13.1 Overview of Ajax

Ajax refers to JavaScript and XML, technologies that are widely used for creating dynamic and asynchronous web content. While Ajax is not limited to JavaScript and XML technologies, more often than not they are used together by web applications. The focus of this tutorial is on using JavaScript based Ajax functionality in JavaServer Faces web applications.

JavaScript is a dynamic scripting language for web applications. It allows users to add enhanced functionality to user interfaces and allows web pages to interact with clients asynchronously. JavaScript runs mainly on the client side (as in a browser) and thereby reduces server access by clients.

When a JavaScript function sends an asynchronous request from the client to the server, the server sends back a response that is used to update the page's Document Object Model (DOM). This response is often in the format of an XML document. The term Ajax refers to this interaction between the client and server.

The server response need not be in XML only; it can also be in other formats, such as JSON (see Introduction to JSON and http://www.json.org/). This tutorial does not focus on the response formats.

Ajax enables asynchronous and partial updating of web applications. Such functionality allows for highly responsive web pages that are rendered in near real time. Ajax-based web applications can access server and process information and can also retrieve data without interfering with the display and rendering of the current web page on a client (such as a browser).

Some of the advantages of using Ajax are as follows:

• Form data validation in real time, eliminating the need to submit the form for verification

• Enhanced functionality for web pages, such as user name and password prompts

• Partial update of the web content, avoiding complete page reloads