Ext JS, a cross-browser JavaScript library for building Rich Internet Applications (RIA), has emerged from the mix of JavaScript frameworks, libraries and object-oriented development techniques as a one of the clear leaders. Ext JS combines an extensive library of super-high-quality widgets, an intuitive, extensible component model, and an easy-to-use API to create a full, rock-solid platform for JavaScript-based web apps. Ext JS has been adopted by such household names as Adobe, Aetna, Amazon.com, Best Buy Hallmark, Panasonic, Pixar Animation Studios, Siemens, Sony, and Visa. "Ext JS in Action" teaches the reader about Ext from the ground up. By following the common design patterns demonstrated in the Ext source and in many commercial applications, the book teaches you to achieve the same results you see in world-class commercial JavaScript applications. This book will guide you through the Ext component model and layouts. You'll learn how core components, such as the Container class, serve as building blocks for building complex user interfaces. The book fully covers Ext utility classes, AJAX, Observable (the Ext events model), DOM helpers and Function Helpers and illustrates how use of JavaScript Object Notation (JSON), a powerful and lightweight data format, can allow your application to efficiently communicate over the network to the web server. Finally, you'll build on this foundation to customize or extend Ext widgets. "Ext JS in Action" assumes that you have a solid foundation in JavaScript, but requires no previous exposure to Ext JS.