alert-page-leave.js

function goodbye(e) {
if(!e) e = window.event;
//e.cancelBubble supported by IE - this will kill the bubbling process.
e.cancelBubble = true;
e.returnValue = 'You sure you want to leave?';
//This is displayed on the dialog

//e.stopPropagation works in Firefox.
if (e.stopPropagation) {
e.stopPropagation();
e.preventDefault();
}
}
window.onbeforeunload=goodbye;