onBeforeUnload handler says null in IE

Question

my web-app has this:

$(window).bind(\'beforeunload\', function() {
    if(unSavedChanges == true)
    {
        return \'You have unsaved changes\';
    }
           


        

Answer 1

I use normal javascript for this and works fine

function setConfirmUnload(on) {
     window.onbeforeunload = (on) ? unloadMessage : null;
}

function unloadMessage() {
     return 'Please stay on the page';
}

Answer 2

Remove the return null line and it should be fine (in Javascript null and undefined are different things).

By the way, MDN says that for maximum compatibility you should be accepting an event parameter and setting event.returnValue as well.