Issue 7202 - Add hasListeners method to EventEmitter

lib/events.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 17 matching lines @@
   }
 
   /**
    * Adds a listener for the specified event name.
    *
    * @param {string}   name
    * @param {function} listener
    */
   on(name, listener)
   {
-    let listeners = this._listeners.size > 0 ? this._listeners.get(name) : null;
+    let listeners = this._listeners.get(name);
     if (listeners)
       listeners.push(listener);
     else
       this._listeners.set(name, [listener]);
   }
 
   /**
    * Removes a listener for the specified event name.
    *
    * @param {string}   name
    * @param {function} listener
    */
   off(name, listener)
   {
-    let listeners = this._listeners.size > 0 ? this._listeners.get(name) : null;
+    let listeners = this._listeners.get(name);
     if (listeners)
     {
       if (listeners.length > 1)
       {
         let idx = listeners.indexOf(listener);
         if (idx != -1)
           listeners.splice(idx, 1);
       }
       else if (listeners[0] === listener)
       {
@@ skipping 61 matching lines @@
     let listeners = this._listeners.size > 0 ? this._listeners.get(name) : null;
     if (listeners)
     {
       for (let listener of listeners.slice())
         listener(...args);
     }
   }
 }
 
 exports.EventEmitter = EventEmitter;