What do Yahoo! Maps, Google Maps, Yahoo! Mail, My Yahoo!, Gmail, Digg, YouTube and a plethora of other popular "Web 2.0" applications have in common? They all offer rich and responsive user interfaces, heavily employing code written in the JavaScript language. JavaScript started with simple one-liners embedded in HTML, but is now used in much more sophisticated ways. Developers leverage the object-oriented nature of the language to build scalable code architectures made up of reusable pieces. JavaScript provides behavior, the third pillar in today's paradigm that sees web pages as consisting of three clearly distinguishable parts: content (HTML), presentation (CSS), and behavior (JavaScript).

JavaScript programs run inside a host environment. The web browser is the most common environment, but it is not the only one. Using JavaScript, you can create all kinds of widgets, application extensions, and other pieces of software. Learning JavaScript is a pretty good deal: you learn one language and can then code all kinds of different applications.

This book is about JavaScript and focuses on its object-oriented nature. The book starts from zero, and does not assume any prior programming knowledge. Although there is one chapter dedicated to the web browser environment, the rest of the book is about JavaScript in general, so is applicable to all environments.

Let's start with the first chapter, which gives you an overview of the story behind JavaScript. It also introduces the basic concepts you'll encounter in discussions on object-oriented programming.