Use of onbeforeunload for prevent closing page

onbeforeunload.js

<script>
  window.onbeforeunload = function (event) {
    var message = 'Important: Please click on \'Save\' button to leave this page.';
  
    if (typeof event == 'undefined') {
      event = window.event;
    }
  
    if (event) {
    event.returnValue = message;
    }
  
    return message;
  };

  $(function () {
    $(".safe").click(function () {
      window.onbeforeunload = null;
    });
  });
</script>