Introduction
XMLHttpRequest is a JavaScript function that allows the core dynamic data part of AJAX (Asynchronous JavaScript And XML) to work. It lets JavaScript running in a web browser call a URL on the same server and receive data back again to process. Either normal HTML, XML or any format such as JSON can be returned and the JavaScript can do what it likes with it. This lets the page update itself or submit a form without making the whole page refresh which typically gives the user a much better experience. Obvious examples are a news website with up-to-date news ‘ticker’-style headlines or live sports commentary, Viewing more comments in YouTube, Search engine pop-up suggestions as you type, and so on.
