lib: add ability to add separate event name to defineEventHandler

lib/internal/event_target.js

@@ -1022,12 +1022,12 @@ function makeEventHandler(handler) {
   return eventHandler;
 }
 
-function defineEventHandler(emitter, name) {
+function defineEventHandler(emitter, name, event = name) {
   // 8.1.5.1 Event handlers - basically `on[eventName]` attributes
   const propName = `on${name}`;
   function get() {
     validateInternalField(this, kHandlers, 'EventTarget');
-    return this[kHandlers]?.get(name)?.handler ?? null;
+    return this[kHandlers]?.get(event)?.handler ?? null;
   }
   ObjectDefineProperty(get, 'name', {
     __proto__: null,
@@ -1036,24 +1036,24 @@ function defineEventHandler(emitter, name) {
 
   function set(value) {
     validateInternalField(this, kHandlers, 'EventTarget');
-    let wrappedHandler = this[kHandlers]?.get(name);
+    let wrappedHandler = this[kHandlers]?.get(event);
     if (wrappedHandler) {
       if (typeof wrappedHandler.handler === 'function') {
-        this[kEvents].get(name).size--;
-        const size = this[kEvents].get(name).size;
-        this[kRemoveListener](size, name, wrappedHandler.handler, false);
+        this[kEvents].get(event).size--;
+        const size = this[kEvents].get(event).size;
+        this[kRemoveListener](size, event, wrappedHandler.handler, false);
       }
       wrappedHandler.handler = value;
       if (typeof wrappedHandler.handler === 'function') {
-        this[kEvents].get(name).size++;
-        const size = this[kEvents].get(name).size;
-        this[kNewListener](size, name, value, false, false, false, false);
+        this[kEvents].get(event).size++;
+        const size = this[kEvents].get(event).size;
+        this[kNewListener](size, event, value, false, false, false, false);
       }
     } else {
       wrappedHandler = makeEventHandler(value);
-      this.addEventListener(name, wrappedHandler);
+      this.addEventListener(event, wrappedHandler);
     }
-    this[kHandlers].set(name, wrappedHandler);
+    this[kHandlers].set(event, wrappedHandler);
   }
   ObjectDefineProperty(set, 'name', {
     __proto__: null,

test/parallel/test-eventtarget.js

@@ -614,6 +614,15 @@ let asyncTest = Promise.resolve();
   target.dispatchEvent(new Event('foo'));
   deepStrictEqual(output, [1, 2, 3, 4]);
 }
+{
+  const target = new EventTarget();
+  defineEventHandler(target, 'foo', 'bar');
+  const output = [];
+  target.addEventListener('bar', () => output.push(1));
+  target.onfoo = () => output.push(2);
+  target.dispatchEvent(new Event('bar'));
+  deepStrictEqual(output, [1, 2]);
+}
 {
   const et = new EventTarget();
   const listener = common.mustNotCall();