Simple and Useful JavaScript Regular Expression Tutorial

• Download sample source code - 972 B

Introduction

Regular Expression is a very important part of any language programming because of its ability to help programmers to write fast and pure applications.

You Don't Know What a Regular Expression Is?

A regular expression is an object that describes a pattern of characters.

Regular expressions are used to perform pattern-matching and "search-and-replace" functions on text. 

Web developer can also use Regular Expression in JavaScript. Now I describe some simple examples of using Regular Expression in JavaScript.

The overall syntax should look like:

/pattern/modifiers

• pattern specifies the search pattern
• modifiers specify if our search should be case-sensitive, global, etc.

Modifiers Table

Modifier	Description
i	Perform case-insensitive matching
g	Perform a global match (find all matches rather than stopping after the first match)
m	Perform multiline matching

To compile and use Regular Expression, you can use three useful functions.

Regular Expression Object Methods

Method	Description
compile()	Compiles a regular expression
exec()	Tests for a match in a string. Returns the first match
test()	Tests for a match in a string. Returns true or false

Character Escapes  (Metacharacters)

Metacharacter	Description
.	Find a single character, except newline or line terminator
\w	Find a word character
\W	Find a non-word character
\d	Find a digit
\D	Find a non-digit character
\s	Find a whitespace character
\S	Find a non-whitespace character
\b	Find a match at the beginning/end of a word
\B	Find a match not at the beginning/end of a word
\0	Find a NUL character
\n	Find a new line character
\f	Find a form feed character
\r	Find a carriage return character
\t	Find a tab character
\v	Find a vertical tab character
\xxx	Find the character specified by an octal number xxx
\xdd	Find the character specified by a hexadecimal number dd
\uxxxx	Find the Unicode character specified by a hexadecimal number xxxx

Metacharacter table from W3Schools.  

Example 

Test sentence: Sometext sometext sometext

Expression	Test Result
/sometext/	Sometext sometext sometext
/sometext/i	Sometext sometext sometext
/sometext/g	Sometext sometext sometext
/sometext/gi	Sometext sometext sometext
/some/	Sometext sometext sometext
/some/i	Sometext sometext sometext
/some/g	Sometext sometext sometext
/some/ig	Sometext sometext sometext

It's easy!

In the next article, I will show you Regular Expression performance in some cases and also how to make simple and pure Regular Expressions.

History

• 19 May, 2011: Initial version.
• 1 June, 2011: Added sample source code.
• 16 July, 2012: Add metacharacters table.