JavaScript: The Definitive Guide, Fourth Edition

Chapter 10.  Pattern Matching with Regular Expressions

A regular expression is an object that describes a pattern of characters. The JavaScript RegExp class represents regular expressions, and both String and RegExp define methods that use regular expressions to perform powerful pattern-matching and search-and-replace functions on text.^[36]

JavaScript regular expressions were standardized in ECMAScript v3. JavaScript 1.2 implements a subset of the regular expression features required by ECMAScript v3, and JavaScript 1.5 implements the full standard. JavaScript regular expressions are strongly based on the regular expression facilities of the Perl programming language. Roughly speaking, we can say that JavaScript 1.2 implements Perl 4 regular expressions, and JavaScript 1.5 implements a large subset of Perl 5 regular expressions.

This chapter begins by defining the syntax that regular expressions use to describe textual patterns. Then it moves on to describe the String and RegExp methods that use regular expressions.

Defining Regular Expressions

In JavaScript, regular expressions are represented by RegExp objects. RegExp objects may be created with the RegExp( ) constructor, of course, but they are more often created using a special literal syntax. Just as string literals are specified as characters within quotation marks, regular expression literals are specified as characters within a pair of slash (/) characters. Thus, your JavaScript code may contain lines like this:

var pattern ...