Chapter 21
The document Object—Colors, Output, and Properties
The document Object
The document object is a property of the window object. Every window
object, whether it is a full browser window, a frame, or a JavaScript-generated window,
has a document property. The document object encapsulates everything
that exists in the content region of the browser’s window or frame. It is the parent
object of the Web page’s content, including links, anchors, colors, titles, and so
forth. The document object’s properties are spread over the entire HTML
document. Some are commonly placed in the Head portion, while others are normally found in
its Body portion. The document object does not consist of any event handlers. You
might have thought that onLoad, onUnload, and onError belong to
this object, but they are actually properties of the window object.
Not all document object’s properties are HTML-driven content. For example,
the lastModified property provides the date on which the document was last
modified, even though this date is not provided explicitly in the document but rather in
the document’s unseen header.
The document object groups many content-related properties, such as text
color, background color, and others. It also includes more complex properties which are
actually objects, such as forms, links, and image maps.
The title Property
The document’s title is set by default to its complete URL. Most Web page authors
replace this title with their own text. It is specified in the <TITLE></TITLE>
tag pair in the Head portion. The title, which usually appears in the title bar, also
identifies the browser in the operating system’s environment. When the Web page includes
frames, the title bar displays the title of the document which contains the frameset.
Documents providing the content of the frames may include their own titles, but they
don’t affect the title bar.
The document’s title can be scripted via JavaScript as well. Its general reference is
document.title. If the document does not make up the main browser window, the
reference must be preceded by the specific window to which the document belongs.
The title of a frame document is also accessible via JavaScript, using the same procedure.
The document.title property cannot be set by just any JavaScript script, but
only during construction of the entire document. You can use the title property
in many different ways. Suppose you want your document to have a large header containing
the document’s title. Here is such a page’s outline:
<HTML>
<HEAD>
<TITLE>Tomer Shiran's Home Page</TITLE>
</HEAD>
<BODY>
<SCRIPT LANGUAGE="JavaScript">
<!--
document.write("<CENTER><H1>" + document.title + "</H1></CENTER>")
// -->
</SCRIPT>
</BODY>
</HTML>
If you do not include the <TITLE></TITLE> tag pair, the title
defaults to the complete URL of the document, including any search query, if one is
specified. If you place the <TITLE></TITLE> tag pair without text in
between, the title still defaults to the URL. If the text between the opening and closing
tags does not include any characters but one or more space characters, the document is
assumed untitled, and document.title remains an empty string, or a space-filled
string in the case of Microsoft Internet Explorer. The property document.title
never evaluates to the URL, unless you specifically write the URL between the <TITLE></TITLE>
tags.
Because the value of the title bar also identifies the browser application in the
operating system environment, neither Netscape nor Microsoft have made it possible to
explicitly modify it. Since it would not make any sense to identify an application as
scrolling text, for example, the value of the title bar can be assigned only via the document.title
property.
