Intercept page exit event

Question

When editing a page within my system, a user might decide to navigate to another website and in doing so could lose all the edits they have not saved.

I would like to intercept any attempt to go to another page and prompt the user to be sure they want this to happen since they could potentially lose their current work.

Gmail does this in a very similar way. For example, compose a new email, start typing into the message body and enter a new location in the address bar (say twitter.com or something). It will prompt like so:

Ideas how to replicate this? I'm targeting IE8, but would like to be compatible with FF & Chrome also.

Answer 1

See this article. The feature you are looking for is the onbeforeunload

sample code:

  <script language="JavaScript">
  window.onbeforeunload = confirmExit;
  function confirmExit()
  {
    return "You have attempted to leave this page.  If you have made any changes to the fields without clicking the Save button, your changes will be lost.  Are you sure you want to exit this page?";
  }
</script>

Answer 2

Similar to Ghommey's answer, but this also supports old versions of IE and Firefox.

window.onbeforeunload = function (e) {
  var message = "Your confirmation message goes here.",
  e = e || window.event;
  // For IE and Firefox
  if (e) {
    e.returnValue = message;
  }

  // For Safari
  return message;
};