JavaScript: The Definitive Guide, 6th Edition

Browser and Screen Information

Scripts sometimes need to obtain information about the web browser in which they are running or the desktop on which the browser appears. This section describes the navigator and screen properties of the Window object. Those properties refer to Navigator and Screen objects, respectively, and these objects provide information that allows a script to customize its behavior based on its environment.

The Navigator Object

The navigator property of a Window object refers to a Navigator object that contains browser vendor and version number information. The Navigator object is named after the early Navigator browser from Netscape, but it is also supported by all other browsers. (IE also supports clientInformation as a vendor-neutral synonym for navigator. Unfortunately, other browsers have not adopted this more sensibly named property.)

In the past, the Navigator object was commonly used by scripts to determine if they were running in Internet Explorer or Netscape. This “browser-sniffing” approach is problematic because it requires constant tweaking as new browsers and new versions of existing browsers are introduced. Today, feature testing (see Feature Testing) is preferred: rather than making assumptions about particular browser versions and their features, you simply test for the feature (i.e., the method or property) you need.

Browser sniffing is sometimes still valuable, however, such as when you need to work around a specific bug that exists in a specific ...