notice before reload js

1<script>
2  // Warning before leaving the page (back button, or outgoinglink)
3window.onbeforeunload = function() {   
4  return "Do you really want to leave our brilliant application?";   
5  //if we return nothing here (just calling return;) then there will be no pop-up question at all   
6  //return;
7};
8</script>