Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

13.7 The Screen Object

In
JavaScript 1.2, the screen property of a Window
object refers to a Screen object that provides information about the
size of the user's display and the number of colors available
on it. The width and
height properties specify the
size of the display in pixels. The
availWidth and availHeight
properties specify the display size that is actually available; they
exclude the space required by features such as the Windows taskbar.
You can use these properties to help you decide what size images to
include in a document, for example, or what size windows to create in
a program that creates multiple browser windows.

The colorDepth property
specifies the base-2 logarithm
of the number of colors that can be
displayed. Often, this value is the same as the number of bits per
pixel used by the display. For example, an 8-bit display can display
256 colors, and if all of these colors were available for use by the
browser, the screen.colorDepth property would be
8. In some circumstances, however, the browser may restrict itself to
a subset of the available colors, and you might find a
screen.colorDepth value that is lower than the
bits-per-pixel value of the screen. If you have several versions of
an image that were defined using different numbers of colors, you can
test this colorDepth property to decide which
version to include in a document.

Example 13-4, later in this chapter, shows how the
Screen object can be used.