[fix] Prevent on<event> setters from removing all listeners

lib/WebSocket.js

@@ -219,6 +219,8 @@ class WebSocket extends EventEmitter {
    */
   emitClose () {
     this.readyState = WebSocket.CLOSED;
+    // emit 'cleanup' before 'close' because close will change attributes
+    // and closed ws-sockets will not be found 'WebSocketServer.clients'  js-Set collection
     this.emit('close', this._closeCode || 1006, this._closeMessage || '');
 
     if (this.extensions[PerMessageDeflate.extensionName]) {
@@ -409,8 +411,10 @@ WebSocket.CLOSED = 3;
      * @public
      */
     get () {
-      const listener = this.listeners(method)[0];
-      return listener ? listener._listener ? listener._listener : listener : undefined;
+      const listeners = this.listeners(method);
+      for (var i = 0; i < listeners.length; i++) {
+        if (listeners[i]._listener) return listeners[i]._listener;
+      }
     },
     /**
      * Add a listener for the event.
@@ -419,7 +423,11 @@ WebSocket.CLOSED = 3;
      * @public
      */
     set (listener) {
-      this.removeAllListeners(method);
+      const listeners = this.listeners(method);
+      for (var i = 0; i < listeners.length; i++) {
+        /* listeners added outside usage of 'addEventListeners' are not removed */
+        if (listeners[i]._listener) this.removeListener(method, listeners[i]);
+      }
       this.addEventListener(method, listener);
     }
   });