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Reviewer: Arthur Gittleman

Asynchronous Javascript and Extensible Markup Language (XML) (Ajax) techniques are not new, but they are newly practical in building more responsive Web clients that do not require full page refreshes to reflect changes in a local area of the page. This book is an excellent introduction that opts for simplicity in its examples, avoiding extraneous details, such as database configuration, that would clutter the code with complicated details not relevant to the theme of the book. Ajax is used to build more responsive Web clients. The client uses Javascript, and can work with any server-side language, such as Java, PHP: hypertext preprocessor (PHP), or Perl. Examples here use Java on the server. Code downloadable from the publisher's site is very easy to use with Tomcat. For each chapter, one only needs to copy a Web application archive (WAR) file to a Tomcat folder to be able to run all of that chapter's examples. Although clearly written, with careful explanations, the book does assume some prior exposure to Javascript and Web application development. "The Introduction to Ajax" gives a cogent history of Web applications that shows why Ajax has recently become practical. In addition to identifying the advantages of Ajax, the authors carefully point out some changes in the user's experience about which developers should be aware. They suggest starting by trying Ajax in places where it can be most useful, including validation. Illustrations of several sites show the usefulness of Ajax, including Netflix, which uses Ajax to display a tooltip when a customer uses the mouse to hover over the graphic for a movie. "Using the XMLHttpRequest Object" presents the core of Ajax, the creation of an XMLHttpRequest object, the sending of an asynchronous request, and the provision of a callback method that executes when the response arrives. The code for the first example forms the core of all later examples, so the pattern is easy to discern. The examples in chapter 3 cover processing the server's response, and sending data from the client to the basic core. The authors have done well to keep things simple, but may have overdone it in the real estate listing example, in which the user's price selections have no effect. Chapter 4 implements some basic Ajax techniques, including performing validation, reading response headers, dynamically loading list boxes, creating an auto-refreshing page, displaying a progress bar, creating tooltips, dynamically updating a Web page, accessing Web services, and providing auto-complete functionality. The examples are all easy to follow. The remaining chapters provide Ajax support. Chapter 5 is a developer's toolbox. Chapter 6 covers unit testing with JsUnit. Chapter 7 addresses Javascript debugging, while the final chapter covers patterns and the Taconite framework for Ajax, developed by the authors. Two appendices discuss developing cross-browser Javascript, and briefly describe other Ajax frameworks. This book is a fine introduction for almost anyone with the suggested background. Some Web gurus may prefer to grapple with a longer tome, with more complex examples and more coverage of advanced topics, but most will prefer the smooth sailing found here; they can learn to navigate the deeper waters later if desired. Online Computing Reviews Service