Ajax: The Definitive Guide

Chapter 4. Foundations: Scripting XML and JSON

It’s time to switch gears and look at code for Ajax web applications. The most important part of an Ajax application is the connection between the client and the server. If this code is not solid and optimized, your application could suffer sluggish (or simply broken) behavior as a result.

You code the connection between the client and the server using JavaScript, and usually build the data format used to exchange information in XML. I say usually because a new format is on the rise and is fast becoming the new choice for web developers. This new format is JavaScript Object Notation (JSON).

In this chapter, we will explore how to use XML and JSON to transmit data. We will also discuss how the client and the server can parse or otherwise manipulate these formats. Of course, a discussion of this nature would be incomplete without some points on the differences among browser versions, and how to make cross-browser-compatible code.

XML

We will start with XML, as it is part of the original meaning of Ajax. This section will cover the basics of how Ajax works and what to do with the XML that is sent back and forth between the client and the server. First, driving the Ajax component of an Ajax web application is the XMLHttpRequest object. This object allows for asynchronous communication between the client and the server. In other words, the client can start communicating with the server, and instead of the client freezing up and becoming unusable ...