JavaScript is a simple programming language from Netscape that can be embedded in your HTML Web pages. It allows you to control the behavior of the Web browser, add dynamically created text to your Web pages, interact with the user through HTML forms (withoutCGI scripts), and, in version 3.0 of Netscape Navigator, even control and interact with Java applets and Navigator plugins. JavaScript is not an alternative to Java, but an ideal partner. The two languages have separate but very complementary features. Since JavaScript is a simple language that can be embedded directly into a Web page, without need for compilation, it is accessible to more Web page authors, and may actually have a larger short-term impact on the Web and on Internet computing than Java itself. This book is a definitive guide for JavaScript. The first eight chapters document the core JavaScript language, and the next six describe how JavaScript works on the client-side to interact with the Web browser and with the Web page. These chapters are followed by acompletereference section that documents every object, property, method, event handler, function, and constructor used by client-side JavaScript. In a separate reference section, you will find the interaction between JavaScript and HTML documented -- mainly aspects of HTML that relate to JavaScript. A forthcoming edition of this book will cover the use of JavaScript on Web servers, as well as the object, properties, and methods of server-side JavaScript. This book documents the version of JavaScript shipped with Navigator 2.0, 2.0.1, and 2.0.2, and also the much-changed version of JavaScript shipped with beta versions of Navigator 3.0. The 3.0 information is current as of the 3.0b4 release. JavaScript is also supported in Microsoft Internet Explorer 3.0, and this book discusses JavaScript support in Beta 1 of MSIE. A notable feature of these versions of JavaScript is the frustrating number of bugs that still exist. The book contains a long list of known bugs and is careful to document commonly encountered bugs on the reference pages of the JavaScript objects. Why is this book in "Beta"? We printed this book in a "beta" edition because JavaScript is rapidly evolving. Within Netscape, the version of JavaScript that will be in Navigator 3.0 is being called "JavaScript 1.0." This is an implicit admission that JavaScript as implemented in Navigator 2.0 was still a beta version of the language. Despite JavaScript's beta status, a tremendous number of people are using it and need quality documentation for it. At the same time, however, we realize there have been a lot of changes to JavaScript since Navigator 2.0 was released. As this book is being written, Navigator is at the 3.0b4 stage, and we are beginning to hear about the new features that will be available in the 3.0b5 release. It seems, in fact, that JavaScript is changing faster at this point than at any other time in its development. Since we intend for this book to be adefinitiveguide for the Navigator 2.0andNavigator 3.0 versions of JavaScript, we are not ready to release the first edition of the book until Navigator 3.0 is released in final form. Since beta software has become the norm in these days of rapid innovation on the Internet, we realized that there was no reason we couldn't apply the same model to our high-priority books. By printing this beta edition we can get timely information out to our customers without giving the impression that the book is in its final form. In order to get the beta version of the book out quickly (which is the whole point!) we have not put it through all the quality-control checks that O'Reilly books usually go through. So forgive us if you find typos or awkward prose. As a reader of this beta edition of the book, you can help us to improve the final edition by serving as a beta-tester. If you find errors, inaccuracies, or typos anywhere in the book, or explanations that are not clear, or statements that are misleading, please let us know about them by sending email tobookquestions@ora.com.