Book excerpt: Professional Ajax 2nd Edition provides a developer-level tutorial of Ajax techniques, patterns, and use cases. The book begins by exploring the roots of Ajax, covering how the evolution of the web and new technologies directly led to the development of Ajax techniques. A detailed discussion of how frames, JavaScript, cookies, XML, and XMLHttp requests (XHR) related to Ajax is included. After this introduction, the book moves on to cover the implementation of specific Ajax techniques. Request brokers such as hidden frames, dynamic iframes, and XHR are compared and contrasted, explaining when one method should be used over another. To make this discussion clearer, a brief overview of HTTP requests and responses is included. Once a basic understanding of the various request types is discussed, the book moves on to provide in-depth examples of how and when to use Ajax in a web site or web application. Different data transmission formats, including plain text, HTML, XML, and JSON are discussed for their advantages and disadvantages. Also included is a discussion on web services and how they may be used to perform Ajax techniques. Next, more complex topics are covered. A chapter introducing a request management framework explores how to manage all of the requests inside of an Ajax application. Ajax debugging techniques are also discussed. Professional Ajax 2nd edition is written for Web application developers looking to enhance the usability of their web sites and web applications and intermediate JavaScript developers looking to further understand the language. Readers should have familiarity with XML, XSLT, Web Services, PHP or C#, HTML, CSS. Professional Ajax 2nd edition adds nearly 200 pages of new and expanded coverage compared to the first edition.