Handle "Your changes will be lost" prompt when navigating away from a changed page.

confirm_discard.js

// To activate this, add the class "confirm_discard" to your form. If
// you change any value on the form, it will set the onbeforeunload.
// When you send the submit event (AJAX or normal GET / POST), it
// clears it. Since it uses delegate, there's no need to run
// additional setup code after an ajax call has loaded a form on the
// page.

// This won't interfere with any other custom beforeunload event
// handlers you may have.
// This works with multiple forms on a page as well.

// To force form to be marked 'dirty', you can $('form').data('data-changed',true);
// To force clear the changed flag, you can $('form').data('data-changed',false);
// To test if a form is dirty, you can call $('form').data('data-changed).

$('body').delegate('form.confirm_discard input, form.confirm_discard select, form.confirm_discard textarea','change',function(){
    $(this).closest('form.confirm_discard').data('data-changed', true);
});
$('body').delegate('form.confirm_discard','submit',function(){
    $(this).closest('form.confirm_discard').data('data-changed', false);
});
$(window).bind('beforeunload',function(){
    var foundChange = false;
    $('form.confirm_discard').each(function(){
        if ($(this).data('data-changed')){
            foundChange = true;
        }
    });
    if (foundChange){
        return "If you proceed, your changes will be lost";
    }
});