[major] Ignore listeners not added with WebSocket#addEventListener()

Make `WebSocket.prototype.removeEventListener()` only remove listeners
added with `WebSocket.prototype.addEventListener()` and only one at
time.

doc/ws.md

@@ -476,7 +476,9 @@ The current state of the connection. This is one of the ready state constants.
 - `type` {String} A string representing the event type to remove.
 - `listener` {Function} The listener to remove.
 
-Removes an event listener emulating the `EventTarget` interface.
+Removes an event listener emulating the `EventTarget` interface. This method
+only removes listeners added with
+[`websocket.addEventListener()`](#websocketaddeventlistenertype-listener-options).
 
 ### websocket.send(data[, options][, callback])
 

lib/event-target.js

@@ -173,8 +173,9 @@ const EventTarget = {
    */
   removeEventListener(type, handler) {
     for (const listener of this.listeners(type)) {
-      if (listener === handler || listener[kListener] === handler) {
+      if (listener[kListener] === handler) {
         this.removeListener(type, listener);
+        break;
       }
     }
   }

test/websocket.test.js

@@ -2233,6 +2233,30 @@ describe('WebSocket', () => {
 
       assert.strictEqual(ws.listenerCount('message'), 0);
       assert.strictEqual(ws.listenerCount('open'), 0);
+
+      // Multiple listeners.
+      ws.addEventListener('message', NOOP);
+      ws.addEventListener('message', NOOP);
+
+      assert.strictEqual(ws.listeners('message')[0][kListener], NOOP);
+      assert.strictEqual(ws.listeners('message')[1][kListener], NOOP);
+
+      ws.removeEventListener('message', NOOP);
+
+      assert.strictEqual(ws.listeners('message')[0][kListener], NOOP);
+
+      ws.removeEventListener('message', NOOP);
+
+      assert.strictEqual(ws.listenerCount('message'), 0);
+
+      // Listeners not added with `websocket.addEventListener()`.
+      ws.on('message', NOOP);
+
+      assert.deepStrictEqual(ws.listeners('message'), [NOOP]);
+
+      ws.removeEventListener('message', NOOP);
+
+      assert.deepStrictEqual(ws.listeners('message'), [NOOP]);
     });
 
     it('wraps text data in a `MessageEvent`', (done) => {