Technologies That Make Up AJAX

AJAX is a general umbrella term. AJAX itself stands for Asynchronous JavaScript And XML. The term was coined by Jesse James Garret of Adaptive Path in an essay published in February 2005 (http:// www.adaptivepath.com/publications/essays/archives/000385.php) and was quickly accepted by the development community.

Based on this general umbrella term, take a look at the specific items that make up AJAX:

• XMLHttpRequest — XMLHttpRequest allows the browser to communicate to a back-end server. This object allows for the browser to talk to the server without requiring a postback of the entire web page. With Internet Explorer 5 and 6, this capability is provided by the MSXML ActiveX component. With the Mozilla Firefox, IE 7, and other web browsers, this capability is provided by an object literally called XmlHttpRequest. The XmlHttpRequest object is modeled after the MSXML component and defined by the XMLHttpRequest standard from the W3C. The ASP.NET 2.0 AJAX client-side JavaScript libraries hide the differences between the various browsers.
• JavaScript—JavaScript provides the capability to communicate with the back-end server. The version of JavaScript must be version 1.5 or later. Though JavaScript is not specifically required, it is needed from the standpoint that JavaScript is the only client-side scripting environment supported across the major modern web browsers. There are other client script languages; however, these are not supported across all browsers.
• DHTML/DOM support—The browser must support the ability to dynamically update form elements, and the ability to do this in a standard way comes through the support for the Document Object Model (DOM). By supporting the DOM, it becomes easy for developers to write a single piece of code that targets multiple browsers.
•  Data transport with XML or JSON — Using XML allows for the ability to communicate with the web server in a standard mechanism. The default data format with ASP.NET AJAX is JSON.