Once listed in the "nice to have" sections of job postings, these days the knowledge of JavaScript is a deciding factor when it comes to hiring web developers. And rightly so. Where in the past we used to have the occasional few lines of JavaScript embedded in a web page, now we have advanced libraries and extensible architectures, powering the "fat-client", AJAX-type rich internet applications. JavaScript is the language of the browser, but it's also heavily employed in many other environments: server-side programming, desktop applications, application extensions and widgets. It's a pretty good deal: you learn one language and then code all kinds of different applications. While this book has one chapter specifically dedicated to the web browser environment including DOM, events, and AJAX tutorials, the rest is applicable to all the other environments too. This book treats JavaScript as a serious object-oriented language, showing you how to build robust, maintainable, and powerful libraries and applications. Along the way, we cover many of the recent innovations such as AJAX, JSON, and interesting design and coding patterns. After reading this book, you'll be prepared to ace your JavaScript job interview and even impress with some bits that the interviewer maybe didn't know. You should read this book if you want to be able to take your JavaScript skills to a new level of sophistication.