Guide to Using XMLHttpRequest (with Baby Steps) from WebPasties

“Although the XMLHttpRequest object might sound complex and different from any other JavaScript object you have ever used, it really isn’t. A good way to think of the XMLHttpRequest object is as you would think of the JavaScript Image object. As we know, with the Image object you can dynamically specify a new URL for the image source without reloading the page. Similarly with the XMLHttpRequest object, you can dynamically specify a URL to get some server data without reloading the page.”