JS: keep assignments with side-effects when removing let/const declar…

…ation in block, fixes #487
tdewolff · Jun 4, 2022 · c1fb3fc · c1fb3fc
1 parent b31a40e
commit c1fb3fc
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Showing 2 changed files with 18 additions and 5 deletions.
diff --git a/js/js_test.go b/js/js_test.go
@@ -770,6 +770,7 @@ func TestJS(t *testing.T) {
 		{`var a=1;g();a=2;let b=3`, `var a=1;g(),a=2;let b=3`},                                                                                             // #474
 		{`if(!(0<1&&1<2)){throw new Error()}`, `if(!(0<1&&1<2))throw new Error`},                                                                           // #479
 		{`class A{set x(e){}}`, `class A{set x(e){}}`},                                                                                                     // #481
+		{`if(a){let b=c(d)}`, `a&&c(d)`},                                                                                                                   // #487
 	}
 
 	m := minify.New()

diff --git a/js/stmtlist.go b/js/stmtlist.go
@@ -111,12 +111,24 @@ func optimizeStmt(i js.IStmt) js.IStmt {
 		// merge body and remove braces if it is not a lexical declaration
 		blockStmt.List = optimizeStmtList(blockStmt.List, defaultBlock)
 		if len(blockStmt.List) == 1 {
-			varDecl, isVarDecl := blockStmt.List[0].(*js.VarDecl)
-			_, isClassDecl := blockStmt.List[0].(*js.ClassDecl)
-			if !isClassDecl && (!isVarDecl || varDecl.TokenType == js.VarToken) {
-				return optimizeStmt(blockStmt.List[0])
+			if _, ok := blockStmt.List[0].(*js.ClassDecl); ok {
+				return &js.EmptyStmt{}
+			} else if varDecl, ok := blockStmt.List[0].(*js.VarDecl); ok && varDecl.TokenType != js.VarToken {
+				// remove let or const declaration in otherwise empty scope, but keep assignments
+				exprs := []js.IExpr{}
+				for _, item := range varDecl.List {
+					if item.Default != nil && hasSideEffects(item.Default) {
+						exprs = append(exprs, item.Default)
+					}
+				}
+				if len(exprs) == 0 {
+					return &js.EmptyStmt{}
+				} else if len(exprs) == 1 {
+					return &js.ExprStmt{exprs[0]}
+				}
+				return &js.ExprStmt{&js.CommaExpr{exprs}}
 			}
-			return &js.EmptyStmt{}
+			return optimizeStmt(blockStmt.List[0])
 		} else if len(blockStmt.List) == 0 {
 			return &js.EmptyStmt{}
 		}