Simple and Useful JavaScript Regular Expression Tutorial

Afshin Mehrabani

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16 Jul 2012CPOL2 min read

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This post discusses some simple and useful JavaScript Regular Expressions

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.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By

Afshin Mehrabani

CEO usabli.ca

Iran (Islamic Republic of)

I am a web developer, the co-founder of usabli.ca.
I love programming and also new technologies on Web Developing such as HTML5 and I always split my time between programming and reading.

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