easeljs cannot dispatch event - easeljs

Question

I want to dispatch my event,but it doesn't work. this is my code and I've deleted some irrelevant parts .
(function(window){
function HeroSelectView(){
this.initialize();
}
createjs.EventDispatcher.initialize(HeroSelectView.prototype);
HeroSelectView.prototype = new createjs.Container();
var selectedName;
HeroSelectView.prototype.Container_initialize=HeroSelectView.prototype.initialize;
HeroSelectView.prototype.initialize=function(){
this.Container_initialize();
this.initView();
}
HeroSelectView.prototype.initView = function(){
for (var i = 0; i < heroArray.length; i++) {
heroArray[i].x=100+40*i;
heroArray[i].y=200;
this.addChild(heroArray[i]);
heroArray[i].addEventListener("click",onSelectHero);
};
}
function onSelectHero(event){
selectedName=event.target.name;
var myevent = {
type: "selectedEvent",
param: selectedName
};
//var myevent=new createjs.Event("selectedEvent"); //createjs 0.7 doesnot work either.
this.dispatchEvent(myevent);
}
window.HeroSelectView=HeroSelectView;
}(window))
in the onSelectedHero, at first I tried it with createjs-0.61. you can see the "myevent" .But there is an error " TypeError: Argument 1 of EventTarget.dispatchEvent is not an object.". Then I tried it with version 0.7, but still got the same error. How can I fix this?
Thanks