JS: change undefined=>0[0] and void 0=>0[0], see #790

Author: tdewolff

js/js.go

@@ -863,10 +863,10 @@ func (m *jsMinifier) minifyExpr(i js.IExpr, prec js.OpPrec) {
 		}
 		data := expr.Data
 		if bytes.Equal(data, undefinedBytes) { // TODO: only if not defined
-			if js.OpUnary < prec {
-				m.write(groupedVoidZeroBytes)
+			if js.OpMember < prec {
+				m.write(groupedZeroIndexBytes)
 			} else {
-				m.write(voidZeroBytes)
+				m.write(zeroIndexBytes)
 			}
 		} else if bytes.Equal(data, infinityBytes) { // TODO: only if not defined
 			if js.OpMul < prec {
@@ -997,6 +997,8 @@ func (m *jsMinifier) minifyExpr(i js.IExpr, prec js.OpPrec) {
 		if expr.Op == js.PostIncrToken || expr.Op == js.PostDecrToken {
 			m.minifyExpr(expr.X, unaryPrecMap[expr.Op])
 			m.write(expr.Op.Bytes())
+		} else if expr.Op == js.VoidToken && !hasSideEffects(expr.X) {
+			m.write(zeroIndexBytes)
 		} else {
 			isLtNot := expr.Op == js.NotToken && 0 < len(m.prev) && m.prev[len(m.prev)-1] == '<'
 			m.write(expr.Op.Bytes())

js/js_test.go

@@ -186,20 +186,21 @@ func TestJS(t *testing.T) {
 		{`x=false`, `x=!1`},
 		{`x=false()`, `x=(!1)()`},
 		{`false`, `!1`},
-		{`x=undefined`, `x=void 0`},
-		{`x=undefined()`, `x=(void 0)()`},
-		{`x=undefined.a`, `x=(void 0).a`},
+		{`x=void 0`, `x=0[0]`},
+		{`x=undefined`, `x=0[0]`},
+		{`x=undefined()`, `x=0[0]()`},
+		{`x=undefined.a`, `x=0[0].a`},
 		//{`{const undefined=5;x=undefined}`, `{const undefined=5;x=undefined}`},
 		{`x=Infinity`, `x=1/0`},
 		{`x=Infinity()`, `x=(1/0)()`},
 		{`x=2**Infinity`, `x=2**(1/0)`},
 		//{`{const Infinity=5;x=Infinity}`, `{const Infinity=5;x=Infinity}`},
 		{`!""`, `!0`},
 		{`!"foobar"`, `!1`},
-		{`class a extends undefined {}`, `class a extends(void 0){}`},
+		{`class a extends undefined {}`, `class a extends 0[0]{}`},
 		{`new true`, `new(!0)`},
 		{`function*a(){yield undefined}`, `function*a(){yield}`},
-		{`function*a(){yield*undefined}`, `function*a(){yield*void 0}`},
+		{`function*a(){yield*undefined}`, `function*a(){yield*0[0]}`},
 
 		// if/else statements
 		{`function f(){if(a){return b}}`, `function f(){if(a)return b}`},

js/util.go

@@ -73,8 +73,8 @@ var (
 	undefinedBytes             = []byte("undefined")
 	infinityBytes              = []byte("Infinity")
 	nullBytes                  = []byte("null")
-	voidZeroBytes              = []byte("void 0")
-	groupedVoidZeroBytes       = []byte("(void 0)")
+	zeroIndexBytes             = []byte("0[0]")
+	groupedZeroIndexBytes      = []byte("(0[0])")
 	oneDivZeroBytes            = []byte("1/0")
 	groupedOneDivZeroBytes     = []byte("(1/0)")
 	notZeroBytes               = []byte("!0")