onbeforeunload support for js navigation (via hashchange, such as backbone.history, etc)

onbeforeunload.js

var cancelNavigate;
$(window).on("hashchange", function(ev) {
  if(cancelNavigate) {
    cancelNavigate = false;
    return false;
  }
  if(window.onbeforeunload) {
    var ok = confirm(window.onbeforeunload());
    if(ok) {
      window.onbeforeunload = null;
      return;
    } else {
      cancelNavigate = true;
      window.location.href = ev.originalEvent.oldURL;
      return false;
    }
  }
});

It does not work on IE, because it does not have the oldURL property.. for these case, you have to manually track the previous href.

Thanks for this

This doesn't cover cases where window.onbeforeunload() is defined but returns null, meaning it should not prevent navigation. I would change line 8 to:

var msg = window.onbeforeunload();
if (!msg) return;
var ok = confirm(msg);
if (ok) {