code: function(){
  		var onpresent = null;
  		Object.defineProperty(this, 'onpresent', {
  			get: function () {
  				return onpresent;
  			},
  			set: function(value){
  				if (typeof value == 'function' || typeof value == 'undefined' || value == null) {
  					onpresent = value;
  					if (onpresent) {
  						delegate.onpresent = function(delSession){
  							var session = new PresentationSession(delSession);
  							var evt = new PresentEvent('PresentEvent',{session: session})
  							onpresent.call(null,evt);
  						};
  					}
  					else {
  						delegate.onpresent = null;
  					}
  				};
  			}
  		});
  	}
docs: /*
  NavigatorPresentation: for details please refer to http://www.w3.org/2014/secondscreen/presentation-api/20140721/#navigatorpresentation