AJAX Basics

AJAX simply means Asynchronous JavaScript and XML. AJAX is not a language but a way of using existing standards in different or new way. With AJAX we can update part of a webpage part from server data without having to reload whole page. For example if a webpage is displaying number of users actively using website. Here we can use AJAX to update active user number periodically without reloading whole page again. This means we can update web page asynchronously by exchanging data from server using AJAX.

In short AJAX using internet standards interacts between client (browser) and web server. It uses combination

1. XMLHttpRequest object (to exchange data asynchronously with server). * 
2. JavaScript/DOM (this is display/update specific webpage part)
3. CSS (This is to apply style).
4. XML (Most often data is exchanged in XML format)

First question that strikes our mind is what we need to know before we start studying/exploring AJAX?

We should be aware of HTML / XHTML, CSS, JavaScript / DOM and basic XML. There are various resources available where we can brush-up the fundamentals of these.

Next question is how AJAX works?

Browser	Internet	Server	Internet	Browser
When page event occurs 1) XMLHttpRequest object is create 2) Then HTTPRequest is send	==>	1) HTTPRequest is processed 2) Appropriate response with date is send back	==>	1) JavaScript process response 2) Updates appropriate page content

For me this is sufficient as basics of AJAX.