In this prescription we take a break from Dynamic HTML, and turn to another fourth-generation browser feature: Pattern Matching and Regular Expressions. Regular Expressions have always been a powerful tool in the arsenal of every Unix system administrator, and subsequentially every Perl programmer. Recently, these capabilities were introduced to JavaScript, in Netscape Navigator 4.0x and Microsoft Internet Explorer 4.0. In this in-depth column we'll show you several practical examples, ranging from a feedback form, through advanced string evaluation. In each example you'll learn how you can use regular expressions in JavaScript to analyze the user's input and verify such things as a false or malformed e-mail address or phone number.

This column consists of two parts. The first part covers regular expressions and pattern matching in general, while the second deals with the JavaScript implementation. If you're familiar with Perl or Unix shell prorgamming, you probably won't need to read the first part. However, we suggest you scan it to refresh your memory. The second part of this column consists of useful examples for you to cut and paste, including a general feedback form (no CGI here). In this column you'll find out:

Pattern Matching and Regular Exressions

1. What you can do with regular expressions.
2. How to use various modifiers with matching operators.
3. How to construct regular expressions.
4. What rules apply to all regular expressions.
5. How to use values (backreferences) inside and after a regexp.
6. How to perform substitution commands.

JavaScript Regular Expressions

1. How to define regular expressions.
2. How to use the regular expression methods.
3. How to use backreferences.
4. How to create a general feedback form.
5. How to provide a workaround for older browsers.

Perl is the programming language from which JavaScript modeled its regular expressions. Thus, the first part of this column deals with regular expressions in Perl (with some JavaScript notes). It's based on the book "Programming Perl, 2nd Edition" by Larry Wall, Tom Christiansen, and Randal L. Schwartz (ISBN 1-56592-149-6).