What is AJAX ?

AJAX (short for asynchronous javascript and XML) is not a new programming language, but a new way  to use existing standards.AJAX is the art of exchanging data with a server, and updating parts of a web page - without reloading the whole page.AJAX is a technique for creating fast and dynamic web pages.

AJAX allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.Classic web pages, (which do not use AJAX) must reload the entire page if the content should change.

·         Ajax uses XHTML for content, CSS for presentation, along with Document Object Model  and   JavaScript for dynamic content display.

·         Conventional web applications transmit information to and from the sever using synchronous   requests. It means you fill out a form, hit submit, and get directed to a new page with new  information from the server.

·         With AJAX, when you hit submit, JavaScript will make a request to the server, interpret the results,    and update the current screen. In the purest sense, the user would never know that anything was  even   transmitted to the server.

·         XML is commonly used as the format for receiving server data, although any format, including  plain   text, can be used.

·         AJAX is a web browser technology independent of web server software.

·          A user can continue to use the application while the client program requests information from the  server in the background.

·          Intuitive and natural user interaction. Clicking is not required, mouse movement is a sufficient  event   trigger.

·          Data-driven as opposed to page-driven.

Technologies

The term Ajax has come to represent a broad group of Web technologies that can be used to implement a Web application that communicates with a server in the background, without interfering with the current state of the page.

Since then, however, there have been a number of developments in the technologies used in an Ajax application, and the definition of the term Ajax. XML is not required for data interchange and, therefore, XSLT is not required for the manipulation of data. JavaScript Object Notation (JSON) is often used as an alternative format for data interchange, although other formats such as preformatted HTML or plain text can also be used.

Asynchronous HTML and HTTP (AHAH) involves using XMLHTTPRequest to retrieve (X)HTML fragments, which are then inserted directly into the Web page.

Advantages of AJAX

• Reduce the traffic travels between the client and the server.
• Response time is faster so increases performance and speed.
• You can use JSON (JavaScript Object Notation) which is alternative to XML.JSON is key value pair and works like an array.
• You can use Firefox browser with an add-on called as Firebug to debug all   Ajax calls.
• Ready Open source JavaScript libraries available for use – JQuery, Prototype,   Scriptaculous, etc..
• AJAX communicates over HTTP Protocol.