code: function(type, eventInitDict){
      this.type = type;
      var available = eventInitDict && eventInitDict.available == true;
      Object.defineProperty(this, "available", {
        get: function () {
          return available;
        }
      });
  }
docs: WebIDL: AvailableChangeEvent
  
  [Constructor(DOMString type, optional AvailableChangeEventInit eventInitDict)]
  interface AvailableChangeEvent : Event {
  readonly attribute boolean available;
  };
  
  dictionary AvailableChangeEventInit : EventInit {
  boolean available;
  };
  
  http://www.w3.org/2014/secondscreen/presentation-api/20140721/#AvailableChangeEvent_interface