JavaScript is a powerful scripting language that can be embedded directly in HTML. It allows you to create dynamic, interactive Web-based applications that run completely within a Web browser; you don't have to do any server-side programming, like writing CGI scripts.

JavaScript is a simpler language than Java. It can be embedded directly in Web pages without compilation, so it is more flexible and easier to use for simple tasks like animation. However, although you can write reasonably robust and complete Web applications using JavaScript alone, JavaScript is not a substitute for Java. In fact, JavaScript is a good client-side complement to Java; using the two together allows you to create more complex applications than are possible with JavaScript alone.

JavaScript: The Definitive Guide provides a thorough description of the core JavaScript language and its client-side framework, complete with sophisticated examples that show you how to handle common tasks, like validating form data and working with cookies. The book also contains a definitive, in-depth reference section that covers every core and client-side JavaScript function, object, method, property, constructor, and event handler. This book is an indispensable reference for all JavaScript programmers, regardless of experience level.

This third edition of JavaScript: The Definitive Guide describes the latest version of the language, JavaScript 1.2, as supported by Netscape Navigator 4 and Internet Explorer 4. The book also covers JavaScript 1.1, which is the first industry-standard version known as ECMAScript. The new features of JavaScript 1.2, which are likely to be embodied in a later ECMAScript standard release, are clearly indicated, so that you can use them as appropriate in your scripts.