custom classes with jeash

Hi

I'm trying to extend Sprite class with some public properties and methods, and then call them from Main class (NME ofcourse):
/////////////////////////////////////////////
var item = new FilmstripItem("abc");
stage.addChild(item);
item.addEventListener(MouseEvent.CLICK, item_click);
...
private function item_click(e:MouseEvent):Void {
var a:FilmstripItem;
a = cast e.target;
trace(e.target.url);
}
/////////////////////////////////////////////
and the custom FilmstripItem class:
/////////////////////////////////////////////
import nme.display.Sprite;

class FilmstripItem extends Sprite{

public var url : String;

public function new(url:String) {
this.url = url;
super();
}
}
/////////////////////////////////////////////
it works fine when I build it for flash output, but, in html5 the value is null. I also tried with the method inside of FilmstripItem class, but it gives me error (the popup comes out with script error message boot_closure@67)

Is it possible to do it?

thanks