Professional LAMP: Linux®, Apache, MySQL®, and PHP5 Web Development

Chapter 11. AJAX

Typical web applications interact with the user via forms. The server sends the client a form, the user enters responses, and the form is submitted back to the server for processing. Once the form is processed, the server responds with a new complete page, the composition of which is often dependent upon the user's last form submission. In each interaction with the user, an entirely new page is required. Such applications must use bandwidth, transferring constant page elements (site navigation, for example) with each page request, even though these elements were sent to the client in previous responses. Further, such applications are slower than desktop applications, because the web application is unresponsive while the results of one interaction are being processed and until the new page loads.

AJAX (Asynchronous JavaScript and XML) refers to a group of technologies that allows for the creation of fat-client web applications, where the responsibility for a relatively large portion of the application processing is given to the client. Specifically, AJAX applications often use XHTML and CSS for semantic markup and presentation, XML to format data that will be exchanged between client and server, and JavaScript to communicate with the server and manipulate the Document Object Model (DOM). When using AJAX, communication between the client and the server can be limited to data only, as the client has the functionality necessary to handle presentation and user interaction. ...