Do not remove default_arg = undefined, as it changes Function.length. C…

…loses #1295
terser · Feb 12, 2023 · ca51c11 · ca51c11
1 parent 12b7709
commit ca51c11
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Showing 2 changed files with 22 additions and 1 deletion.
diff --git a/lib/compress/index.js b/lib/compress/index.js
@@ -2764,7 +2764,13 @@ def_optimize(AST_DefaultAssign, function(self, compressor) {
     var evaluateRight = self.right.evaluate(compressor);
 
     // `[x = undefined] = foo` ---> `[x] = foo`
-    if (evaluateRight === undefined) {
+    // `(arg = undefined) => ...` ---> `(arg) => ...` (unless `keep_fargs`)
+    if (
+        evaluateRight === undefined &&
+        (compressor.parent() instanceof AST_Lambda
+            ? compressor.option("keep_fargs") === false
+            : true)
+    ) {
         self = self.left;
     } else if (evaluateRight !== self.right) {
         evaluateRight = make_node_from_constant(evaluateRight, self.right);

diff --git a/test/compress/parameters.js b/test/compress/parameters.js
@@ -184,6 +184,21 @@ default_arguments: {
     expect_exact: "function x(a=6){}function x(a=6+5){}function x({foo}={},[bar]=[1]){}"
 }
 
+keep_default_arg_when_undefined: {
+    options = {
+        keep_fargs: true,
+        evaluate: true,
+    }
+    input: {
+        function x(a = void 0) { }
+        console.log(x.length)
+    }
+    expect: {
+        function x(a = undefined) { }
+        console.log(x.length)
+    }
+}
+
 default_values_in_destructurings: {
     beautify = {
         ecma: 2015