Developing Large Web Applications

Chapter 8. Large-Scale Ajax

Ajax (Asynchronous JavaScript and XML) is not so much a new technology as a set of existing technologies used together in a new way, bound together by a mechanism that lets you communicate between the browser and server without reloading the entire page. In its most fundamental form, Ajax requires that you understand only one new piece: the XMLHttpRequest object in JavaScript (or its equivalent depending on the browser). This is the object that allows you to make a connection back to the originating server to request additional data. Once you receive the data, you can use it to adjust only the portion of the page that you need to update.

Although the object’s name and the term “Ajax” itself imply that XML is the only format for exchanging data, there are others. JSON is especially good because it lets you pass a string of JavaScript on which you call json_parse (which you can download from http://json.org/json_parse.js), to yield a JavaScript object.

Certain practices simplify working with Ajax. Usually, it’s helpful to load a library that abstracts the XMLHttpRequest object. Fortunately, there are several libraries that help with this. In addition, within the browser, the MVC design pattern is a good model for maintaining a clear separation between data changes and updates to a presentation. On the server, the same principles discussed in Chapter 6 for managing data for complete pages can also provide a good structure for data in Ajax requests. These ideas ...