JavaScript® Bible, Seventh Edition

Chapter 25. Document Object Model Essentials

IN THIS CHAPTER

• Object models versus browser versions

• Proprietary model extensions

• Structure of the W3C DOM

• Scripting trends

Without question, the biggest challenge facing client-side web scripters is the sometimes-baffling array of document object models (DOMs) that have competed for our attention throughout the short history of scriptable browsers. Netscape got the ball rolling in Navigator 2 with the first object model. By the time version 4 browsers came around, the original object model had gained not only some useful cross-browser features, but also a host of features that were unique to Navigator or Internet Explorer. The object models were diverging, causing no end of headaches for page authors whose scripts had to run on as many browsers as possible. A ray of hope emerged from the standards process of the World Wide Web Consortium (W3C) in the form of a DOM recommendation. The DOM brought forward much of the original object model, plus new ways of consistently addressing every object in a document. The goal of this chapter is to put each of the object models into perspective and help you understand how modern browsers have alleviated most of the object model compatibility problems. But before we get to those specifics, let's examine the role of the object model in designing scripted applications.

The Object Model Hierarchy

The tutorial chapters of Part II introduced the fundamental ideas behind a document object hierarchy in scriptable ...