From 2c39961d4e9ebd2d066d012ddc8129f751384bac Mon Sep 17 00:00:00 2001
From: Chengzhong Wu <cwu631@bloomberg.net>
Date: Fri, 29 Aug 2025 18:14:49 +0100
Subject: [PATCH] lib: fix DOMException subclass support

---
 lib/internal/per_context/domexception.js    |  6 +--
 test/parallel/test-domexception-subclass.js | 55 +++++++++++++++++++++
 2 files changed, 58 insertions(+), 3 deletions(-)
 create mode 100644 test/parallel/test-domexception-subclass.js

diff --git a/lib/internal/per_context/domexception.js b/lib/internal/per_context/domexception.js
index 1bc46616556612..d8a2e7df88a697 100644
--- a/lib/internal/per_context/domexception.js
+++ b/lib/internal/per_context/domexception.js
@@ -60,7 +60,6 @@ const disusedNamesSet = new SafeSet()
   .add('NoDataAllowedError')
   .add('ValidationError');
 
-let DOMExceptionPrototype;
 // The DOMException WebIDL interface defines that:
 // - ObjectGetPrototypeOf(DOMException) === Function.
 // - ObjectGetPrototypeOf(DOMException.prototype) === Error.prototype.
@@ -75,7 +74,8 @@ class DOMException {
     // internal slot.
     // eslint-disable-next-line no-restricted-syntax
     const self = new Error();
-    ObjectSetPrototypeOf(self, DOMExceptionPrototype);
+    // Use `new.target.prototype` to support DOMException subclasses.
+    ObjectSetPrototypeOf(self, new.target.prototype);
     self[transfer_mode_private_symbol] = kCloneable;
 
     if (options && typeof options === 'object') {
@@ -158,7 +158,7 @@ class DOMException {
   }
 }
 
-DOMExceptionPrototype = DOMException.prototype;
+const DOMExceptionPrototype = DOMException.prototype;
 ObjectSetPrototypeOf(DOMExceptionPrototype, ErrorPrototype);
 ObjectDefineProperties(DOMExceptionPrototype, {
   [SymbolToStringTag]: { __proto__: null, configurable: true, value: 'DOMException' },
diff --git a/test/parallel/test-domexception-subclass.js b/test/parallel/test-domexception-subclass.js
new file mode 100644
index 00000000000000..a9498d95a13d5c
--- /dev/null
+++ b/test/parallel/test-domexception-subclass.js
@@ -0,0 +1,55 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+class MyDOMException extends DOMException {
+  ownProp;
+  #reason;
+
+  constructor() {
+    super('my message', 'NotFoundError');
+    this.ownProp = 'bar';
+    this.#reason = 'hello';
+  }
+
+  get reason() {
+    return this.#reason;
+  }
+}
+
+const myException = new MyDOMException();
+// Verifies the prototype chain
+assert(myException instanceof MyDOMException);
+assert(myException instanceof DOMException);
+assert(myException instanceof Error);
+// Verifies [[ErrorData]]
+assert(Error.isError(myException));
+
+// Verifies subclass properties
+assert(Object.hasOwn(myException, 'ownProp'));
+assert(!Object.hasOwn(myException, 'reason'));
+assert.strictEqual(myException.reason, 'hello');
+
+// Verifies error properties
+assert.strictEqual(myException.name, 'NotFoundError');
+assert.strictEqual(myException.code, 8);
+assert.strictEqual(myException.message, 'my message');
+assert.strictEqual(typeof myException.stack, 'string');
+
+// Verify structuredClone only copies known error properties.
+const cloned = structuredClone(myException);
+assert(!(cloned instanceof MyDOMException));
+assert(cloned instanceof DOMException);
+assert(cloned instanceof Error);
+assert(Error.isError(cloned));
+
+// Verify custom properties
+assert(!Object.hasOwn(cloned, 'ownProp'));
+assert.strictEqual(cloned.reason, undefined);
+
+// Verify cloned error properties
+assert.strictEqual(cloned.name, 'NotFoundError');
+assert.strictEqual(cloned.code, 8);
+assert.strictEqual(cloned.message, 'my message');
+assert.strictEqual(cloned.stack, myException.stack);