AS2 Event Dispatcher in JS

event.js

(function(window){

  var EventDispatcher = window.EventDispatcher = function(scope){
    this.scope = scope;
    this.listeners = {};
  };

  EventDispatcher.prototype.addEventListener = function(type, listener){
    if (listener instanceof Function) {
      if(!this.listeners[type]) {
        this.listeners[type] = [listener];
      } else {
        this.listeners[type].push(listener);
      }
    }
  };

  EventDispatcher.prototype.hasEventListener = function(type){
    return (typeof this.listeners[type] != "undefined");
  };

  EventDispatcher.prototype.removeEventListener = function(type, listener){
    if (this.hasEventListener(type)) {
      var len = this.listeners[type].length, i = 0;
      for (; i<len; i++) {
        if (this.listeners[type][i] == listener) {
          this.listeners.splice(i, 1);
        }
      }
    }
  };

  EventDispatcher.prototype.dispatchEvent = function(type, args){
    if (this.hasEventListener(type)) {
      var len = this.listeners[type].length, i = 0;
      for (; i<len; i++) {
        this.listeners[type][i].apply(this.scope, [args]);
      }
    }
  };

})(window);