How can I override the OnBeforeUnload dialog and replace it with my own?

Question

I need to warn users about unsaved changes before they leave a page (a pretty common problem).

window.onbeforeunload=handler

This works bu

Answer 1

What worked for me, using jQuery and tested in IE8, Chrome and Firefox, is:

$(window).bind("beforeunload",function(event) {
    if(hasChanged) return "You have unsaved changes";
});

It is important not to return anything if no prompt is required as there are differences between IE and other browser behaviours here.