What's New in the Fourth Edition

This edition of JavaScript: The Definitive Guide has been thoroughly updated in light of the changes I just described. Major new features include complete coverage of JavaScript 1.5 and the third edition of the ECMA-262 standard on which it is based, and complete coverage of the Level 2 DOM standard.

Throughout the book, the focus has shifted from documenting particular JavaScript and browser implementations ( JavaScript 1.2, Netscape 4, Internet Explorer 5, etc.) to documenting the standards upon which those implementations are (or ought to be) based. Because of the proliferation of implementations, it is no longer practical for any one book to attempt to document -- or for any one developer to attempt to understand -- every feature, proprietary extension, quirk, and bug of every implementation. Focusing on the specifications instead of the implementations makes this book easier to use and, if you take the same approach, will make your JavaScript code more portable and maintainable. You'll particularly notice the increased emphasis on standards in the new material on core JavaScript and the DOM.

Another major change in this edition is that the reference section has been split into three distinct parts. First, the core JavaScript material has been separated from the client-side JavaScript material (Part IV) and placed in a section of its own (Part III). This division is for the convenience of JavaScript programmers who are working with the language in an environment other than a web browser and who are not interested in client-side JavaScript.

Second, the new material documenting the W3C DOM has been placed in a section of its own (Part V), separate from the existing client-side JavaScript material. The DOM standard defines an API that is quite distinct from the "legacy" API of traditional client-side JavaScript. Depending on the browser platforms they are targeting, developers typically use one API or the other and usually do not need to switch back and forth. Keeping these two APIs distinct also preserves the organization of the existing client-side reference material, which is convenient for readers of the third edition who upgrade to this edition.

In order to accommodate all the new material without making the book much, much larger, I've gotten rid of reference pages for the trivial properties of objects. These properties are already described once on the reference page for the object, and putting another description in a reference page of its own was redundant and wasteful. Properties that require substantial description, as well as all methods, still have reference pages of their own. Furthermore, the design wizards at O'Reilly have created a new interior design for the book that remains easy and pleasant to read but takes up less space.