Speaking JavaScript

Chapter 19. Regular Expressions

This chapter gives an overview of the JavaScript API for regular expressions. It assumes that you are roughly familiar with how they work. If you are not, there are many good tutorials on the Web. Two examples are:

• Regular-Expressions.info by Jan Goyvaerts
• JavaScript Regular Expression Enlightenment by Cody Lindley

Regular Expression Syntax

The terms used here closely reflect the grammar in the ECMAScript specification. I sometimes deviate to make things easier to understand.

Atoms: General

The syntax for general atoms is as follows:

Special characters

All of the following characters have special meaning:

\ ^ $ . * + ? ( ) [ ] { } |

You can escape them by prefixing a backslash. For example:

> /^(ab)$/.test('(ab)')
false
> /^\(ab\)$/.test('(ab)')
true

Additional special characters are:

• Inside a character class [...]:

  -

• Inside a group that starts with a question mark (?...):

  : = ! < >

  The angle brackets are used only by the XRegExp library (see Chapter 30), to name groups.

Pattern characters

All characters except the aforementioned special ones match themselves.

. (dot)

Matches any JavaScript character (UTF-16 code unit) except line terminators (newline, carriage return, etc.). To really match any character, use [\s\S]. For example:

> /./.test('\n')
false
> /[\s\S]/.test('\n')
true

Character escapes (match single characters)

• Specific control characters include \f (form feed), \n (line feed, newline), \r (carriage return), \t (horizontal tab), and \v ...