confirm() on [removed]

Question

I want to show a confirmation dialog if the user wants to leave the page with unsaved form data. What I have is:

window.onbeforeunload = function() {
    if          


        

Answer 1

Although window.onbeforeunload works, it's considered bad practice. It's better to use something like the following:

if (typeof window.addEventListener === 'undefined') {
    window.addEventListener = function(e, callback) {
        return window.attachEvent('on' + e, callback);
    }
}

window.addEventListener('beforeunload', function() {
    return 'Dialog Text Here';
});

First we check if window.addEventListener exists, which it does not in IE, else we polyfill it, and then we attach the event.