Professional Ajax, 2nd Edition

3.1. Communication Control Patterns

You already know, from Chapter 2, how to communicate with the server from JavaScript. The real question is: What is the best way to initiate and continue to make requests back to the server? In some cases, it may be best to preload information from the server so that it is available immediately upon some user action. In other cases, you may want to send data to, or receive data from, the server in varying intervals. Perhaps everything shouldn't be downloaded at once, and instead should be downloaded in a particular sequence. Ajax affords you fine granularity in controlling the communication between client and server to achieve your desired behavior.

3.1.1. Predictive Fetch

In a traditional web solution, the application has no idea what is to come next. A page is presented with any number of links, each one leading to a different part of the site. This may be termed "fetch on demand," where the user, through his or her actions, tells the server exactly what data should be retrieved. While this paradigm has defined the Web since its inception, it has the unfortunate side effect of forcing the start-and-stop model of user interaction upon the user. With the help of Ajax, however, this is beginning to change.

The Predictive Fetch pattern is a relatively simple idea that can be somewhat difficult to implement: the Ajax application guesses what the user is going to do next and retrieves the appropriate data. In a perfect world, it would be wonderful ...