Chapter 2. Getting Started

In this chapter

	2.1 XMLHttpRequest Overview	page 16
	2.2 Cross-Browser XMLHttpRequest	page 21
	2.3 Sending Asynchronous Requests	page 23
	2.4 AJAX Without XMLHttpRequest	page 29
	2.5 Fallback Option 1: Sending a Request Using an IFrame	page 31
	2.6 Fallback Option 2: Sending a Request Using a Cookie	page 36
	2.7 Summary	page 39

The foundation that makes AJAX possible is the communication layer with the server. The most complete option for performing this communication is the JavaScript XMLHttpRequest object. If XMLHttpRequest is not suitable to you, hidden IFrames and cookies can also be used. We will examine both options later in this chapter.

This chapter introduces you to the XMLHttpRequest object, showing you how to work around its implementation differences between browsers. After that, we make some actual page requests, both in a synchronous fashion and in an asynchronous fashion. This chapter finishes with some various fallback approaches that can be used if a browser doesn't support XMLHttpRequest, including how to use IFrames and cookies as your communication channel.