Are you sure you want to navigate away from this page? #JavaScript warning

window.onbeforeunload = function (e) {
                return "You have made unsaved changes. Are you sure you want to navigate away from this page?";
            };

Javascript

//http://stackoverflow.com/questions/1119289/how-to-show-the-are-you-sure-you-want-to-navigate-away-from-this-page-when-ch
//To turn it on:

window.onbeforeunload = function (e) {
                return "You have made unsaved changes. Are you sure you want to navigate away from this page?";
            };

//To turn it off:

// window.onbeforeunload = null;

//Bear in mind that this isn't a normal event - you can't bind to it in the standard way.
//To check for values? That depends on your validation framework.
//In jQuery this could be something like (very basic example):

$('input').change(function() {
    if( $(this).val() != "" )
        window.onbeforeunload = "Are you sure you want to leave?";
});