8) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          212,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                212,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("CCCCCCCCCCCCCCCC") !== 9) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          213,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                213,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("CCCCCCCCCCCCCCCCCCCCCCCC") !== 10) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          214,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                214,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC") !== 11) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          215,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                215,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          216,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                216,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("DDD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          217,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                217,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("DDDDDDD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          218,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                218,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("AAADDDD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          219,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                219,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("AAAAAAADDDDDDDD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          220,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                220,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("AAAAAAADDDD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          221,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                221,
+                2
+              ]
+            }
+          });
 }
 
 if (tst04("AAAAAAAAAAAAAAADDDD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          222,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                222,
+                2
+              ]
+            }
+          });
 }
 
 function tst05(s) {
@@ -1064,267 +1141,289 @@ function tst05(s) {
 }
 
 if (tst05("AAA") !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          258,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                258,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAA") !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          259,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                259,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAAA") !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          260,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                260,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAAAA") !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          261,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                261,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAAAAA") !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          262,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                262,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAAAAAAAAAA") !== 5) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          263,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                263,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAAAAAAAAAAAAAA") !== 6) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          264,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                264,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAAAAAAAAAAAAAAAAAA") !== 7) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          265,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                265,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("BBB") !== 8) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          266,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                266,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("BBBB") !== 9) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          267,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                267,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("BBBBB") !== 10) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          268,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                268,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("BBBBBB") !== 11) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          269,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                269,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("BBBBBBB") !== 12) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          270,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                270,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          271,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                271,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          272,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                272,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          273,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                273,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAAAAD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          274,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                274,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("AAAAAAAD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          275,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                275,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("BBD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          276,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                276,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("BBBD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          277,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                277,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("BBBBBBD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          278,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                278,
+                2
+              ]
+            }
+          });
 }
 
 if (tst05("BBBBBBBD") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          279,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                279,
+                2
+              ]
+            }
+          });
 }
 
 var s00 = "and";
@@ -1887,2223 +1986,2408 @@ function tst06(s) {
 }
 
 if (tst06(s00) !== 0) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          565,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                565,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t00) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          566,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                566,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s01) !== 1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          567,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                567,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t01) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          568,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                568,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s02) !== 2) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          569,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                569,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t02) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          570,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                570,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s03) !== 3) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          571,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                571,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t03) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          572,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                572,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s04) !== 4) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          573,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                573,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t04) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          574,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                574,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s05) !== 5) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          575,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                575,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t05) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          576,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                576,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s06) !== 6) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          577,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                577,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t06) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          578,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                578,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s07) !== 7) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          579,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                579,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t07) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          580,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                580,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s08) !== 8) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          581,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                581,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t08) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          582,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                582,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s09) !== 9) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          583,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                583,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t09) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          584,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                584,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s10) !== 10) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          585,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                585,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t10) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          586,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                586,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s11) !== 11) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          587,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                587,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t11) !== 11) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          588,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                588,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s12) !== 12) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          589,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                589,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t12) !== 12) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          590,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                590,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s13) !== 13) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          591,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                591,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t13) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          592,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                592,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s14) !== 14) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          593,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                593,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t14) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          594,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                594,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s15) !== 15) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          595,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                595,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t15) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          596,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                596,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s16) !== 16) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          597,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                597,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t16) !== 16) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          598,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                598,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s17) !== 17) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          599,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                599,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t17) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          600,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                600,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s18) !== 18) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          601,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                601,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t18) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          602,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                602,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s19) !== 19) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          603,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                603,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t19) !== 19) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          604,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                604,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s20) !== 20) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          605,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                605,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t20) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          606,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                606,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s21) !== 21) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          607,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                607,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t21) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          608,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                608,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s22) !== 22) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          609,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                609,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t22) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          610,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                610,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s23) !== 23) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          611,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                611,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t23) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          612,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                612,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s24) !== 24) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          613,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                613,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t24) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          614,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                614,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s25) !== 25) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          615,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                615,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t25) !== 25) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          616,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                616,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s26) !== 26) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          617,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                617,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t26) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          618,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                618,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s27) !== 27) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          619,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                619,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t27) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          620,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                620,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s28) !== 28) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          621,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                621,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t28) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          622,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                622,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s29) !== 29) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          623,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                623,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t29) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          624,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                624,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s30) !== 30) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          625,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                625,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t30) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          626,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                626,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s31) !== 31) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          627,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                627,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t31) !== 31) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          628,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                628,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s32) !== 32) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          629,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                629,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t32) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          630,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                630,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s33) !== 33) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          631,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                631,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t33) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          632,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                632,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s34) !== 34) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          633,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                633,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t34) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          634,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                634,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s35) !== 35) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          635,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                635,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t35) !== 35) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          636,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                636,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s36) !== 36) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          637,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                637,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t36) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          638,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                638,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s37) !== 37) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          639,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                639,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t37) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          640,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                640,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s38) !== 38) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          641,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                641,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t38) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          642,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                642,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s39) !== 39) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          643,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                643,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t39) !== 39) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          644,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                644,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s40) !== 40) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          645,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                645,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t40) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          646,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                646,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s41) !== 41) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          647,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                647,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t41) !== 41) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          648,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                648,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s42) !== 42) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          649,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                649,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t42) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          650,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                650,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s43) !== 43) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          651,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                651,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t43) !== 43) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          652,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                652,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s44) !== 44) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          653,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                653,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t44) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          654,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                654,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s45) !== 45) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          655,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                655,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t45) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          656,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                656,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s46) !== 46) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          657,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                657,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t46) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          658,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                658,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s47) !== 47) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          659,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                659,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t47) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          660,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                660,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s48) !== 48) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          661,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                661,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t48) !== 48) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          662,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                662,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s49) !== 49) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          663,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                663,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t49) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          664,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                664,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s50) !== 50) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          665,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                665,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t50) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          666,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                666,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s51) !== 51) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          667,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                667,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t51) !== 51) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          668,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                668,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s52) !== 52) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          669,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                669,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t52) !== 52) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          670,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                670,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s53) !== 53) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          671,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                671,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t53) !== 53) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          672,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                672,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s54) !== 54) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          673,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                673,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t54) !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          674,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                674,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s55) !== 55) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          675,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                675,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t55) !== 55) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          676,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                676,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s56) !== 56) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          677,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                677,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t56) !== 56) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          678,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                678,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s57) !== 57) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          679,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                679,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t57) !== 57) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          680,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                680,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s58) !== 58) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          681,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                681,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t58) !== 58) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          682,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                682,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s59) !== 59) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          683,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                683,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t59) !== 59) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          684,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                684,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s60) !== 60) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          685,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                685,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t60) !== 60) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          686,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                686,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s61) !== 61) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          687,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                687,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t61) !== 61) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          688,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                688,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s62) !== 62) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          689,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                689,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t62) !== 62) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          690,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                690,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s63) !== 63) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          691,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                691,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t63) !== 63) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          692,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                692,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s64) !== 64) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          693,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                693,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t64) !== 64) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          694,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                694,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s65) !== 65) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          695,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                695,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t65) !== 65) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          696,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                696,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s66) !== 66) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          697,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                697,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t66) !== 66) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          698,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                698,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s67) !== 67) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          699,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                699,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t67) !== 67) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          700,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                700,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s68) !== 68) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          701,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                701,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t68) !== 68) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          702,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                702,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s69) !== 69) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          703,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                703,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t69) !== 69) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          704,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                704,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s70) !== 70) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          705,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                705,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t70) !== 70) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          706,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                706,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s71) !== 71) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          707,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                707,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t71) !== 71) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          708,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                708,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s72) !== 72) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          709,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                709,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t72) !== 72) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          710,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                710,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s73) !== 73) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          711,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                711,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t73) !== 73) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          712,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                712,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s74) !== 74) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          713,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                713,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t74) !== 74) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          714,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                714,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s75) !== 75) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          715,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                715,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t75) !== 75) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          716,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                716,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s76) !== 76) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          717,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                717,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t76) !== 76) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          718,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                718,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s77) !== 77) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          719,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                719,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t77) !== 77) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          720,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                720,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s78) !== 78) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          721,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                721,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t78) !== 78) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          722,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                722,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s79) !== 79) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          723,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                723,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t79) !== 79) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          724,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                724,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s80) !== 80) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          725,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                725,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t80) !== 80) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          726,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                726,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s81) !== 81) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          727,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                727,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t81) !== 81) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          728,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                728,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s82) !== 82) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          729,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                729,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t82) !== 82) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          730,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                730,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s83) !== 83) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          731,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                731,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t83) !== 83) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          732,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                732,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s84) !== 84) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          733,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                733,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t84) !== 84) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          734,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                734,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s85) !== 85) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          735,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                735,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t85) !== 85) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          736,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                736,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s86) !== 86) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          737,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                737,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t86) !== 86) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          738,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                738,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s87) !== 87) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          739,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                739,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t87) !== 87) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          740,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                740,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s88) !== 88) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          741,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                741,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t88) !== 88) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          742,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                742,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s89) !== 89) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          743,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                743,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t89) !== 89) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          744,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                744,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s90) !== 90) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          745,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                745,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t90) !== 90) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          746,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                746,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(s91) !== 91) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          747,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                747,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06(t91) !== 91) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          748,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                748,
+                2
+              ]
+            }
+          });
 }
 
 if (tst06("") !== -1) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/stringmatch_test.ml",
-          749,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/stringmatch_test.ml",
+                749,
+                2
+              ]
+            }
+          });
 }
 
 exports.tst01 = tst01;
diff --git a/jscomp/test/dist/jscomp/test/test_array_primitive.js b/jscomp/test/dist/jscomp/test/test_array_primitive.js
index b99f8a3f98..8fa84f6ad7 100644
--- a/jscomp/test/dist/jscomp/test/test_array_primitive.js
+++ b/jscomp/test/dist/jscomp/test/test_array_primitive.js
@@ -13,22 +13,24 @@ function caml_array_sub(x, offset, len) {
 
 function caml_array_set(xs, index, newval) {
   if (index < 0 || index >= xs.length) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "index out of bounds",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "index out of bounds"
+              }
+            });
   }
   Caml_array.set(xs, index, newval);
 }
 
 function caml_array_get(xs, index) {
   if (index < 0 || index >= xs.length) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "index out of bounds",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "index out of bounds"
+              }
+            });
   }
   return Caml_array.get(xs, index);
 }
diff --git a/jscomp/test/dist/jscomp/test/test_bool_equal.js b/jscomp/test/dist/jscomp/test/test_bool_equal.js
index 9339a09c12..5109459de8 100644
--- a/jscomp/test/dist/jscomp/test/test_bool_equal.js
+++ b/jscomp/test/dist/jscomp/test/test_bool_equal.js
@@ -19,50 +19,54 @@ function bool_equal(x, y) {
 
 function assertions(param) {
   if (true !== true) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_bool_equal.ml",
-            25,
-            2
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_bool_equal.ml",
+                  25,
+                  2
+                ]
+              }
+            });
   }
   if (false !== false) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_bool_equal.ml",
-            26,
-            2
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_bool_equal.ml",
+                  26,
+                  2
+                ]
+              }
+            });
   }
   if (true === false) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_bool_equal.ml",
-            27,
-            2
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_bool_equal.ml",
+                  27,
+                  2
+                ]
+              }
+            });
   }
   if (false !== true) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/test_bool_equal.ml",
-          28,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/test_bool_equal.ml",
+                28,
+                2
+              ]
+            }
+          });
 }
 
 function f0(x) {
diff --git a/jscomp/test/dist/jscomp/test/test_closure.js b/jscomp/test/dist/jscomp/test/test_closure.js
index e23268002d..63b726f89b 100644
--- a/jscomp/test/dist/jscomp/test/test_closure.js
+++ b/jscomp/test/dist/jscomp/test/test_closure.js
@@ -30,15 +30,16 @@ Stdlib__Array.iter((function (x) {
       }), u);
 
 if (v.contents !== 45) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/test_closure.ml",
-          53,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/test_closure.ml",
+                53,
+                2
+              ]
+            }
+          });
 }
 
 exports.v = v;
diff --git a/jscomp/test/dist/jscomp/test/test_exception.js b/jscomp/test/dist/jscomp/test/test_exception.js
index 2afd20fa27..fa701db18c 100644
--- a/jscomp/test/dist/jscomp/test/test_exception.js
+++ b/jscomp/test/dist/jscomp/test/test_exception.js
@@ -8,41 +8,46 @@ var Test_common = require("./test_common.js");
 var Local = /* @__PURE__ */Caml_exceptions.create("Test_exception.Local");
 
 function f(param) {
-  throw {
-        MEL_EXN_ID: Local,
-        _1: 3,
-        Error: new Error()
-      };
+  throw new Error(Local, {
+            cause: {
+              MEL_EXN_ID: Local,
+              _1: 3
+            }
+          });
 }
 
 function g(param) {
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function h(param) {
-  throw {
-        MEL_EXN_ID: Test_common.U,
-        _1: 3,
-        Error: new Error()
-      };
+  throw new Error(Test_common.U, {
+            cause: {
+              MEL_EXN_ID: Test_common.U,
+              _1: 3
+            }
+          });
 }
 
 function x(param) {
-  throw {
-        MEL_EXN_ID: Test_common.H,
-        Error: new Error()
-      };
+  throw new Error(Test_common.H, {
+            cause: {
+              MEL_EXN_ID: Test_common.H
+            }
+          });
 }
 
 function xx(param) {
-  throw {
-        MEL_EXN_ID: Stdlib.Invalid_argument,
-        _1: "x",
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Invalid_argument, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Invalid_argument,
+              _1: "x"
+            }
+          });
 }
 
 var Nullary = /* @__PURE__ */Caml_exceptions.create("Test_exception.Nullary");
diff --git a/jscomp/test/dist/jscomp/test/test_exception_escape.js b/jscomp/test/dist/jscomp/test/test_exception_escape.js
index 57a49d4d4f..9ec824165e 100644
--- a/jscomp/test/dist/jscomp/test/test_exception_escape.js
+++ b/jscomp/test/dist/jscomp/test/test_exception_escape.js
@@ -8,11 +8,12 @@ var A = /* @__PURE__ */Caml_exceptions.create("Test_exception_escape.N.A");
 var f;
 
 try {
-  throw {
-        MEL_EXN_ID: A,
-        _1: 3,
-        Error: new Error()
-      };
+  throw new Error(A, {
+            cause: {
+              MEL_EXN_ID: A,
+              _1: 3
+            }
+          });
 }
 catch (exn){
   f = 3;
diff --git a/jscomp/test/dist/jscomp/test/test_for_map.js b/jscomp/test/dist/jscomp/test/test_for_map.js
index 71a5fdd704..12a203b9fb 100644
--- a/jscomp/test/dist/jscomp/test/test_for_map.js
+++ b/jscomp/test/dist/jscomp/test/test_for_map.js
@@ -59,17 +59,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -91,17 +93,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function is_empty(param) {
@@ -167,10 +171,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -207,10 +212,11 @@ function find_first(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -284,10 +290,11 @@ function find_last(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -372,10 +379,11 @@ function min_binding(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -410,10 +418,11 @@ function max_binding(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -443,11 +452,12 @@ function remove_min_binding(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.remove_min_elt"
+            }
+          });
 }
 
 function merge(t1, t2) {
@@ -758,15 +768,16 @@ function merge$1(f, s1, s2) {
     var match$1 = split(v2, s1);
     return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/stdlib/map.ml",
-          408,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/stdlib/map.ml",
+                408,
+                10
+              ]
+            }
+          });
 }
 
 function union(f, s1, s2) {
diff --git a/jscomp/test/dist/jscomp/test/test_incomplete.js b/jscomp/test/dist/jscomp/test/test_incomplete.js
index dff907b33b..78e0bdf73a 100644
--- a/jscomp/test/dist/jscomp/test/test_incomplete.js
+++ b/jscomp/test/dist/jscomp/test/test_incomplete.js
@@ -6,15 +6,16 @@ function f(x) {
   if (!(x > 3 || x < 1)) {
     return /* 'a' */97;
   }
-  throw {
-        MEL_EXN_ID: "Match_failure",
-        _1: [
-          "test_incomplete.ml",
-          3,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Match_failure", {
+            cause: {
+              MEL_EXN_ID: "Match_failure",
+              _1: [
+                "test_incomplete.ml",
+                3,
+                2
+              ]
+            }
+          });
 }
 
 function f2(x) {
diff --git a/jscomp/test/dist/jscomp/test/test_int_map_find.js b/jscomp/test/dist/jscomp/test/test_int_map_find.js
index ab9a603dff..3b1e89611c 100644
--- a/jscomp/test/dist/jscomp/test/test_int_map_find.js
+++ b/jscomp/test/dist/jscomp/test/test_int_map_find.js
@@ -46,17 +46,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -78,17 +80,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add(x, data, m) {
diff --git a/jscomp/test/dist/jscomp/test/test_internalOO.js b/jscomp/test/dist/jscomp/test/test_internalOO.js
index 8579dbf5b0..f70d997b83 100644
--- a/jscomp/test/dist/jscomp/test/test_internalOO.js
+++ b/jscomp/test/dist/jscomp/test/test_internalOO.js
@@ -94,17 +94,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -126,17 +128,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function is_empty(param) {
@@ -202,10 +206,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -242,10 +247,11 @@ function find_first(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -319,10 +325,11 @@ function find_last(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -407,10 +414,11 @@ function min_binding(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -445,10 +453,11 @@ function max_binding(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -478,11 +487,12 @@ function remove_min_binding(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.remove_min_elt"
+            }
+          });
 }
 
 function merge(t1, t2) {
@@ -793,15 +803,16 @@ function merge$1(f, s1, s2) {
     var match$1 = split(v2, s1);
     return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/stdlib/map.ml",
-          408,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/stdlib/map.ml",
+                408,
+                10
+              ]
+            }
+          });
 }
 
 function union(f, s1, s2) {
@@ -1227,17 +1238,19 @@ function bal$1(l, x, d, r) {
       if (lr) {
         return create$1(create$1(ll, lv, ld, lr.l), lr.v, lr.d, create$1(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -1259,17 +1272,19 @@ function bal$1(l, x, d, r) {
     if (rl) {
       return create$1(create$1(l, x, d, rl.l), rl.v, rl.d, create$1(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function is_empty$1(param) {
@@ -1335,10 +1350,11 @@ function find$1(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1375,10 +1391,11 @@ function find_first$1(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1452,10 +1469,11 @@ function find_last$1(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1540,10 +1558,11 @@ function min_binding$1(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1578,10 +1597,11 @@ function max_binding$1(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1611,11 +1631,12 @@ function remove_min_binding$1(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.remove_min_elt"
+            }
+          });
 }
 
 function merge$2(t1, t2) {
@@ -1926,15 +1947,16 @@ function merge$3(f, s1, s2) {
     var match$1 = split$1(v2, s1);
     return concat_or_join$1(merge$3(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$3(f, match$1[2], s2.r));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/stdlib/map.ml",
-          408,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/stdlib/map.ml",
+                408,
+                10
+              ]
+            }
+          });
 }
 
 function union$1(f, s1, s2) {
@@ -2360,17 +2382,19 @@ function bal$2(l, x, d, r) {
       if (lr) {
         return create$2(create$2(ll, lv, ld, lr.l), lr.v, lr.d, create$2(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -2392,17 +2416,19 @@ function bal$2(l, x, d, r) {
     if (rl) {
       return create$2(create$2(l, x, d, rl.l), rl.v, rl.d, create$2(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function is_empty$2(param) {
@@ -2468,10 +2494,11 @@ function find$2(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -2508,10 +2535,11 @@ function find_first$2(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -2585,10 +2613,11 @@ function find_last$2(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -2673,10 +2702,11 @@ function min_binding$2(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -2711,10 +2741,11 @@ function max_binding$2(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -2744,11 +2775,12 @@ function remove_min_binding$2(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.remove_min_elt"
+            }
+          });
 }
 
 function merge$4(t1, t2) {
@@ -3059,15 +3091,16 @@ function merge$5(f, s1, s2) {
     var match$1 = split$2(v2, s1);
     return concat_or_join$2(merge$5(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$5(f, match$1[2], s2.r));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/stdlib/map.ml",
-          408,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/stdlib/map.ml",
+                408,
+                10
+              ]
+            }
+          });
 }
 
 function union$2(f, s1, s2) {
@@ -3527,7 +3560,9 @@ function get_method_label(table, name) {
       table.methods_by_label = Curry._3(add$2, label, true, table.methods_by_label);
       return label;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -3562,7 +3597,9 @@ function get_method(table, label) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return Caml_array.get(table.methods, label);
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -3619,7 +3656,9 @@ function narrow(table, vars, virt_meths, concr_meths) {
             if (exn.MEL_EXN_ID === Stdlib.Not_found) {
               tmp = true;
             } else {
-              throw exn;
+              throw new Error(exn.MEL_EXN_ID, {
+                        cause: exn
+                      });
             }
           }
           by_label.contents = Curry._3(add$2, label, tmp, by_label.contents);
@@ -3682,7 +3721,9 @@ function new_variable(table, name) {
       }
       return index;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -3715,17 +3756,20 @@ function get_variable(table, name) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/test_internalOO.ml",
-              280,
-              50
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/test_internalOO.ml",
+                    280,
+                    50
+                  ]
+                }
+              });
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -3805,11 +3849,12 @@ function make_class_store(pub_meths, class_init, init_table) {
 
 function dummy_class(loc) {
   var undef = function (param) {
-    throw {
-          MEL_EXN_ID: Stdlib.Undefined_recursive_module,
-          _1: loc,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Undefined_recursive_module, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Undefined_recursive_module,
+                _1: loc
+              }
+            });
   };
   return [
           undef,
diff --git a/jscomp/test/dist/jscomp/test/test_list.js b/jscomp/test/dist/jscomp/test/test_list.js
index a63038bb38..e33ae0bed7 100644
--- a/jscomp/test/dist/jscomp/test/test_list.js
+++ b/jscomp/test/dist/jscomp/test/test_list.js
@@ -27,31 +27,34 @@ function hd(param) {
   if (param) {
     return param.hd;
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "hd",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "hd"
+            }
+          });
 }
 
 function tl(param) {
   if (param) {
     return param.tl;
   }
-  throw {
-        MEL_EXN_ID: "Failure",
-        _1: "tl",
-        Error: new Error()
-      };
+  throw new Error("Failure", {
+            cause: {
+              MEL_EXN_ID: "Failure",
+              _1: "tl"
+            }
+          });
 }
 
 function nth(l, n) {
   if (n < 0) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.nth",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.nth"
+              }
+            });
   }
   var _l = l;
   var _n = n;
@@ -66,11 +69,12 @@ function nth(l, n) {
       _l = l$1.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "nth",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "nth"
+              }
+            });
   };
 }
 
@@ -204,20 +208,22 @@ function map2(f, l1, l2) {
               tl: map2(f, l1.tl, l2.tl)
             };
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.map2",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.map2"
+              }
+            });
   }
   if (!l2) {
     return /* [] */0;
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "List.map2",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "List.map2"
+            }
+          });
 }
 
 function rev_map2(f, l1, l2) {
@@ -238,18 +244,20 @@ function rev_map2(f, l1, l2) {
         };
         continue ;
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "List.rev_map2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "List.rev_map2"
+                }
+              });
     }
     if (l2$1) {
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "List.rev_map2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "List.rev_map2"
+                }
+              });
     }
     return accu;
   };
@@ -266,20 +274,22 @@ function iter2(f, _l1, _l2) {
         _l1 = l1.tl;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "List.iter2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "List.iter2"
+                }
+              });
     }
     if (!l2) {
       return ;
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.iter2",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.iter2"
+              }
+            });
   };
 }
 
@@ -295,18 +305,20 @@ function fold_left2(f, _accu, _l1, _l2) {
         _accu = Curry._3(f, accu, l1.hd, l2.hd);
         continue ;
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "List.fold_left2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "List.fold_left2"
+                }
+              });
     }
     if (l2) {
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "List.fold_left2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "List.fold_left2"
+                }
+              });
     }
     return accu;
   };
@@ -317,18 +329,20 @@ function fold_right2(f, l1, l2, accu) {
     if (l2) {
       return Curry._3(f, l1.hd, l2.hd, fold_right2(f, l1.tl, l2.tl, accu));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.fold_right2"
+              }
+            });
   }
   if (l2) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.fold_right2",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.fold_right2"
+              }
+            });
   }
   return accu;
 }
@@ -374,20 +388,22 @@ function for_all2(p, _l1, _l2) {
         _l1 = l1.tl;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "List.for_all2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "List.for_all2"
+                }
+              });
     }
     if (!l2) {
       return true;
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.for_all2",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.for_all2"
+              }
+            });
   };
 }
 
@@ -404,20 +420,22 @@ function exists2(p, _l1, _l2) {
         _l1 = l1.tl;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "List.exists2",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "List.exists2"
+                }
+              });
     }
     if (!l2) {
       return false;
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.exists2",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.exists2"
+              }
+            });
   };
 }
 
@@ -460,10 +478,11 @@ function assoc(x, _param) {
       _param = param.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -478,10 +497,11 @@ function assq(x, _param) {
       _param = param.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -556,10 +576,11 @@ function find(p, _param) {
       _param = param.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -654,20 +675,22 @@ function combine(l1, l2) {
               tl: combine(l1.tl, l2.tl)
             };
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "List.combine",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "List.combine"
+              }
+            });
   }
   if (!l2) {
     return /* [] */0;
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "List.combine",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "List.combine"
+            }
+          });
 }
 
 function merge(cmp, l1, l2) {
@@ -704,15 +727,16 @@ function chop(_k, _l) {
       _k = k - 1 | 0;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_list.ml",
-            224,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_list.ml",
+                  224,
+                  11
+                ]
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/test_match_exception.js b/jscomp/test/dist/jscomp/test/test_match_exception.js
index 3dbe373011..f67774141c 100644
--- a/jscomp/test/dist/jscomp/test/test_match_exception.js
+++ b/jscomp/test/dist/jscomp/test/test_match_exception.js
@@ -14,7 +14,9 @@ function f(g, x) {
     if (exn.MEL_EXN_ID === Stdlib.Not_found) {
       return 3;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/test_per.js b/jscomp/test/dist/jscomp/test/test_per.js
index 785b03627f..33cff5a097 100644
--- a/jscomp/test/dist/jscomp/test/test_per.js
+++ b/jscomp/test/dist/jscomp/test/test_per.js
@@ -15,19 +15,21 @@ var Curry = require("melange.js/curry.js");
 var Stdlib = require("melange/stdlib.js");
 
 function failwith(s) {
-  throw {
-        MEL_EXN_ID: Stdlib.Failure,
-        _1: s,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Failure, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Failure,
+              _1: s
+            }
+          });
 }
 
 function invalid_arg(s) {
-  throw {
-        MEL_EXN_ID: Stdlib.Invalid_argument,
-        _1: s,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Invalid_argument, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Invalid_argument,
+              _1: s
+            }
+          });
 }
 
 var Exit = /* @__PURE__ */Caml_exceptions.create("Test_per.Exit");
@@ -103,11 +105,12 @@ function $caret(s1, s2) {
 
 function char_of_int(n) {
   if (n < 0 || n > 255) {
-    throw {
-          MEL_EXN_ID: Stdlib.Invalid_argument,
-          _1: "char_of_int",
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Invalid_argument, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Invalid_argument,
+                _1: "char_of_int"
+              }
+            });
   }
   return n;
 }
@@ -127,11 +130,12 @@ function bool_of_string(param) {
     case "true" :
         return true;
     default:
-      throw {
-            MEL_EXN_ID: Stdlib.Invalid_argument,
-            _1: "bool_of_string",
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Invalid_argument, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Invalid_argument,
+                  _1: "bool_of_string"
+                }
+              });
   }
 }
 
@@ -248,22 +252,24 @@ function output_string(oc, s) {
 
 function output(oc, s, ofs, len) {
   if (ofs < 0 || len < 0 || ofs > (s.length - len | 0)) {
-    throw {
-          MEL_EXN_ID: Stdlib.Invalid_argument,
-          _1: "output",
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Invalid_argument, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Invalid_argument,
+                _1: "output"
+              }
+            });
   }
   Caml_io.caml_ml_output(oc, s, ofs, len);
 }
 
 function output_substring(oc, s, ofs, len) {
   if (ofs < 0 || len < 0 || ofs > (s.length - len | 0)) {
-    throw {
-          MEL_EXN_ID: Stdlib.Invalid_argument,
-          _1: "output_substring",
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Invalid_argument, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Invalid_argument,
+                _1: "output_substring"
+              }
+            });
   }
   Caml_io.caml_ml_output(oc, s, ofs, len);
 }
@@ -318,11 +324,12 @@ function open_in_bin(name) {
 
 function input(ic, s, ofs, len) {
   if (ofs < 0 || len < 0 || ofs > (s.length - len | 0)) {
-    throw {
-          MEL_EXN_ID: Stdlib.Invalid_argument,
-          _1: "input",
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Invalid_argument, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Invalid_argument,
+                _1: "input"
+              }
+            });
   }
   return Caml_external_polyfill.resolve("caml_ml_input")(ic, s, ofs, len);
 }
@@ -336,10 +343,11 @@ function unsafe_really_input(ic, s, _ofs, _len) {
     }
     var r = Caml_external_polyfill.resolve("caml_ml_input")(ic, s, ofs, len);
     if (r === 0) {
-      throw {
-            MEL_EXN_ID: Stdlib.End_of_file,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.End_of_file, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.End_of_file
+                }
+              });
     }
     _len = len - r | 0;
     _ofs = ofs + r | 0;
@@ -349,11 +357,12 @@ function unsafe_really_input(ic, s, _ofs, _len) {
 
 function really_input(ic, s, ofs, len) {
   if (ofs < 0 || len < 0 || ofs > (s.length - len | 0)) {
-    throw {
-          MEL_EXN_ID: Stdlib.Invalid_argument,
-          _1: "really_input",
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Invalid_argument, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Invalid_argument,
+                _1: "really_input"
+              }
+            });
   }
   unsafe_really_input(ic, s, ofs, len);
 }
@@ -390,10 +399,11 @@ function input_line(chan) {
       if (accu) {
         return build_result(Caml_bytes.caml_create_bytes(len), len, accu);
       }
-      throw {
-            MEL_EXN_ID: Stdlib.End_of_file,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.End_of_file, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.End_of_file
+                }
+              });
     }
     if (n > 0) {
       var res = Caml_bytes.caml_create_bytes(n - 1 | 0);
diff --git a/jscomp/test/dist/jscomp/test/test_seq.js b/jscomp/test/dist/jscomp/test/test_seq.js
index 307c8b7a6b..2beacfadc2 100644
--- a/jscomp/test/dist/jscomp/test/test_seq.js
+++ b/jscomp/test/dist/jscomp/test/test_seq.js
@@ -24,22 +24,24 @@ function assoc3(x, _l) {
       _l = l.tl;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
 function help_action(param) {
-  throw {
-        MEL_EXN_ID: Stop,
-        _1: {
-          TAG: /* Unknown */0,
-          _0: "-help"
-        },
-        Error: new Error()
-      };
+  throw new Error(Stop, {
+            cause: {
+              MEL_EXN_ID: Stop,
+              _1: {
+                TAG: /* Unknown */0,
+                _0: "-help"
+              }
+            }
+          });
 }
 
 function v(speclist) {
@@ -72,7 +74,9 @@ function add_help(speclist) {
         tl: /* [] */0
       };
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
   var add2;
@@ -95,7 +99,9 @@ function add_help(speclist) {
         tl: /* [] */0
       };
     } else {
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
   }
   return Stdlib.$at(speclist, Stdlib.$at(add1, add2));
diff --git a/jscomp/test/dist/jscomp/test/test_set.js b/jscomp/test/dist/jscomp/test/test_set.js
index 7914c9a38f..8dd176fa99 100644
--- a/jscomp/test/dist/jscomp/test/test_set.js
+++ b/jscomp/test/dist/jscomp/test/test_set.js
@@ -37,17 +37,19 @@ function Make(Ord) {
         if (lr) {
           return create(create(ll, lv, lr._0), lr._1, create(lr._2, v, r));
         }
-        throw {
-              MEL_EXN_ID: "Invalid_argument",
-              _1: "Set.bal",
-              Error: new Error()
-            };
-      }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+        throw new Error("Invalid_argument", {
+                  cause: {
+                    MEL_EXN_ID: "Invalid_argument",
+                    _1: "Set.bal"
+                  }
+                });
+      }
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
     if (hr <= (hl + 2 | 0)) {
       return /* Node */{
@@ -67,17 +69,19 @@ function Make(Ord) {
       if (rl) {
         return create(create(l, v, rl._0), rl._1, create(rl._2, rv, rr));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   };
   var add = function (x, t) {
     if (!t) {
@@ -150,10 +154,11 @@ function Make(Ord) {
         _param = l;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     };
   };
   var max_elt = function (_param) {
@@ -166,10 +171,11 @@ function Make(Ord) {
         _param = param._2;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     };
   };
   var remove_min_elt = function (param) {
@@ -181,11 +187,12 @@ function Make(Ord) {
         return param._2;
       }
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.remove_min_elt",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.remove_min_elt"
+              }
+            });
   };
   var merge = function (t1, t2) {
     if (t1) {
@@ -567,10 +574,11 @@ function Make(Ord) {
         _param = c < 0 ? param._0 : param._2;
         continue ;
       }
-      throw {
-            MEL_EXN_ID: Stdlib.Not_found,
-            Error: new Error()
-          };
+      throw new Error(Stdlib.Not_found, {
+                cause: {
+                  MEL_EXN_ID: Stdlib.Not_found
+                }
+              });
     };
   };
   var of_sorted_list = function (l) {
@@ -660,15 +668,16 @@ function Make(Ord) {
                 match$4[1]
               ];
       }
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/test_set.ml",
-              372,
-              18
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/test_set.ml",
+                    372,
+                    18
+                  ]
+                }
+              });
     };
     return sub(Stdlib__List.length(l), l)[0];
   };
diff --git a/jscomp/test/dist/jscomp/test/test_simple_obj.js b/jscomp/test/dist/jscomp/test/test_simple_obj.js
index 0ccccedb3c..52cea27a6b 100644
--- a/jscomp/test/dist/jscomp/test/test_simple_obj.js
+++ b/jscomp/test/dist/jscomp/test/test_simple_obj.js
@@ -89,83 +89,90 @@ var v = CamlinternalOO.create_object_opt(undefined, $$class$3);
 
 function test(param) {
   if (Caml_oo_curry.js1(23515, 1, uu) !== "uu") {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_simple_obj.ml",
-            21,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_simple_obj.ml",
+                  21,
+                  4
+                ]
+              }
+            });
   }
   if (Caml_oo_curry.js3(4846113, 2, uuu, 1, 20) !== 21) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_simple_obj.ml",
-            22,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_simple_obj.ml",
+                  22,
+                  4
+                ]
+              }
+            });
   }
   if (Caml_oo_curry.js3(4846113, 3, v, 3, 7) !== 10) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_simple_obj.ml",
-            23,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_simple_obj.ml",
+                  23,
+                  4
+                ]
+              }
+            });
   }
   if (Caml_oo_curry.js1(5243894, 4, u) !== 3) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_simple_obj.ml",
-            25,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_simple_obj.ml",
+                  25,
+                  4
+                ]
+              }
+            });
   }
   if (Caml_oo_curry.js1(5243895, 5, u) !== 4) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_simple_obj.ml",
-            26,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_simple_obj.ml",
+                  26,
+                  4
+                ]
+              }
+            });
   }
   if (Caml_oo_curry.js3(23297, 6, u, 1, 2) !== 3) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/test_simple_obj.ml",
-            27,
-            4
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/test_simple_obj.ml",
+                  27,
+                  4
+                ]
+              }
+            });
   }
   if (Caml_oo_curry.js2(616641298, 7, u, 32) === 32) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/test_simple_obj.ml",
-          28,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/test_simple_obj.ml",
+                28,
+                4
+              ]
+            }
+          });
 }
 
 exports.u = u;
diff --git a/jscomp/test/dist/jscomp/test/test_static_catch_ident.js b/jscomp/test/dist/jscomp/test/test_static_catch_ident.js
index 6f9e23ba93..99b65ee420 100644
--- a/jscomp/test/dist/jscomp/test/test_static_catch_ident.js
+++ b/jscomp/test/dist/jscomp/test/test_static_catch_ident.js
@@ -11,7 +11,9 @@ function scanf_bad_input(ib, x) {
   if (x.MEL_EXN_ID === Scan_failure || x.MEL_EXN_ID === Stdlib.Failure) {
     s = x._1;
   } else {
-    throw x;
+    throw new Error(x.MEL_EXN_ID, {
+              cause: x
+            });
   }
   for(var _i = 0; _i <= 100; ++_i){
     console.log(s);
diff --git a/jscomp/test/dist/jscomp/test/test_string.js b/jscomp/test/dist/jscomp/test/test_string.js
index b9f24ff6bd..b09f4cdda0 100644
--- a/jscomp/test/dist/jscomp/test/test_string.js
+++ b/jscomp/test/dist/jscomp/test/test_string.js
@@ -11,15 +11,16 @@ function f(param) {
     case "bbbb" :
         return 1;
     default:
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/test_string.ml",
-              4,
-              18
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/test_string.ml",
+                    4,
+                    18
+                  ]
+                }
+              });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/test_string_case.js b/jscomp/test/dist/jscomp/test/test_string_case.js
index 7a9f74be25..8306f9b227 100644
--- a/jscomp/test/dist/jscomp/test/test_string_case.js
+++ b/jscomp/test/dist/jscomp/test/test_string_case.js
@@ -9,15 +9,16 @@ function f(param) {
     case "bcde" :
         return 1;
     default:
-      throw {
-            MEL_EXN_ID: "Assert_failure",
-            _1: [
-              "jscomp/test/test_string_case.ml",
-              4,
-              9
-            ],
-            Error: new Error()
-          };
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "jscomp/test/test_string_case.ml",
+                    4,
+                    9
+                  ]
+                }
+              });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/test_string_const.js b/jscomp/test/dist/jscomp/test/test_string_const.js
index 264c6278ba..95b5d2e6f4 100644
--- a/jscomp/test/dist/jscomp/test/test_string_const.js
+++ b/jscomp/test/dist/jscomp/test/test_string_const.js
@@ -16,7 +16,9 @@ catch (raw_exn){
     console.log(exn._1);
     hh = /* 'a' */97;
   } else {
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/test_string_map.js b/jscomp/test/dist/jscomp/test/test_string_map.js
index ab2c4b9796..d85fc6b8a8 100644
--- a/jscomp/test/dist/jscomp/test/test_string_map.js
+++ b/jscomp/test/dist/jscomp/test/test_string_map.js
@@ -46,17 +46,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -78,17 +80,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function add(x, data, m) {
@@ -146,10 +150,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
diff --git a/jscomp/test/dist/jscomp/test/test_trywith.js b/jscomp/test/dist/jscomp/test/test_trywith.js
index 2793067fec..c002f2add5 100644
--- a/jscomp/test/dist/jscomp/test/test_trywith.js
+++ b/jscomp/test/dist/jscomp/test/test_trywith.js
@@ -12,7 +12,9 @@ function ff(g, x) {
   catch (raw_exn){
     var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
     if (exn.MEL_EXN_ID !== Stdlib.Not_found) {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
     
   }
@@ -22,7 +24,9 @@ function ff(g, x) {
   catch (raw_exn$1){
     var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
     if (exn$1.MEL_EXN_ID !== Stdlib.Out_of_memory) {
-      throw exn$1;
+      throw new Error(exn$1.MEL_EXN_ID, {
+                cause: exn$1
+              });
     }
     
   }
@@ -32,7 +36,9 @@ function ff(g, x) {
   catch (raw_exn$2){
     var exn$2 = Caml_js_exceptions.internalToOCamlException(raw_exn$2);
     if (exn$2.MEL_EXN_ID !== Stdlib.Sys_error) {
-      throw exn$2;
+      throw new Error(exn$2.MEL_EXN_ID, {
+                cause: exn$2
+              });
     }
     
   }
@@ -42,7 +48,9 @@ function ff(g, x) {
   catch (raw_exn$3){
     var exn$3 = Caml_js_exceptions.internalToOCamlException(raw_exn$3);
     if (exn$3.MEL_EXN_ID !== Stdlib.Invalid_argument) {
-      throw exn$3;
+      throw new Error(exn$3.MEL_EXN_ID, {
+                cause: exn$3
+              });
     }
     
   }
@@ -52,7 +60,9 @@ function ff(g, x) {
   catch (raw_exn$4){
     var exn$4 = Caml_js_exceptions.internalToOCamlException(raw_exn$4);
     if (exn$4.MEL_EXN_ID !== Stdlib.End_of_file) {
-      throw exn$4;
+      throw new Error(exn$4.MEL_EXN_ID, {
+                cause: exn$4
+              });
     }
     
   }
@@ -62,7 +72,9 @@ function ff(g, x) {
   catch (raw_exn$5){
     var exn$5 = Caml_js_exceptions.internalToOCamlException(raw_exn$5);
     if (exn$5.MEL_EXN_ID !== Stdlib.Match_failure) {
-      throw exn$5;
+      throw new Error(exn$5.MEL_EXN_ID, {
+                cause: exn$5
+              });
     }
     
   }
@@ -72,7 +84,9 @@ function ff(g, x) {
   catch (raw_exn$6){
     var exn$6 = Caml_js_exceptions.internalToOCamlException(raw_exn$6);
     if (exn$6.MEL_EXN_ID !== Stdlib.Stack_overflow) {
-      throw exn$6;
+      throw new Error(exn$6.MEL_EXN_ID, {
+                cause: exn$6
+              });
     }
     
   }
@@ -82,7 +96,9 @@ function ff(g, x) {
   catch (raw_exn$7){
     var exn$7 = Caml_js_exceptions.internalToOCamlException(raw_exn$7);
     if (exn$7.MEL_EXN_ID !== Stdlib.Sys_blocked_io) {
-      throw exn$7;
+      throw new Error(exn$7.MEL_EXN_ID, {
+                cause: exn$7
+              });
     }
     
   }
@@ -92,7 +108,9 @@ function ff(g, x) {
   catch (raw_exn$8){
     var exn$8 = Caml_js_exceptions.internalToOCamlException(raw_exn$8);
     if (exn$8.MEL_EXN_ID !== Stdlib.Assert_failure) {
-      throw exn$8;
+      throw new Error(exn$8.MEL_EXN_ID, {
+                cause: exn$8
+              });
     }
     
   }
@@ -104,15 +122,18 @@ function ff(g, x) {
     if (exn$9.MEL_EXN_ID === Stdlib.Undefined_recursive_module) {
       return ;
     }
-    throw exn$9;
+    throw new Error(exn$9.MEL_EXN_ID, {
+              cause: exn$9
+            });
   }
 }
 
 function u(param) {
-  throw {
-        MEL_EXN_ID: Stdlib.Not_found,
-        Error: new Error()
-      };
+  throw new Error(Stdlib.Not_found, {
+            cause: {
+              MEL_EXN_ID: Stdlib.Not_found
+            }
+          });
 }
 
 function f(x) {
@@ -122,15 +143,16 @@ function f(x) {
   if (x.TAG === /* D */0) {
     return 1;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/test_trywith.ml",
-          51,
-          9
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/test_trywith.ml",
+                51,
+                9
+              ]
+            }
+          });
 }
 
 var u1 = "bad character decimal encoding \\";
diff --git a/jscomp/test/dist/jscomp/test/test_unsupported_primitive.js b/jscomp/test/dist/jscomp/test/test_unsupported_primitive.js
index 7a0a3e6f2e..850bacbf17 100644
--- a/jscomp/test/dist/jscomp/test/test_unsupported_primitive.js
+++ b/jscomp/test/dist/jscomp/test/test_unsupported_primitive.js
@@ -5,11 +5,12 @@ var Caml_external_polyfill = require("melange.js/caml_external_polyfill.js");
 
 function to_buffer(buff, ofs, len, v, flags) {
   if (ofs < 0 || len < 0 || ofs > (buff.length - len | 0)) {
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Marshal.to_buffer: substring out of bounds",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Marshal.to_buffer: substring out of bounds"
+              }
+            });
   }
   return Caml_external_polyfill.resolve("caml_output_value_to_buffer")(buff, ofs, len, v, flags);
 }
diff --git a/jscomp/test/dist/jscomp/test/test_while_closure.js b/jscomp/test/dist/jscomp/test/test_while_closure.js
index c31993cbd1..cb6b3751e7 100644
--- a/jscomp/test/dist/jscomp/test/test_while_closure.js
+++ b/jscomp/test/dist/jscomp/test/test_while_closure.js
@@ -35,15 +35,16 @@ Stdlib__Array.iter((function (x) {
 console.log(String(v.contents));
 
 if (v.contents !== 45) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/test_while_closure.ml",
-          63,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/test_while_closure.ml",
+                63,
+                4
+              ]
+            }
+          });
 }
 
 var count = 10;
diff --git a/jscomp/test/dist/jscomp/test/ticker.js b/jscomp/test/dist/jscomp/test/ticker.js
index 55bfaada94..4a08d5cd81 100644
--- a/jscomp/test/dist/jscomp/test/ticker.js
+++ b/jscomp/test/dist/jscomp/test/ticker.js
@@ -36,7 +36,9 @@ function split(delim, s) {
                   tl: l
                 };
         }
-        throw exn;
+        throw new Error(exn.MEL_EXN_ID, {
+                  cause: exn
+                });
       }
       var l_0 = Stdlib__String.sub(s, i$p + 1 | 0, (i - i$p | 0) - 1 | 0);
       var l$1 = {
@@ -165,17 +167,19 @@ function bal(l, x, d, r) {
       if (lr) {
         return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Map.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Map.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -197,17 +201,19 @@ function bal(l, x, d, r) {
     if (rl) {
       return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Map.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Map.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.bal"
+            }
+          });
 }
 
 function is_empty(param) {
@@ -273,10 +279,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -313,10 +320,11 @@ function find_first(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -390,10 +398,11 @@ function find_last(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -478,10 +487,11 @@ function min_binding(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -516,10 +526,11 @@ function max_binding(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -549,11 +560,12 @@ function remove_min_binding(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Map.remove_min_elt"
+            }
+          });
 }
 
 function merge(t1, t2) {
@@ -864,15 +876,16 @@ function merge$1(f, s1, s2) {
     var match$1 = split$1(v2, s1);
     return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/stdlib/map.ml",
-          408,
-          10
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/stdlib/map.ml",
+                408,
+                10
+              ]
+            }
+          });
 }
 
 function union(f, s1, s2) {
@@ -1315,19 +1328,21 @@ function compute_update_sequences(all_tickers) {
                 var l$1 = Stdlib__List.sort_uniq((function (lhs, rhs) {
                         var x = lhs.rank;
                         if (typeof x === "number") {
-                          throw {
-                                MEL_EXN_ID: "Failure",
-                                _1: "All nodes should be ranked",
-                                Error: new Error()
-                              };
+                          throw new Error("Failure", {
+                                    cause: {
+                                      MEL_EXN_ID: "Failure",
+                                      _1: "All nodes should be ranked"
+                                    }
+                                  });
                         }
                         var y = rhs.rank;
                         if (typeof y === "number") {
-                          throw {
-                                MEL_EXN_ID: "Failure",
-                                _1: "All nodes should be ranked",
-                                Error: new Error()
-                              };
+                          throw new Error("Failure", {
+                                    cause: {
+                                      MEL_EXN_ID: "Failure",
+                                      _1: "All nodes should be ranked"
+                                    }
+                                  });
                         }
                         return Caml.caml_int_compare(x._0, y._0);
                       }), l);
@@ -1353,11 +1368,12 @@ function process_quote(ticker_map, new_ticker, new_value) {
             ticker.value = new_value;
             return ;
           }
-          throw {
-                MEL_EXN_ID: "Failure",
-                _1: "Only single Market ticker should be udpated upon a new quote",
-                Error: new Error()
-              };
+          throw new Error("Failure", {
+                    cause: {
+                      MEL_EXN_ID: "Failure",
+                      _1: "Only single Market ticker should be udpated upon a new quote"
+                    }
+                  });
         }), update_sequence);
 }
 
@@ -1387,11 +1403,12 @@ function process_input_line(ticker_map, all_tickers, line) {
             var match$1 = match.tl;
             if (match$1) {
               if (match$1.tl) {
-                throw {
-                      MEL_EXN_ID: "Failure",
-                      _1: "Invalid input line",
-                      Error: new Error()
-                    };
+                throw new Error("Failure", {
+                          cause: {
+                            MEL_EXN_ID: "Failure",
+                            _1: "Invalid input line"
+                          }
+                        });
               }
               var ticker_map$1 = ticker_map !== undefined ? Caml_option.valFromOption(ticker_map) : compute_update_sequences(all_tickers);
               var value = Caml_format.caml_float_of_string(match$1.hd);
@@ -1401,17 +1418,19 @@ function process_input_line(ticker_map, all_tickers, line) {
                       Caml_option.some(ticker_map$1)
                     ];
             }
-            throw {
-                  MEL_EXN_ID: "Failure",
-                  _1: "Invalid input line",
-                  Error: new Error()
-                };
+            throw new Error("Failure", {
+                      cause: {
+                        MEL_EXN_ID: "Failure",
+                        _1: "Invalid input line"
+                      }
+                    });
           }
-          throw {
-                MEL_EXN_ID: "Failure",
-                _1: "Invalid input line",
-                Error: new Error()
-              };
+          throw new Error("Failure", {
+                    cause: {
+                      MEL_EXN_ID: "Failure",
+                      _1: "Invalid input line"
+                    }
+                  });
       case "R" :
           var match$2 = tokens.tl;
           if (match$2) {
@@ -1425,11 +1444,12 @@ function process_input_line(ticker_map, all_tickers, line) {
                       var match$5 = match$4.tl;
                       if (match$5) {
                         if (match$5.tl) {
-                          throw {
-                                MEL_EXN_ID: "Failure",
-                                _1: "Invalid input line",
-                                Error: new Error()
-                              };
+                          throw new Error("Failure", {
+                                    cause: {
+                                      MEL_EXN_ID: "Failure",
+                                      _1: "Invalid input line"
+                                    }
+                                  });
                         }
                         return [
                                 {
@@ -1439,28 +1459,31 @@ function process_input_line(ticker_map, all_tickers, line) {
                                 ticker_map
                               ];
                       }
-                      throw {
-                            MEL_EXN_ID: "Failure",
-                            _1: "Invalid input line",
-                            Error: new Error()
-                          };
+                      throw new Error("Failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Failure",
+                                  _1: "Invalid input line"
+                                }
+                              });
                     }
-                    throw {
-                          MEL_EXN_ID: "Failure",
-                          _1: "Invalid input line",
-                          Error: new Error()
-                        };
+                    throw new Error("Failure", {
+                              cause: {
+                                MEL_EXN_ID: "Failure",
+                                _1: "Invalid input line"
+                              }
+                            });
                 case "-" :
                     var match$6 = match$3.tl;
                     if (match$6) {
                       var match$7 = match$6.tl;
                       if (match$7) {
                         if (match$7.tl) {
-                          throw {
-                                MEL_EXN_ID: "Failure",
-                                _1: "Invalid input line",
-                                Error: new Error()
-                              };
+                          throw new Error("Failure", {
+                                    cause: {
+                                      MEL_EXN_ID: "Failure",
+                                      _1: "Invalid input line"
+                                    }
+                                  });
                         }
                         return [
                                 {
@@ -1470,24 +1493,27 @@ function process_input_line(ticker_map, all_tickers, line) {
                                 ticker_map
                               ];
                       }
-                      throw {
-                            MEL_EXN_ID: "Failure",
-                            _1: "Invalid input line",
-                            Error: new Error()
-                          };
+                      throw new Error("Failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Failure",
+                                  _1: "Invalid input line"
+                                }
+                              });
                     }
-                    throw {
-                          MEL_EXN_ID: "Failure",
-                          _1: "Invalid input line",
-                          Error: new Error()
-                        };
+                    throw new Error("Failure", {
+                              cause: {
+                                MEL_EXN_ID: "Failure",
+                                _1: "Invalid input line"
+                              }
+                            });
                 case "S" :
                     if (match$3.tl) {
-                      throw {
-                            MEL_EXN_ID: "Failure",
-                            _1: "Invalid input line",
-                            Error: new Error()
-                          };
+                      throw new Error("Failure", {
+                                cause: {
+                                  MEL_EXN_ID: "Failure",
+                                  _1: "Invalid input line"
+                                }
+                              });
                     }
                     return [
                             {
@@ -1502,39 +1528,44 @@ function process_input_line(ticker_map, all_tickers, line) {
                             ticker_map
                           ];
                 default:
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "Invalid input line",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "Invalid input line"
+                            }
+                          });
               }
             } else {
-              throw {
-                    MEL_EXN_ID: "Failure",
-                    _1: "Invalid input line",
-                    Error: new Error()
-                  };
+              throw new Error("Failure", {
+                        cause: {
+                          MEL_EXN_ID: "Failure",
+                          _1: "Invalid input line"
+                        }
+                      });
             }
           } else {
-            throw {
-                  MEL_EXN_ID: "Failure",
-                  _1: "Invalid input line",
-                  Error: new Error()
-                };
+            throw new Error("Failure", {
+                      cause: {
+                        MEL_EXN_ID: "Failure",
+                        _1: "Invalid input line"
+                      }
+                    });
           }
       default:
-        throw {
-              MEL_EXN_ID: "Failure",
-              _1: "Invalid input line",
-              Error: new Error()
-            };
+        throw new Error("Failure", {
+                  cause: {
+                    MEL_EXN_ID: "Failure",
+                    _1: "Invalid input line"
+                  }
+                });
     }
   } else {
-    throw {
-          MEL_EXN_ID: "Failure",
-          _1: "Invalid input line",
-          Error: new Error()
-        };
+    throw new Error("Failure", {
+              cause: {
+                MEL_EXN_ID: "Failure",
+                _1: "Invalid input line"
+              }
+            });
   }
 }
 
diff --git a/jscomp/test/dist/jscomp/test/topsort_test.js b/jscomp/test/dist/jscomp/test/topsort_test.js
index 4c3e9204d3..93a37bb59a 100644
--- a/jscomp/test/dist/jscomp/test/topsort_test.js
+++ b/jscomp/test/dist/jscomp/test/topsort_test.js
@@ -122,15 +122,16 @@ if (!Caml_obj.caml_equal(dfs1({
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/topsort_test.ml",
-          29,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/topsort_test.ml",
+                29,
+                2
+              ]
+            }
+          });
 }
 
 Stdlib.print_newline(undefined);
@@ -160,15 +161,16 @@ if (!Caml_obj.caml_equal(dfs1({
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/topsort_test.ml",
-          32,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/topsort_test.ml",
+                32,
+                2
+              ]
+            }
+          });
 }
 
 function dfs2(nodes, graph, visited) {
@@ -221,15 +223,16 @@ if (!Caml_obj.caml_equal(dfs2({
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/topsort_test.ml",
-          47,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/topsort_test.ml",
+                47,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(dfs2({
@@ -257,15 +260,16 @@ if (!Caml_obj.caml_equal(dfs2({
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/topsort_test.ml",
-          48,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/topsort_test.ml",
+                48,
+                2
+              ]
+            }
+          });
 }
 
 function dfs3(nodes, graph) {
@@ -315,15 +319,16 @@ if (!Caml_obj.caml_equal(dfs3({
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/topsort_test.ml",
-          65,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/topsort_test.ml",
+                65,
+                2
+              ]
+            }
+          });
 }
 
 if (!Caml_obj.caml_equal(dfs3({
@@ -351,15 +356,16 @@ if (!Caml_obj.caml_equal(dfs3({
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/topsort_test.ml",
-          66,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/topsort_test.ml",
+                66,
+                2
+              ]
+            }
+          });
 }
 
 var grwork = {
@@ -440,15 +446,16 @@ if (!Caml_obj.caml_equal(unsafe_topsort(grwork), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/topsort_test.ml",
-          110,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/topsort_test.ml",
+                110,
+                2
+              ]
+            }
+          });
 }
 
 var funarg = {
@@ -488,17 +495,19 @@ function bal(l, v, r) {
       if (lr) {
         return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
       }
-      throw {
-            MEL_EXN_ID: "Invalid_argument",
-            _1: "Set.bal",
-            Error: new Error()
-          };
+      throw new Error("Invalid_argument", {
+                cause: {
+                  MEL_EXN_ID: "Invalid_argument",
+                  _1: "Set.bal"
+                }
+              });
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
   if (hr <= (hl + 2 | 0)) {
     return /* Node */{
@@ -518,17 +527,19 @@ function bal(l, v, r) {
     if (rl) {
       return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
     }
-    throw {
-          MEL_EXN_ID: "Invalid_argument",
-          _1: "Set.bal",
-          Error: new Error()
-        };
+    throw new Error("Invalid_argument", {
+              cause: {
+                MEL_EXN_ID: "Invalid_argument",
+                _1: "Set.bal"
+              }
+            });
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.bal",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.bal"
+            }
+          });
 }
 
 function add(x, t) {
@@ -617,10 +628,11 @@ function min_elt(_param) {
       _param = l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -649,10 +661,11 @@ function max_elt(_param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -679,11 +692,12 @@ function remove_min_elt(param) {
       return param.r;
     }
   }
-  throw {
-        MEL_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
+  throw new Error("Invalid_argument", {
+            cause: {
+              MEL_EXN_ID: "Invalid_argument",
+              _1: "Set.remove_min_elt"
+            }
+          });
 }
 
 function concat(t1, t2) {
@@ -1165,10 +1179,11 @@ function find(x, _param) {
       _param = c < 0 ? param.l : param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1199,10 +1214,11 @@ function find_first(f, _param) {
       _param = param.r;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1264,10 +1280,11 @@ function find_last(f, _param) {
       _param = param.l;
       continue ;
     }
-    throw {
-          MEL_EXN_ID: Stdlib.Not_found,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.Not_found, {
+              cause: {
+                MEL_EXN_ID: Stdlib.Not_found
+              }
+            });
   };
 }
 
@@ -1482,15 +1499,16 @@ function of_list(l) {
                   match$4[1]
                 ];
         }
-        throw {
-              MEL_EXN_ID: "Assert_failure",
-              _1: [
-                "jscomp/stdlib/set.ml",
-                571,
-                18
-              ],
-              Error: new Error()
-            };
+        throw new Error("Assert_failure", {
+                  cause: {
+                    MEL_EXN_ID: "Assert_failure",
+                    _1: [
+                      "jscomp/stdlib/set.ml",
+                      571,
+                      18
+                    ]
+                  }
+                });
       };
       return sub(Stdlib__List.length(l$1), l$1)[0];
     } else {
@@ -1666,14 +1684,15 @@ function pathsort(graph) {
     var stack = param[1];
     var set = param[0];
     if (Curry._2(mem, node, set)) {
-      throw {
-            MEL_EXN_ID: Cycle,
-            _1: {
-              hd: node,
-              tl: stack
-            },
-            Error: new Error()
-          };
+      throw new Error(Cycle, {
+                cause: {
+                  MEL_EXN_ID: Cycle,
+                  _1: {
+                    hd: node,
+                    tl: stack
+                  }
+                }
+              });
     }
     return [
             Curry._2(add, node, set),
@@ -1724,15 +1743,16 @@ if (!Caml_obj.caml_equal(pathsort(grwork), {
           }
         }
       })) {
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/topsort_test.ml",
-          150,
-          4
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/topsort_test.ml",
+                150,
+                4
+              ]
+            }
+          });
 }
 
 try {
@@ -1743,15 +1763,16 @@ try {
         ],
         tl: grwork
       });
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/topsort_test.ml",
-          156,
-          8
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/topsort_test.ml",
+                156,
+                8
+              ]
+            }
+          });
 }
 catch (raw_exn){
   var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
@@ -1781,15 +1802,16 @@ catch (raw_exn){
     exit = 1;
   }
   if (exit === 1) {
-    throw {
-          MEL_EXN_ID: "Assert_failure",
-          _1: [
-            "jscomp/test/topsort_test.ml",
-            159,
-            11
-          ],
-          Error: new Error()
-        };
+    throw new Error("Assert_failure", {
+              cause: {
+                MEL_EXN_ID: "Assert_failure",
+                _1: [
+                  "jscomp/test/topsort_test.ml",
+                  159,
+                  11
+                ]
+              }
+            });
   }
   
 }
diff --git a/jscomp/test/dist/jscomp/test/tscanf_test.js b/jscomp/test/dist/jscomp/test/tscanf_test.js
index 55e9751b7a..d97924bc97 100644
--- a/jscomp/test/dist/jscomp/test/tscanf_test.js
+++ b/jscomp/test/dist/jscomp/test/tscanf_test.js
@@ -912,15 +912,16 @@ function verify_read(c) {
             }), id) === c) {
     return ;
   }
-  throw {
-        MEL_EXN_ID: "Assert_failure",
-        _1: [
-          "jscomp/test/tscanf_test.ml",
-          174,
-          2
-        ],
-        Error: new Error()
-      };
+  throw new Error("Assert_failure", {
+            cause: {
+              MEL_EXN_ID: "Assert_failure",
+              _1: [
+                "jscomp/test/tscanf_test.ml",
+                174,
+                2
+              ]
+            }
+          });
 }
 
 function verify_scan_Chars(param) {
@@ -1739,11 +1740,12 @@ function scan_elems$1(ib, accu) {
                             });
                 }
                 if (c !== 93) {
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "scan_elems",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "scan_elems"
+                            }
+                          });
                 }
                 return Stdlib__List.rev({
                             hd: i,
@@ -1830,11 +1832,12 @@ function scan_elems$2(ib, accu) {
                               });
                   }
                   console.log(Caml_bytes.bytes_to_string(Stdlib__Bytes.make(1, c)));
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "scan_elems",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "scan_elems"
+                            }
+                          });
                 }));
   }
   catch (raw_exn){
@@ -1853,7 +1856,9 @@ function scan_elems$2(ib, accu) {
     if (exn.MEL_EXN_ID === Stdlib.End_of_file) {
       return accu;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -2057,11 +2062,12 @@ function scan_rest(ib, accu) {
                               }));
                 }
                 if (c !== 93) {
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "scan_rest",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "scan_rest"
+                            }
+                          });
                 }
                 return accu;
               }));
@@ -2084,11 +2090,12 @@ function scan_elems$4(ib, accu) {
                   _1: " %c "
                 }), (function (c) {
                 if (c !== 91) {
-                  throw {
-                        MEL_EXN_ID: "Failure",
-                        _1: "scan_elems",
-                        Error: new Error()
-                      };
+                  throw new Error("Failure", {
+                            cause: {
+                              MEL_EXN_ID: "Failure",
+                              _1: "scan_elems"
+                            }
+                          });
                 }
                 if (Caml_obj.caml_equal(accu, /* [] */0)) {
                   return Curry._1(Stdlib__Scanf.bscanf(ib, /* Format */{
@@ -2129,11 +2136,12 @@ function scan_elems$4(ib, accu) {
                                 }
                               }));
                 }
-                throw {
-                      MEL_EXN_ID: "Failure",
-                      _1: "scan_elems",
-                      Error: new Error()
-                    };
+                throw new Error("Failure", {
+                          cause: {
+                            MEL_EXN_ID: "Failure",
+                            _1: "scan_elems"
+                          }
+                        });
               }));
 }
 
@@ -2260,11 +2268,12 @@ function scan_rest$1(ib, accu) {
                                                         },
                                                         _1: "scan_int_list"
                                                       });
-                                                  throw {
-                                                        MEL_EXN_ID: "Failure",
-                                                        _1: s,
-                                                        Error: new Error()
-                                                      };
+                                                  throw new Error("Failure", {
+                                                            cause: {
+                                                              MEL_EXN_ID: "Failure",
+                                                              _1: s
+                                                            }
+                                                          });
                                               }
                                             }));
                               }));
@@ -2340,7 +2349,9 @@ function scan_elems$5(ib, scan_elem, accu) {
     if (exn.MEL_EXN_ID === Stdlib__Scanf.Scan_failure) {
       return accu;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
@@ -4340,10 +4351,11 @@ function next_char(ob, param) {
   var s = Stdlib__Buffer.contents(ob);
   var len = s.length;
   if (len === 0) {
-    throw {
-          MEL_EXN_ID: Stdlib.End_of_file,
-          Error: new Error()
-        };
+    throw new Error(Stdlib.End_of_file, {
+              cause: {
+                MEL_EXN_ID: Stdlib.End_of_file
+              }
+            });
   }
   var c = Caml_string.get(s, 0);
   ob.position = 0;
diff --git a/jscomp/test/dist/jscomp/test/variant.js b/jscomp/test/dist/jscomp/test/variant.js
index ccc8b275f5..5ba9ccc4af 100644
--- a/jscomp/test/dist/jscomp/test/variant.js
+++ b/jscomp/test/dist/jscomp/test/variant.js
@@ -98,7 +98,9 @@ function rollback_path(subst, p) {
         
       }
     } else {
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }
 }
@@ -135,7 +137,9 @@ function fooExn(f) {
       var match = exn._1;
       return match[0] + match[1] | 0;
     }
-    throw exn;
+    throw new Error(exn.MEL_EXN_ID, {
+              cause: exn
+            });
   }
 }
 
diff --git a/test/blackbox-tests/exn-cause.t b/test/blackbox-tests/exn-cause.t
new file mode 100644
index 0000000000..167c0e6fb2
--- /dev/null
+++ b/test/blackbox-tests/exn-cause.t
@@ -0,0 +1,147 @@
+
+  $ . ./setup.sh
+  $ cat > dune-project <<EOF
+  > (lang dune 3.8)
+  > (using melange 0.1)
+  > EOF
+  $ cat > dune <<EOF
+  > (melange.emit
+  >  (target js-out)
+  >  (preprocess (pps melange.ppx)))
+  > EOF
+  $ cat > x.ml << EOF
+  > exception A of int
+  > let () =
+  >   let a0 =
+  >     try [%mel.raw{| (function (){throw 2} ()) |}] with
+  >     | A x -> x
+  >     | Js.Exn.Error v -> Obj.magic v
+  >     | _ -> assert false
+  >   in
+  >   Js.log a0
+  > EOF
+  $ dune build @melange
+  $ cat _build/default/js-out/x.js
+  // Generated by Melange
+  'use strict';
+  
+  var Caml_exceptions = require("melange.js/caml_exceptions.js");
+  var Caml_js_exceptions = require("melange.js/caml_js_exceptions.js");
+  var Js__Js_exn = require("melange.js/js_exn.js");
+  
+  var A = /* @__PURE__ */Caml_exceptions.create("Melange__X.A");
+  
+  var a0;
+  
+  try {
+    a0 = ((function (){throw 2} ())
+    );
+  }
+  catch (raw_exn){
+    var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
+    if (exn.MEL_EXN_ID === A || exn.MEL_EXN_ID === Js__Js_exn.$$Error) {
+      a0 = exn._1;
+    } else {
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "x.ml",
+                    7,
+                    11
+                  ]
+                }
+              });
+    }
+  }
+  
+  console.log(a0);
+  
+  exports.A = A;
+  /* a0 Not a pure module */
+  $ node _build/default/js-out/x.js
+  2
+
+Raise `null` / `undefined`
+
+  $ cat > x.ml << EOF
+  > exception A of int
+  > let () =
+  >   let a0 =
+  >     try [%mel.raw{| (function (){throw undefined} ()) |}] with
+  >     | A x -> x
+  >     | Js.Exn.Error v -> Obj.magic v
+  >     | _ -> assert false
+  >   and a1 =
+  >     try [%mel.raw{| (function (){throw null} ()) |}] with
+  >     | A x -> x
+  >     | Js.Exn.Error v -> Obj.magic v
+  >     | _ -> assert false
+  >   in
+  >   Js.log2 a0 a1
+  > EOF
+  $ dune build @melange
+  $ cat _build/default/js-out/x.js
+  // Generated by Melange
+  'use strict';
+  
+  var Caml_exceptions = require("melange.js/caml_exceptions.js");
+  var Caml_js_exceptions = require("melange.js/caml_js_exceptions.js");
+  var Js__Js_exn = require("melange.js/js_exn.js");
+  
+  var A = /* @__PURE__ */Caml_exceptions.create("Melange__X.A");
+  
+  var a0;
+  
+  try {
+    a0 = ((function (){throw undefined} ())
+    );
+  }
+  catch (raw_exn){
+    var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
+    if (exn.MEL_EXN_ID === A || exn.MEL_EXN_ID === Js__Js_exn.$$Error) {
+      a0 = exn._1;
+    } else {
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "x.ml",
+                    7,
+                    11
+                  ]
+                }
+              });
+    }
+  }
+  
+  var a1;
+  
+  try {
+    a1 = ((function (){throw null} ())
+    );
+  }
+  catch (raw_exn$1){
+    var exn$1 = Caml_js_exceptions.internalToOCamlException(raw_exn$1);
+    if (exn$1.MEL_EXN_ID === A || exn$1.MEL_EXN_ID === Js__Js_exn.$$Error) {
+      a1 = exn$1._1;
+    } else {
+      throw new Error("Assert_failure", {
+                cause: {
+                  MEL_EXN_ID: "Assert_failure",
+                  _1: [
+                    "x.ml",
+                    12,
+                    11
+                  ]
+                }
+              });
+    }
+  }
+  
+  console.log(a0, a1);
+  
+  exports.A = A;
+  /* a0 Not a pure module */
+  $ node _build/default/js-out/x.js
+  undefined null
diff --git a/test/blackbox-tests/mel-as-inline-records.t b/test/blackbox-tests/mel-as-inline-records.t
index 2250061e2e..b60bf8ec7b 100644
--- a/test/blackbox-tests/mel-as-inline-records.t
+++ b/test/blackbox-tests/mel-as-inline-records.t
@@ -23,11 +23,12 @@ Test `@mel.as` in inline records / record extensions
   
   function user3(param) {
     try {
-      throw {
-            MEL_EXN_ID: UserException,
-            renamed: "Corentin",
-            Error: new Error()
-          };
+      throw new Error(UserException, {
+                cause: {
+                  MEL_EXN_ID: UserException,
+                  renamed: "Corentin"
+                }
+              });
     }
     catch (raw_exn){
       var exn = Caml_js_exceptions.internalToOCamlException(raw_exn);
@@ -35,7 +36,9 @@ Test `@mel.as` in inline records / record extensions
         console.log("name:", exn.renamed);
         return ;
       }
-      throw exn;
+      throw new Error(exn.MEL_EXN_ID, {
+                cause: exn
+              });
     }
   }