Custom events in JavaScript Mostly based on this excellent article http://www.nczonline.net/blog/2010/03/09/custom-events-in-javascript/

custom_events.js

function EventTarget() {
  this._listeners = {};
}

EventTarget.prototype = {
  
  constructor: EventTarget,

  addListener: function(type, listener){
      if (typeof this._listeners[type] == "undefined"){
          this._listeners[type] = [];
      }

      this._listeners[type].push(listener);
  },

  fire: function(event){
      if (typeof event == "string"){
          event = { type: event };
      }
      if (!event.target){
          event.target = this;
      }

      if (!event.type){  //falsy
          throw new Error("Event object missing 'type' property.");
      }

      if (this._listeners[event.type] instanceof Array){
          var listeners = this._listeners[event.type];
          for (var i=0, len=listeners.length; i < len; i++){
              listeners[i].call(this, event);
          }
      }
  },

  removeListener: function(type, listener){
      if (this._listeners[type] instanceof Array){
          var listeners = this._listeners[type];
          for (var i=0, len=listeners.length; i < len; i++){
              if (listeners[i] === listener){
                  listeners.splice(i, 1);
                  break;
              }
          }
      }
  }
};

var MyObject = function() {
  EventTarget.call(this);

  this.call = function() {
  	this.foo();
  }
}

MyObject.prototype = new EventTarget();
MyObject.prototype.constructor = MyObject;
MyObject.prototype.foo = function() {
  this.fire("foo");
};

var o = new MyObject();

o.addListener("foo", function(){
  alert("Foo just happened.");
});

o.call();