window.onbeforeunload = function (eventargs)
{
 for (i in DirtyPanelExtender_dirtypanels)
 {
  var panel = DirtyPanelExtender_dirtypanels[i];
  if (panel.isDirty())
  {
   if(! eventargs) eventargs = window.event;
   eventargs.returnValue = panel.get_OnLeaveMessage();
   break;
  }
 }
}