JavaScript: The Missing Manual

Chapter 11. Introducing Ajax

JavaScript is great, but it can’t do everything. If you want to display information from a database, dash off an email with results from a form, or just download additional HTML, you need to communicate with a Web server. For these tasks, you usually need to load a new Web page. For example, when you search a database for information, you usually leave the search page and go to another page of results.

Of course, waiting for new pages to load takes time. And, if you think about it, the concept of a page disappearing and then reappearing is pretty strange in general. Imagine if you were using Microsoft Word and every time you opened a new file the program’s menus, panels, and windows suddenly disappeared and then reappeared when the new file opened. Sites like Flickr, Twitter, Google Maps, and Gmail are blurring the line between Web sites and desktop computer programs. If anything, people want Web sites to feel faster and more responsive, like their desktop programs. The technology that makes this new generation of Web applications possible is a programming technology called Ajax.

Ajax lets a Web page ask for and receive a response from a Web server and then update itself without ever having to load a new Web page. The result is a Web site that feels more responsive. When you visit Google Maps, for example (see Figure 11-1), you can zoom into the map; move north, south, east, or west; and even grab the map and drag it around. All of these actions happen ...