JS: fix bug when merging hoisted var-decl to let-decl, fixes #687

js/js_test.go

@@ -816,6 +816,7 @@ func TestJS(t *testing.T) {
 		{`'\u000A\u000D'`, "`\n\r`"},                           // #653
 		{`for(!a;b;c);`, "for(!a;b;c);"},                       // #656
 		{"var a = /*! comment */ b;", "/*! comment */var a=b"}, // #664
+		{`var c="";for(let i=0;;);var d="";for(let i=0;;);`, `var d,c="";for(let i=0;;);d="";for(let i=0;;);`}, // #687
 	}
 
 	m := minify.New()

js/stmtlist.go

@@ -190,11 +190,15 @@ func optimizeStmtList(list []js.IStmt, blockType blockType) []js.IStmt {
 					j--
 				} else if forStmt, ok := list[i].(*js.ForStmt); ok {
 					// TODO: only merge lhs expression that don't have 'in' or 'of' keywords (slow to check?)
-					if varDecl, ok := forStmt.Init.(*js.VarDecl); ok {
-						if len(varDecl.List) == 0 || forStmt.Init == nil {
-							forStmt.Init = left.Value
-							j--
-						} else if mergeVarDeclExprStmt(varDecl, left, true) {
+					if forStmt.Init == nil {
+						forStmt.Init = left.Value
+						j--
+					} else if decl, ok := forStmt.Init.(*js.VarDecl); ok && len(decl.List) == 0 {
+						forStmt.Init = left.Value
+						j--
+					} else if ok && (decl.TokenType == js.VarToken || decl.TokenType == js.ErrorToken) {
+						// this is the second VarDecl, so we are hoisting var declarations, which means the forInit variables are already in 'left'
+						if merge := mergeVarDeclExprStmt(decl, left, true); merge {
 							j--
 						}
 					}