Programming ASP.NET AJAX

Chapter 3. Ajax

Ajax is the set of technologies upon which ASP.NET AJAX is built. And although ASP.NET AJAX does its best to hide the technical details of Ajax, to understand what is possible with ASP.NET AJAX and to create advanced applications that extend the framework for your own needs, you must have a detailed knowledge of Ajax.

The term “Ajax” was coined by Jesse James Garrett in early 2005 in his essay “A New Approach to Web Applications” (http://www.adaptivepath.com/publications/essays/archives/000385.php). However, only the term is new, not the technology itself. Although XML can be part of an Ajax application (but doesn’t need to be!), and some CSS may also be in the mix, the foundation of any Ajax-powered application is JavaScript.

In this chapter, you’ll create web pages that involve both client script in the browser and web server processing. Therefore, the examples in this chapter and the rest of the book will involve working with ASP.NET and with .aspx pages. We’ll also cover the three most important JavaScript technologies used to deliver Ajax behaviors to web apps. These technologies are outlined below:

XMLHttpRequest

The JavaScript object that takes care of making (asynchronous) HTTP calls

XMLDocument

The JavaScript object used to parse and access XML data

JavaScript Object Notation (JSON)

A data format that can be used instead of XML to exchange data between client and server without the burden of XML parsing

The XMLHttpRequest Object

The foundation of Ajax is the XMLHttpRequest ...