In this column we continue our review of Internet Explorer 5.0. We focus here on one of IE 5.0's major additions to JavaScript: exception handling. Exception handling is a key feature of modern programming languages such as C++, Java, and VBScript. By adding exception handling to its syntax, Microsoft promoted JavaScript to C++'s and Java's standard of languages. Exception handling is based on a syntax that allows the programmer to differentiate between normal-processing code and error-processing code. In industrial-strength code, almost half of the lines deal with errors and exceptions. Separating exception handling code from the other lines makes the code much easier to read, maintain, and modify. Up till now, some programmers preferred VBScript over JavaScript because JavaScript did not support exception handling. Since JavaScript is superior to VBScript in many other ways, we foresee a movement of VBScript programmers to the JavaScript camp.

In this column we'll teach you the basics of exception handling and how to use JavaScript's syntax to take advantage of it. We show you several examples that demonstrate the idea and its implementation. We also emphasize the difference between exception handling in JavaScript and in other languages. In particular we'll show you:

• How to write an exception-handling code for JavaScript-thrown exceptions.
• How to write an exception-handling code for user-thrown exceptions.
• How to write an exception-handling code for handling user-thrown exceptions in a real application.
• How to distinguish between JavaScript's exception handling and C++'s and Java's.
• How to distinguish between JavaScript's exception handling and VBScript's.
• How to workaround inconsistencies between JavaScript and VBScript.