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.^[1]

^[1] The term "regular expression" is an obscure one that dates back many years. The syntax used to describe a textual pattern is indeed a type of expression. However, as we'll see, that syntax is far from regular! A regular expression is sometimes called a "regexp" or even an "RE."

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.