BOM and DOM – an overview

The JavaScript code in a page has access to a number of objects. These objects can be divided into the following types:

• Core ECMAScript objects : All the objects mentioned in the previous chapters

• DOM: Objects that have to do with the currently loaded page (the page is also called the document)

• BOM: Objects that deal with everything outside the page (the browser window and the desktop screen)

DOM stands for Document Object Model and BOM for Browser Object Model.

The DOM is a standard, governed by the World Wide Web Consortium (W3C) and has different versions, called levels, such as DOM Level 1, DOM Level 2, and so on. Browsers in use today have different degrees of compliance with the standard but in general, they almost all completely implement DOM Level 1. The DOM was standardized post-factum, after the browser vendors had each implemented their own ways to access the document. The legacy part (from before the W3C took over) is still around and is referred to as...