Learning JavaScript, 2nd Edition

Chapter 11. The DOM, or Web Page As Tree

The first release of the World Wide Web Consortium Document Object Model (W3C DOM) was DOM Level 1, issued as a recommendation in 1998. This release helped to define the infrastructure for the DOM—the schema and Application Programming Interface (API) that future versions of the DOM could use as a base of functionality. It also helped to establish a core component of each recommendation that is required for a DOM-compliant user agent (such as a browser); all other specifications are issued as separate, but related, optional modules. This module approach helped to encourage early adoption, and maintain consistency with critical elements.

DOM Level 2 followed in 2000, and expanded on the earlier Level 1 release, while still maintaining consistency with the earlier release. You were already exposed to one aspect of this release in our discussion of Level 2 event handling in Chapter 7. DOM Level 2 added increased support for Cascading Style Sheets (CSS), improved access for document elements, and namespace support in the XML recommendation.

DOM Level 3 was released in 2004. In addition to extensions and improvements to the previous releases, this version adds modules to extend support for web services, as well as increased support for XML, including XPath support. DOM Level 3 is the last of the W3C levels—at least, the last planned W3C level release.

This chapter doesn’t provide a complete reference for all of the objects in the DOM APIs. ...