window before refresh event code example

Example: notice before reload js

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