Handle closing event on a mac

/*
 * How to gracefully handle the closing event on a mac
 */
napp.openedWindows[0].addEventListener(Event.CLOSING,
   function(e:Event):void {
     var w:NativeWindow = e.currentTarget as NativeWindow;
     if(w.active) {
       e.preventDefault();
       napp.openedWindows[0].visible = false;
     } else {
       napp.exit();
     }
   });