16.1. Introduction

Despite the tremendous technological growth of the Internet over the past decade, the usability of web applications has lagged behind that of desktop applications. Rich Internet Applications (RIAs) are web applications that approximate the look, feel and usability of desktop applications. Two key attributes of RIAs are performance and a rich GUI.

RIA performance comes from Ajax (Asynchronous JavaScript and XML), which uses client-side scripting to make web applications more responsive. Ajax applications separate client-side user interaction and server communication and run them in parallel, reducing the delays of server-side processing normally experienced by the user.

There are many ways to implement Ajax functionality. “Raw” Ajax uses JavaScript to send asynchronous requests to the server, then updates the page using the DOM. “Raw” Ajax is best suited for creating small Ajax components that asynchronously update a section of the page. However, when writing “raw” Ajax you need to deal directly with cross-browser portability issues, making it impractical for developing large-scale applications. These portability issues are hidden by Ajax toolkits, such as jQuery, ASP.NET Ajax and JSF’s Ajax capabilities, which provide powerful ready-to-use controls and functions that enrich web applications and simplify JavaScript coding by making it cross-browser compatible.