The keystone of AJAX is the XMLHttpRequest object.

Different browsers use different methods to create the XMLHttpRequest object.

Internet Explorer uses an ActiveXObject, while other browsers uses the built-in JavaScript object called XMLHttpRequest.

To create this object, and deal with different browsers, we are going to use a "try and catch" statement. You can read more about the try and catch statement in our JavaScript tutorial.

I’m going to tell you new piece of Ajax information.
Ok what’s Ajax? - Asynchronous JavaScript + XML, new great technology which closely related with conception of web2. If you saw amazing products of Google(gmail, google maps) you could notice that this applications is very  similar with usual desktop applications it’s Ajax. The main point of using it is the great usability, speed of interactions and a big traffic’s economy. And your applications don’t need postbacks!!!
But it has one disadvantage you need to write a lot of client side code so you should be careful to manage with it.

Ok, so my little del.icio.us app (click link to read about how I added Ajax functionality to a simple Rails app) is pretty cool, but it was missing one big thing. When the user clicks the "Get Results" link she has no idea that the page is communicating with the server. While the communication doesn't go on forever, an impatient user might click the link multiple times.

So, we need a way of letting the user know that something is happening and that they ought to wait a bit. Today, the standard seems to be an animated spinning icon:

After a slow start (following the announcement of the XHTML (ajax) Chat) things got finally busy. I had so many requests that I have decided to offer the complete sources for download. As everything on plasticshore I am releasing it under the always same creative commons license.

Please be mindful that I am not a developer but a designer. My code might not live up to any standards and commenting is something I have only learned recently :)
This is not a one click install solution for the casual surfer but something that can be set up and run by anybody with a good understanding of PHP and mySQL.

I find a lot of this AJAX stuff a bit of a hype. Lots of people have been using similar things long before it became “AJAX”. And it really isn’t as complicated as a lot of people make it out to be. Here is a simple example from one of my apps. First the Javascript: