Unlike CGI scripts, JavaScript is interpreted by the client. There are currently many clients that support JavaScript, including Netscape Navigator 2.0x, Netscape Navigator 3.0x, Netscape Navigator 4.0x, Microsoft Internet Explorer 3.0x, and Microsoft Internet Explorer 4.0. So when you write a script and embed it in your site, you know it will be interpreted by different interpreters with unequal capabilities and features. Unlike server-side scripts which you have full control over their interpretation, client-side scripts are executed by the user's browser.

Each browser supports different JavaScript features, and also "features" its own bugs. Some bugs are platform-specific, while others are browser-specific. Some objects are supported by Navigator 3.0x, 4.0x, and Internet Explorer 4.0, but are not supported by Navigator 2.0x and Internet Explorer 3.0x. In this column we'll nail down these compatibility issues using several reliable techniques. You'll learn:

1. How to determine which browser the user is running.
2. How to find out if a specific object exists.
3. How to find out if a specific method exists.
4. How to ignore errors when they occur.
5. How to cut & paste common object detection routines.