Chapter 14. The Document Object

Every Window object has a document property. This property refers to a Document object that represents the HTML document displayed in the window. The Document object is probably the most commonly used object in client-side JavaScript. We've already seen several examples in this book that use the write( ) method of the Document object to insert dynamic content into a document while it is being parsed. In addition to the frequently used write( ) method, the Document object defines properties that provide information about the document as a whole: its URL, its last-modified date, the URL of the document that linked to it, the colors in which it is displayed, and so on.

Client-side JavaScript exists to turn static HTML documents into interactive programs -- it is the Document object that gives JavaScript interactive access to the content of otherwise static documents. In addition to the properties that provide information about a document as a whole, the Document object has a number of very important properties that provide information about document content. The forms[] array, for instance, contains Form objects that represent all the HTML forms in the document. And the images[] and applets[] arrays contain objects that represent the images and applets in the document. These arrays and the objects they contain open up a world of possibilities for client-side JavaScript programs, and the bulk of this chapter is devoted to documenting them.

This chapter covers the core features of the Document object that are implemented by virtually every JavaScript-enabled browser. Newer browsers, such as IE 4 and later and Netscape 6 and later, implement a full document object model, or DOM, that gives JavaScript complete access to and control over all document content. These advanced DOM features are covered in Chapter 17.