events: add initEvent to Event

Refs: https://dom.spec.whatwg.org/#dom-event-initevent
PR-URL: #46069
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Zeyu "Alex" Yang <himself65@outlook.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

doc/api/events.md

@@ -2086,6 +2086,22 @@ added: v14.5.0
 
 This is not used in Node.js and is provided purely for completeness.
 
+#### `event.initEvent(type[, bubbles[, cancelable]])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 3 - Legacy: The WHATWG spec considers it deprecated and users
+> shouldn't use it at all.
+
+* `type` {string}
+* `bubbles` {boolean}
+* `cancelable` {boolean}
+
+Redundant with event constructors and incapable of setting `composed`.
+This is not used in Node.js and is provided purely for completeness.
+
 #### `event.isTrusted`
 
 <!-- YAML

lib/internal/event_target.js

@@ -123,6 +123,23 @@ class Event {
     this[kIsBeingDispatched] = false;
   }
 
+  /**
+   * @param {string} type
+   * @param {boolean} [bubbles]
+   * @param {boolean} [cancelable]
+   */
+  initEvent(type, bubbles = false, cancelable = false) {
+    if (arguments.length === 0)
+      throw new ERR_MISSING_ARGS('type');
+
+    if (this[kIsBeingDispatched]) {
+      return;
+    }
+    this[kType] = `${type}`;
+    this.#bubbles = !!bubbles;
+    this.#cancelable = !!cancelable;
+  }
+
   [customInspectSymbol](depth, options) {
     if (!isEvent(this))
       throw new ERR_INVALID_THIS('Event');
@@ -307,6 +324,7 @@ ObjectDefineProperties(
       configurable: true,
       value: 'Event',
     },
+    initEvent: kEnumerableProperty,
     stopImmediatePropagation: kEnumerableProperty,
     preventDefault: kEnumerableProperty,
     target: kEnumerableProperty,

test/wpt/status/dom/events.json

@@ -8,14 +8,6 @@
       ]
     }
   },
-  "Event-constructors.any.js": {
-    "fail": {
-      "expected": [
-        "Untitled 3",
-        "Untitled 4"
-      ]
-    }
-  },
   "Event-dispatch-listener-order.window.js": {
     "skip": "document is not defined"
   },