This is a tutorial that detects a user's information client-side. It is taught with the learn by example teaching method in mind. It covers browser type, version, codename, the OS, screen size, color, whether java is enabled or not, for netscape it detects IP and Host, and it teaches you a way to detect the Javascript version!
There are several different browsers and versions out there, thus you, the programmer, do not know what JavaScript capabilities the user has. Insuring that the scripts you write run in most users browser can be done in a few different ways. One way is to ask the user what browser they are using, via JavaScript, and to then program accourdingly. This tutorial shows you how.