fix(ext/websocket): initialize error attribute of WebSocket ErrorEvent (#26796)

Fixes #26216

Not required by the spec but Discord.js depends on it, see
#26216 (comment)

Author: littledivy

ext/websocket/01_websocket.js

@@ -28,6 +28,7 @@ const {
   ArrayPrototypePush,
   ArrayPrototypeShift,
   ArrayPrototypeSome,
+  Error,
   ErrorPrototypeToString,
   ObjectDefineProperties,
   ObjectPrototypeIsPrototypeOf,
@@ -488,8 +489,11 @@ class WebSocket extends EventTarget {
           /* error */
           this[_readyState] = CLOSED;
 
+          const message = op_ws_get_error(rid);
+          const error = new Error(message);
           const errorEv = new ErrorEvent("error", {
-            message: op_ws_get_error(rid),
+            error,
+            message,
           });
           this.dispatchEvent(errorEv);
 

tests/unit/websocket_test.ts

@@ -453,7 +453,8 @@ Deno.test("invalid server", async () => {
   const { promise, resolve } = Promise.withResolvers<void>();
   const ws = new WebSocket("ws://localhost:2121");
   let err = false;
-  ws.onerror = () => {
+  ws.onerror = (e) => {
+    assert("error" in e);
     err = true;
   };
   ws.onclose = () => {