Reading Information about the Browser
The navigator object isn't part of the browser object hierarchy, but it is another useful object for scripting. This object contains information about the browser version. You can use this object to find out which browser and computer platform the user is running, and your script can change its behavior to match that browser.
NOTE
The navigator object is named after Netscape Navigator, which was the only browser that supported JavaScript when the language first appeared in Navigator 2.0. Despite its Netscape-specific name, this object is now supported in Microsoft Internet Explorer.
Browser-specific scripting can be complicated, and you'll learn more about the navigator object in Hour 14, "Creating Cross-Browser Scripts."