onbeforeunload problems

[Casey]

My client would like some of the larger forms on our project to alert the user if they attempt to navigate away before using the submit button.

Obviously I want to use a beforeunload event listener for this but I can't get it to fire.  In preview mode it fires an error because of the cross-source of the event listener, which is fine.  But in the live version it simply doesn't fire at all.  I'm using pretty simple syntax:

window.addEventListener("beforeunload", function(event) {
    event.returnValue = "Write something clever here..";
});

Is this something that Caspio suppresses?  Is there a workaround?  My client is pretty adamant about this functionality.

[Casey]

Ok, I solved it for myself.  It isn't working within the datapage footer but when I put the script on the footer of the webpage that I've embedded into the datapage it seems to work just fine