AJAX for Interactive Web Applications

Like DHTML, SPA and LAMP, Ajax is not a technology in itself, but a term that refers to the use of a group of technologies together.
Ajax, the acronym for Asynchronous JavaScript and XML, is a web development technique for creating interactive web applications. The idea is to make web pages more responsive by exchanging small amounts of data with the server in the back end, so that the entire web page does not have to be reloaded each time a user makes a change. This will increase the web page’s speed, interactivity and usability. Ajax applications effectively fill part of the niche first served by Java applets: extending the browser with lightweight mini-applications.
The Ajax technique uses a combination of:

• XHTML (or HTML) and CSS, for marking up and styling information.
• The DOM accessed with a client-side scripting language, especially ECMAScript implementations such as JavaScript and JScript, to dynamically display and interact with the information presented.
• XML is sometimes used as the format for transferring data between the client and server, though any format will work, including preformatted HTML and plain text. These files may be created dynamically by some form of server-side scripting.

On the downside, without smart preloading of data and proper handling of the XMLHttpRequest object, users might experience network latency or delay in the interface of the web application. Also, web applications that utilize Ajax may not fully use the browser’s back button. Users generally expect that clicking the back button will move their browser to the last page it loaded, and this might not be the case in Ajax applications as the dynamically modified page versus going back to a previous static page might not be obvious.