Prompt User before browser close?

Question

We have an administrative portal that our teachers constantly forget to download their latest PDF instructions before logging out and/or closing the browser window. I have l

Answer 1

Update 2017

All modern browsers do not support custom messages any longer.

window.onbeforeunload = function(evt) {
   return true;
}

This one for closing the tab:

window.onbeforeunload = function(evt) {
    var message = 'Did you remember to download your form?';
    if (typeof evt == 'undefined') {
        evt = window.event;
    }
    if (evt) {
        evt.returnValue = message;
    }

    return message;
}

and use onClick event for logout button:

onClick="return confirm('Did you remember to download your form?');"