JavaScript: The Definitive Guide, Fourth Edition

DOM Compatibility with Netscape 4

Netscape 4 does not even come close to implementing the DOM standard. In particular, Netscape 4 provides no way to access or set attributes on arbitrary elements of a document. Netscape 4 supports the Level 0 DOM API, of course, so elements such as forms and links can be accessed through the forms[] and links[] arrays, but there is no general way to traverse the children of these elements or set arbitrary attributes on them. Furthermore, Netscape 4 does not have the ability to “reflow” document content in response to changes in element size.

Despite these restrictions, Netscape 4 does provide an API that allows access to and manipulation of the crucial “dynamic elements” used to implement DHTML effects. In the Netscape 4 API, these elements are known as layers ; they float above the rest of the document and can be moved, resized, and modified independently of the other elements of the document. Layers are typically implemented using CSS style sheets, and the Netscape 4 Layer API is discussed in detail in Chapter 18.

What follows is simply an overview that explains how you can create, access, and modify the content of individual layer elements within a document. Although Netscape 4 does not support anything like the DOM standard, its Layer API allows you to achieve some of the same dynamic effects that are possible with the standard API. Note that the Layer API was submitted to the W3C for consideration as part of the DOM standard, but no part ...