Implement Number.toFixed (#1413)

Author: Dimava

src/LuaLib.ts

@@ -58,6 +58,7 @@ export enum LuaLibFeature {
     NumberIsFinite = "NumberIsFinite",
     NumberIsNaN = "NumberIsNaN",
     NumberToString = "NumberToString",
+    NumberToFixed = "NumberToFixed",
     ObjectAssign = "ObjectAssign",
     ObjectDefineProperty = "ObjectDefineProperty",
     ObjectEntries = "ObjectEntries",

src/lualib/NumberToFixed.ts

@@ -0,0 +1,14 @@
+/// https://www.ecma-international.org/ecma-262/10.0/index.html#sec-number.prototype.tofixed
+export function __TS__NumberToFixed(this: number, fractionDigits?: number): string {
+    if (Math.abs(this) >= 1e21 || this !== this) {
+        return this.toString();
+    }
+    const f = Math.floor(fractionDigits ?? 0);
+    // reduced to 99 as string.format only supports 2-digit numbers
+    if (f < 0 || f > 99) {
+        throw "toFixed() digits argument must be between 0 and 99";
+    }
+    // throws "invalid format (width or precision too long)" if strlen > 99
+    // if (f < 80) return fmt; else try {return fmt} catch(_) { throw "toFixed() digits argument..." }
+    return string.format(`%.${f}f`, this);
+}

src/transformation/builtins/number.ts

@@ -20,6 +20,8 @@ export function transformNumberPrototypeCall(
             return params.length === 0
                 ? lua.createCallExpression(lua.createIdentifier("tostring"), [caller], node)
                 : transformLuaLibFunction(context, LuaLibFeature.NumberToString, node, caller, ...params);
+        case "toFixed":
+            return transformLuaLibFunction(context, LuaLibFeature.NumberToFixed, node, caller, ...params);
         default:
             context.diagnostics.push(unsupportedProperty(calledMethod.name, "number", expressionName));
     }

test/unit/builtins/numbers.spec.ts

@@ -69,6 +69,26 @@ test.each([
     util.testExpressionTemplate`(${value}).toString(2)`.expectToEqual(luaNativeSpecialNumString);
 });
 
+const toFixedFractions = [undefined, 0, 1, 2, Math.PI, 5, 99];
+// 1.5, 1.25 and 1.125 fails as rounding differ
+const toFixedValues = [-1, 0, 1, Math.PI, -1.1234, -9.99e19, 1e22];
+const toFixedPairs = toFixedValues.flatMap(value => toFixedFractions.map(frac => [value, frac] as const));
+test.each(toFixedPairs)("(%p).toFixed(%p)", (value, frac) => {
+    util.testExpressionTemplate`(${value}).toFixed(${frac})`.expectToMatchJsResult();
+});
+
+test.each([
+    [NaN, "(0/0)"],
+    [Infinity, "(1/0)"],
+    [-Infinity, "(-(1/0))"],
+])("%p.toFixed(2)", (value, luaNativeSpecialNum) => {
+    // Need to get the actual lua tostring version of inf/nan
+    // this is platform dependent so we can/should not hardcode it
+    const luaNativeSpecialNumString = util.testExpression`${luaNativeSpecialNum}.toString()`.getLuaExecutionResult();
+    // Cannot use expectToMatchJsResult because this actually wont be the same in JS in Lua
+    util.testExpressionTemplate`(${value}).toFixed(2)`.expectToEqual(luaNativeSpecialNumString);
+});
+
 test.each(cases)("isNaN(%p)", value => {
     util.testExpressionTemplate`isNaN(${value} as any)`.expectToMatchJsResult();
 });