Can beforeunload/unload be used to send XmlHttpRequests reliably

Question

recently, I had the urgent requirement to give my server a notice, that a specific page of my webapp is about to get closed. \"Easy peasy\" I thought, beforeu

Answer 1

Take a look at navigator.sendBeacon(), which allows you to reliably send data to a server even when the page is unloading. It's currently in a draft specification and supported by Firefox 31, Chrome 39 (behind a flag from 37), behind a flag in Opera 24.

You could "sort of" polyfill it using something like the following:

navigator.sendBeacon = navigator.sendBeacon || function (url, data) {
    var xhr = new XMLHttpRequest();

    // Need to send synchronously to have the best chance of data getting
    // through to the server
    xhr.open('POST', url, false);
    xhr.send(data);
};

Further reading:

• HTML5 Rocks article