RegExp

  • Revision slug: JavaScript/Reference/Global_Objects/RegExp
  • Revision title: RegExp
  • Revision id: 16412
  • Created:
  • Creator: Eino
  • Is current revision? No
  • Comment /* Parameters */ sticky tag only in firefox >= 3

Revision Content

This page documents the use of the RegExp object itself and its use as a constructor. For a list of properties and methods inherited by RegExp instances, see RegExp.prototype.

Summary

Creates a regular expression object for matching text according to a pattern.

Syntax

var regex = new RegExp("pattern" [, "flags"]);
var literal = /pattern/flags;

Parameters

pattern
The text of the regular expression.
flags
If specified, flags can have any combination of the following values:
g
global match
i
ignore case
m
match over multiple lines
y
sticky; matches only from the index indicated by the lastIndex property of this regular expression in the target string (and does not attempt to match from any later indexes). This allows the match-only-at-start capabilities of the character "^" to effectively be used at any location in a string by changing the value of the lastIndex property.

{{template.Fx_minversion_note(3, "Support for the <code>y</code> flag was added in Firefox 3.")}}

Description

When using the constructor function, the normal string escape rules (preceding special characters with \ when included in a string) are necessary. For example, the following are equivalent:

var re = new RegExp("\\w+");
var re = /\w+/;

Notice that the parameters to the literal format do not use quotation marks to indicate strings, while the parameters to the constructor function do use quotation marks. So the following expressions create the same regular expression:

/ab+c/i;
new RegExp("ab+c", "i");

Special characters in regular expressions

Character Meaning
\

For characters that are usually treated literally, indicates that the next character is special and not to be interpreted literally.

For example, /b/ matches the character 'b'. By placing a backslash in front of b, that is by using /\b/, the character becomes special to mean match a word boundary.

or

For characters that are usually treated specially, indicates that the next character is not special and should be interpreted literally.

For example, * is a special character that means 0 or more occurrences of the preceding character should be matched; for example, /a*/ means match 0 or more "a"s. To match * literally, precede the it with a backslash; for example, /a\*/ matches 'a*'.

^

Matches beginning of input. If the multiline flag is set to true, also matches immediately after a line break character.

For example, /^A/ does not match the 'A' in "an A", but does match the first 'A' in "An A."

$

Matches end of input. If the multiline flag is set to true, also matches immediately before a line break character.

For example, /t$/ does not match the 't' in "eater", but does match it in "eat".

*

Matches the preceding item 0 or more times.

For example, /bo*/ matches 'boooo' in "A ghost booooed" and 'b' in "A bird warbled", but nothing in "A goat grunted".

+

Matches the preceding item 1 or more times. Equivalent to {1,}.

For example, /a+/ matches the 'a' in "candy" and all the a's in "caaaaaaandy".

?

Matches the preceding item 0 or 1 time.

For example, /e?le?/ matches the 'el' in "angel" and the 'le' in "angle."

If used immediately after any of the quantifiers *, +, ?, or {}, makes the quantifier non-greedy (matching the minimum number of times), as opposed to the default, which is greedy (matching the maximum number of times).

Also used in lookahead assertions, described under (?=), (?!), and (?:) in this table.

.

(The decimal point) matches any single character except the newline characters: \n \r \u2028 or \u2029. ({{mediawiki.external('\\s\\S')}} can be used to match any character including newlines.)

For example, /.n/ matches 'an' and 'on' in "nay, an apple is on the tree", but not 'nay'.

(x)

Matches x and remembers the match. These are called capturing parentheses.

For example, /(foo)/ matches and remembers 'foo' in "foo bar." The matched substring can be recalled from the resulting array's elements {{mediawiki.external(1)}}, ..., {{mediawiki.external('<i>n</i>')}} or from the predefined RegExp object's properties $1, ..., $9.

(?:x)

Matches x but does not remember the match. These are called non-capturing parentheses. The matched substring can not be recalled from the resulting array's elements {{mediawiki.external(1)}}, ..., {{mediawiki.external('<i>n</i>')}} or from the predefined RegExp object's properties $1, ..., $9.

x(?=y)

Matches x only if x is followed by y. For example, /Jack(?=Sprat)/ matches 'Jack' only if it is followed by 'Sprat'. /Jack(?=Sprat|Frost)/ matches 'Jack' only if it is followed by 'Sprat' or 'Frost'. However, neither 'Sprat' nor 'Frost' is part of the match results.

x(?!y)

Matches x only if x is not followed by y. For example, /\d+(?!\.)/ matches a number only if it is not followed by a decimal point.

/\d+(?!\.)/.exec("3.141") matches 141 but not 3.141.

x|y

Matches either x or y.

For example, /green|red/ matches 'green' in "green apple" and 'red' in "red apple."

{n}

Where n is a positive integer. Matches exactly n occurrences of the preceding item.

For example, /a{2}/ doesn't match the 'a' in "candy," but it matches all of the a's in "caandy," and the first two a's in "caaandy."

{n,}

Where n is a positive integer. Matches at least n occurrences of the preceding item.

For example, /a{2,} doesn't match the 'a' in "candy", but matches all of the a's in "caandy" and in "caaaaaaandy."

{n,m}

Where n and m are positive integers. Matches at least n and at most m occurrences of the preceding item.

For example, /a{1,3}/ matches nothing in "cndy", the 'a' in "candy," the first two a's in "caandy," and the first three a's in "caaaaaaandy". Notice that when matching "caaaaaaandy", the match is "aaa", even though the original string had more a's in it.

{{mediawiki.external('<i>xyz</i>')}}

A character set. Matches any one of the enclosed characters. You can specify a range of characters by using a hyphen.

For example, {{mediawiki.external('abcd')}} is the same as {{mediawiki.external('a-d')}}. They match the 'b' in "brisket" and the 'c' in "ache".

{{mediawiki.external('^<i>xyz</i>')}}

A negated or complemented character set. That is, it matches anything that is not enclosed in the brackets. You can specify a range of characters by using a hyphen.

For example, {{mediawiki.external('^abc')}} is the same as {{mediawiki.external('^a-c')}}. They initially match 'r' in "brisket" and 'h' in "chop."

{{mediawiki.external('\\b')}}

Matches a backspace. (Not to be confused with \b.)

\b

Matches a word boundary, such as a space. (Not to be confused with {{mediawiki.external('\\b')}}.)

For example, /\bn\w/ matches the 'no' in "noonday"; /\wy\b/ matches the 'ly' in "possibly yesterday."

\B

Matches a non-word boundary.

For example, /\w\Bn/ matches 'on' in "noonday", and /y\B\w/ matches 'ye' in "possibly yesterday."

\cX

Where X is a letter from A - Z. Matches a control character in a string.

For example, /\cM/ matches control-M in a string.

\d

Matches a digit character in the basic Latin alphabet. Equivalent to {{mediawiki.external('0-9')}}.

Note: In Firefox 2 and earlier, matches a digit character from any alphabet. ({{template.Bug(378738)}})

For example, /\d/ or /{{mediawiki.external('0-9')}}/ matches '2' in "B2 is the suite number."

\D

Matches any non-digit character in the basic Latin alphabet. Equivalent to {{mediawiki.external('^0-9')}}.

Note: In Firefox 2 and earlier, all alphabet. ({{template.Bug(378738)}})

For example, /\D/ or /{{mediawiki.external('^0-9')}}/ matches 'B' in "B2 is the suite number."

\f

Matches a form-feed.

\n

Matches a linefeed.

\r

Matches a carriage return.

\s

Matches a single white space character, including space, tab, form feed, line feed and other unicode spaces.{{template.Ref("equivalent_s")}}

For example, /\s\w*/ matches ' bar' in "foo bar."

\S

Matches a single character other than white space.{{template.Ref("equivalent_S")}}

For example, /\S\w*/ matches 'foo' in "foo bar."

\t

Matches a tab.

\v

Matches a vertical tab.

\w

Matches any alphanumeric character from the basic Latin alphabet, including the underscore. Equivalent to {{mediawiki.external('A-Za-z0-9_')}}.

For example, /\w/ matches 'a' in "apple," '5' in "$5.28," and '3' in "3D."

\W

Matches any character that is not a word character from the basic Latin alphabet. Equivalent to {{mediawiki.external('^A-Za-z0-9_')}}.

For example, /\W/ or /{{mediawiki.external('^$A-Za-z0-9_')}}/ matches '%' in "50%."

\n

Where n is a positive integer. A back reference to the last substring matching the n parenthetical in the regular expression (counting left parentheses).

For example, /apple(,)\sorange\1/ matches 'apple, orange,' in "apple, orange, cherry, peach." A more complete example follows this table.

\0

Matches a NUL character. Do not follow this with another digit.

\xhh

Matches the character with the code hh (two hexadecimal digits)

\uhhhh

Matches the character with the Unicode value hhhh (four hexadecimal digits).

The literal notation provides compilation of the regular expression when the expression is evaluated. Use literal notation when the regular expression will remain constant. For example, if you use literal notation to construct a regular expression used in a loop, the regular expression won't be recompiled on each iteration.

The constructor of the regular expression object, for example, new RegExp("ab+c"), provides runtime compilation of the regular expression. Use the constructor function when you know the regular expression pattern will be changing, or you don't know the pattern and are getting it from another source, such as user input.

  1. {{template.Note("equivalent_s")}}Equivalent to:

{{mediawiki.external('\\t\\n\\v\\f\\r \\u00a0\\u2000\\u2001\\u2002\\u2003\\u2004\\u2005\\u2006\\u2007\\u2008\\u2009\\u200a\\u200b\\u2028\\u2029\\u3000')}}

  1. {{template.Note("equivalent_S")}}Equivalent to:

{{mediawiki.external('^\\t\\n\\v\\f\\r \\u00a0\\u2000\\u2001\\u2002\\u2003\\u2004\\u2005\\u2006\\u2007\\u2008\\u2009\\u200a\\u200b\\u2028\\u2029\\u3000')}}

Properties

prototype
Allows the addition of properties to all objects.

{{template.JSInherits("Function", "Properties", "caller", "constructor", "length", "name")}}

Methods

The global RegExp object has no methods of its own, however, it does inherit some methods through the prototype chain.

{{template.JSInherits("Function", "Methods", "apply", "call", "toSource", "toString", "valueOf")}}

{{template.JSInherits("Object", "Methods", "__defineGetter__", "__defineSetter__", "hasOwnProperty", "isPrototypeOf", "__lookupGetter__", "__lookupSetter__", "propertyIsEnumerable", "unwatch", "watch")}}

Examples

Example: Using a regular expression to change data format

The following script uses the replace method inherited by the String instance to match a name in the format first last and output it in the format last, first. In the replacement text, the script uses $1 and $2 to indicate the results of the corresponding matching parentheses in the regular expression pattern.

var re = /(\w+)\s(\w+)/;
var str = "John Smith";
var newstr = str.replace(re, "$2, $1");
print(newstr);

This displays "Smith, John".

Example: Using a regular expression with the "sticky" flag

This example demonstrates how one could use the sticky flag on regular expressions to match individual lines of multiline input.

var text = "First line\nsecond line";
var regex = /(\S+) line\n?/y;

var match = regex.exec(text);
print(match[1]);  // prints "First"
print(regex.lastIndex); // prints 11

var match2 = regex.exec(text);
print(match2[1]); // prints "Second"
print(regex.lastIndex); // prints "22"

var match3 = regex.exec(text);
print(match3 === null); // prints "true"

See also

{{ wiki.languages( { "fr": "fr/R\u00e9f\u00e9rence_de_JavaScript_1.5_Core/Objets_globaux/RegExp", "ja": "ja/Core_JavaScript_1.5_Reference/Global_Objects/RegExp", "pl": "pl/Dokumentacja_j\u0119zyka_JavaScript_1.5/Obiekty/RegExp" } ) }}

Revision Source

<p>
</p>
<dl><dd> <i><small style="line-height: 100%;">This page documents the use of the <code>RegExp</code> object itself and its use as a constructor. For a list of properties and methods inherited by <code>RegExp</code> instances, see <a href="en/Core_JavaScript_1.5_Reference/Global_Objects/RegExp/prototype">RegExp.prototype</a>.</small></i>
</dd></dl>
<h3 name="Summary"> Summary </h3>
<p>Creates a regular expression object for matching text according to a pattern.
</p>
<h3 name="Syntax"> Syntax </h3>
<pre class="eval">var regex = new RegExp("<i>pattern</i>" <i>[</i>, "<i>flags</i>"<i>]</i>);
var literal = /<i>pattern</i>/<i>flags</i>;
</pre>
<h3 name="Parameters"> Parameters </h3>
<dl><dt> <code>pattern</code>
</dt><dd> The text of the regular expression.
</dd></dl>
<dl><dt> <code>flags</code>
</dt><dd> If specified, flags can have any combination of the following values:
<dl><dt> <code>g</code>
</dt><dd> global match
</dd><dt> <code>i</code>
</dt><dd> ignore case
</dd><dt> <code>m</code>
</dt><dd> match over multiple lines
</dd><dt> <code>y</code>
</dt><dd> sticky; matches only from the index indicated by the <code>lastIndex</code> property of this regular expression in the target string (and does not attempt to match from any later indexes).  This allows the match-only-at-start capabilities of the character "^" to effectively be used at any location in a string by changing the value of the <code>lastIndex</code> property.
</dd></dl>
</dd></dl>
<p>{{template.Fx_minversion_note(3, "Support for the &lt;code&gt;y&lt;/code&gt; flag was added in Firefox 3.")}}
</p>
<h3 name="Description"> Description </h3>
<p>When using the constructor function, the normal string escape rules (preceding special characters with \ when included in a string) are necessary. For example, the following are equivalent:
</p>
<pre class="eval">var re = new RegExp("\\w+");
var re = /\w+/;
</pre>
<p>Notice that the parameters to the literal format do not use quotation marks to indicate strings, while the parameters to the constructor function do use quotation marks. So the following expressions create the same regular expression:
</p>
<pre class="eval">/ab+c/i;
new RegExp("ab+c", "i");
</pre>
<h4 name="Special_characters_in_regular_expressions"> Special characters in regular expressions </h4>
<table class="fullwidth-table">
<tbody><tr>
<td class="header">Character</td>
<td class="header">Meaning</td>
</tr>

<tr>
<td><code>\</code></td>
<td>
<p>For characters that are usually treated literally, indicates that the next character is special and not to be interpreted literally.
</p><p>For example, <code>/b/</code> matches the character 'b'. By placing a backslash in front of b, that is by using <code>/\b/</code>, the character becomes special to mean match a word boundary.
</p><p><i>or</i>
</p><p>For characters that are usually treated specially, indicates that the next character is not special and should be interpreted literally.
</p><p>For example, * is a special character that means 0 or more occurrences of the preceding character should be matched; for example, <code>/a*/</code> means match 0 or more "a"s. To match <code>*</code> literally, precede the it with a backslash; for example, <code>/a\*/</code> matches 'a*'.  
</p>
</td>
</tr>

<tr>
<td><code>^</code></td>
<td>
<p>Matches beginning of input. If the multiline flag is set to true, also matches immediately after a line break character.
</p><p>For example, <code>/^A/</code> does not match the 'A' in "an A", but does match the first 'A' in "An A."  
</p>
</td>
</tr>

<tr>
<td><code>$</code></td>
<td>
<p>Matches end of input. If the multiline flag is set to true, also matches immediately before a line break character.
</p><p>For example, <code>/t$/</code> does not match the 't' in "eater", but does match it in "eat".  
</p>
</td>
</tr>

<tr>
<td><code>*</code></td>
<td>
<p>Matches the preceding item 0 or more times.
</p><p>For example, <code>/bo*/</code> matches 'boooo' in "A ghost booooed" and 'b' in "A bird warbled", but nothing in "A goat grunted".  
</p>
</td>
</tr>

<tr>
<td><code>+</code></td>
<td>
<p>Matches the preceding item 1 or more times. Equivalent to <code>{1,}</code>.
</p><p>For example, <code>/a+/</code> matches the 'a' in "candy" and all the a's in "caaaaaaandy".  
</p>
</td>
</tr>

<tr>
<td><code>?</code></td>
<td>
<p>Matches the preceding item 0 or 1 time.
</p><p>For example, <code>/e?le?/</code> matches the 'el' in "angel" and the 'le' in "angle."
</p><p>If used immediately after any of the quantifiers <code>*</code>, <code>+</code>, <code>?</code>, or <code>{}</code>, makes the quantifier non-greedy (matching the minimum number of times), as opposed to the default, which is greedy (matching the maximum number of times).
</p><p>Also used in lookahead assertions, described under <code>(?=)</code>, <code>(?!)</code>, and <code>(?:)</code> in this table.  
</p>
</td>
</tr>

<tr>
<td><code>.</code></td>
<td>
<p>(The decimal point) matches any single character except the newline characters: \n \r \u2028 or \u2029. (<code>{{mediawiki.external('\\s\\S')}}</code> can be used to match any character including newlines.)
</p><p>For example, <code>/.n/</code> matches 'an' and 'on' in "nay, an apple is on the tree", but not 'nay'.  
</p>
</td>
</tr>

<tr>
<td><code>(<i>x</i>)</code></td>
<td>
<p>Matches <code><i>x</i></code> and remembers the match. These are called capturing parentheses.
</p><p>For example, <code>/(foo)/</code> matches and remembers 'foo' in "foo bar." The matched substring can be recalled from the resulting array's elements <code>{{mediawiki.external(1)}}, ..., {{mediawiki.external('&lt;i&gt;n&lt;/i&gt;')}}</code> or from the predefined <code>RegExp</code> object's properties <code>$1, ..., $9</code>.  
</p>
</td>
</tr>

<tr>
<td><code>(?:<i>x</i>)</code></td>
<td>
<p>Matches <code><i>x</i></code> but does not remember the match. These are called non-capturing parentheses. The matched substring can not be recalled from the resulting array's elements <code>{{mediawiki.external(1)}}, ..., {{mediawiki.external('&lt;i&gt;n&lt;/i&gt;')}}</code> or from the predefined <code>RegExp</code> object's properties <code>$1, ..., $9</code>.  
</p>
</td>
</tr>

<tr>
<td><code><i>x</i>(?=<i>y</i>)</code></td>
<td>
<p>Matches <code><i>x</i></code> only if <code><i>x</i></code> is followed by <code><i>y</i></code>. For example, <code>/Jack(?=Sprat)/</code> matches 'Jack' only if it is followed by 'Sprat'. <code>/Jack(?=Sprat|Frost)/</code> matches 'Jack' only if it is followed by 'Sprat' or 'Frost'. However, neither 'Sprat' nor 'Frost' is part of the match results.  
</p>
</td>
</tr>

<tr>
<td><code><i>x</i>(?!<i>y</i>)</code></td>
<td>
<p>Matches <code><i>x</i></code> only if <code><i>x</i></code> is not followed by <code><i>y</i></code>. For example, <code>/\d+(?!\.)/</code> matches a number only if it is not followed by a decimal point.
</p><p><code>/\d+(?!\.)/.exec("3.141")</code> matches 141 but not 3.141.  
</p>
</td>
</tr>

<tr>
<td><code><i>x</i>|<i>y</i></code></td>
<td>
<p>Matches either <code><i>x</i></code> or <code><i>y</i></code>.
</p><p>For example, <code>/green|red/</code> matches 'green' in "green apple" and 'red' in "red apple."  
</p>
</td>
</tr>

<tr>
<td><code>{<i>n</i>}</code></td>
<td>
<p>Where <code><i>n</i></code> is a positive integer. Matches exactly <code><i>n</i></code> occurrences of the preceding item.
</p><p>For example, <code>/a{2}/</code> doesn't match the 'a' in "candy," but it matches all of the a's in "caandy," and the first two a's in "caaandy."  
</p>
</td>
</tr>

<tr>
<td><code>{<i>n</i>,}</code></td>
<td>
<p>Where <code><i>n</i></code> is a positive integer. Matches at least <code><i>n</i></code> occurrences of the preceding item.
</p><p>For example, <code>/a{2,}</code> doesn't match the 'a' in "candy", but matches all of the a's in "caandy" and in "caaaaaaandy."  
</p>
</td>
</tr>

<tr>
<td><code>{<i>n</i>,<i>m</i>}</code></td>
<td>
<p>Where <code><i>n</i></code> and <code><i>m</i></code> are positive integers. Matches at least <code><i>n</i></code> and at most <code><i>m</i></code> occurrences of the preceding item.
</p><p>For example, <code>/a{1,3}/</code> matches nothing in "cndy", the 'a' in "candy," the first two a's in "caandy," and the first three a's in "caaaaaaandy". Notice that when matching "caaaaaaandy", the match is "aaa", even though the original string had more a's in it.  
</p>
</td>
</tr>

<tr>
<td><code>{{mediawiki.external('&lt;i&gt;xyz&lt;/i&gt;')}}</code></td>
<td>
<p>A character set. Matches any one of the enclosed characters. You can specify a range of characters by using a hyphen.
</p><p>For example, <code>{{mediawiki.external('abcd')}}</code> is the same as <code>{{mediawiki.external('a-d')}}</code>. They match the 'b' in "brisket" and the 'c' in "ache".  
</p>
</td>
</tr>

<tr>
<td><code>{{mediawiki.external('^&lt;i&gt;xyz&lt;/i&gt;')}}</code></td>
<td>
<p>A negated or complemented character set. That is, it matches anything that is not enclosed in the brackets. You can specify a range of characters by using a hyphen.
</p><p>For example, <code>{{mediawiki.external('^abc')}}</code> is the same as <code>{{mediawiki.external('^a-c')}}</code>. They initially match 'r' in "brisket" and 'h' in "chop."  
</p>
</td>
</tr>

<tr>
<td><code>{{mediawiki.external('\\b')}}</code></td>
<td>
<p>Matches a backspace. (Not to be confused with <code>\b</code>.)  
</p>
</td>
</tr>

<tr>
<td><code>\b</code></td>
<td>
<p>Matches a word boundary, such as a space. (Not to be confused with <code>{{mediawiki.external('\\b')}}</code>.)
</p><p>For example, <code>/\bn\w/</code> matches the 'no' in "noonday"; <code>/\wy\b/</code> matches the 'ly' in "possibly yesterday."  
</p>
</td>
</tr>

<tr>
<td><code>\B</code></td>
<td>
<p>Matches a non-word boundary.
</p><p>For example, <code>/\w\Bn/</code> matches 'on' in "noonday", and <code>/y\B\w/</code> matches 'ye' in "possibly yesterday."  
</p>
</td>
</tr>

<tr>
<td><code>\c<i>X</i></code></td>
<td>
<p>Where <code><i>X</i></code> is a letter from A - Z. Matches a control character in a string.
</p><p>For example, <code>/\cM/</code> matches control-M in a string.  
</p>
</td>
</tr>

<tr>
<td><code>\d</code></td>
<td>
<p>Matches a digit character in the basic Latin alphabet. Equivalent to <code>{{mediawiki.external('0-9')}}</code>. 
</p><p><b>Note</b>: In Firefox 2 and earlier, matches a digit character from any alphabet. ({{template.Bug(378738)}})
</p><p>For example, <code>/\d/</code> or <code>/{{mediawiki.external('0-9')}}/</code> matches '2' in "B2 is the suite number."  
</p>
</td>
</tr>

<tr>
<td><code>\D</code></td>
<td>
<p>Matches any non-digit character in the basic Latin alphabet. Equivalent to <code>{{mediawiki.external('^0-9')}}</code>. 
</p><p><b>Note</b>: In Firefox 2 and earlier, all  alphabet. ({{template.Bug(378738)}})
</p><p>For example, <code>/\D/</code> or <code>/{{mediawiki.external('^0-9')}}/</code> matches 'B' in "B2 is the suite number."  
</p>
</td>
</tr>

<tr>
<td><code>\f</code></td>
<td>
<p>Matches a form-feed.  
</p>
</td>
</tr>

<tr>
<td><code>\n</code></td>
<td>
<p>Matches a linefeed.  
</p>
</td>
</tr>

<tr>
<td><code>\r</code></td>
<td>
<p>Matches a carriage return.  
</p>
</td>
</tr>

<tr>
<td><code>\s</code></td>
<td>
<p>Matches a single white space character, including space, tab, form feed, line feed and other unicode spaces.{{template.Ref("equivalent_s")}}
</p><p>For example, <code>/\s\w*/</code> matches ' bar' in "foo bar."  
</p>
</td>
</tr>

<tr>
<td><code>\S</code></td>
<td>
<p>Matches a single character other than white space.{{template.Ref("equivalent_S")}} 
</p><p>For example, <code>/\S\w*/</code> matches 'foo' in "foo bar."  
</p>
</td>
</tr>

<tr>
<td><code>\t</code></td>
<td>
<p>Matches a tab.  
</p>
</td>
</tr>

<tr>
<td><code>\v</code></td>
<td>
<p>Matches a vertical tab.  
</p>
</td>
</tr>

<tr>
<td><code>\w</code></td>
<td>
<p>Matches any alphanumeric character from the basic Latin alphabet, including the underscore. Equivalent to <code>{{mediawiki.external('A-Za-z0-9_')}}</code>.
</p><p>For example, <code>/\w/</code> matches 'a' in "apple," '5' in "$5.28," and '3' in "3D."  
</p>
</td>
</tr>

<tr>
<td><code>\W</code></td>
<td>
<p>Matches any character that is not a word character from the basic Latin alphabet. Equivalent to <code>{{mediawiki.external('^A-Za-z0-9_')}}</code>.
</p><p>For example, <code>/\W/</code> or <code>/{{mediawiki.external('^$A-Za-z0-9_')}}/</code> matches '%' in "50%."  
</p>
</td>
</tr>

<tr>
<td><code>\<i>n</i></code></td>
<td>
<p>Where <code><i>n</i></code> is a positive integer. A back reference to the last substring matching the n parenthetical in the regular expression (counting left parentheses).
</p><p>For example, <code>/apple(,)\sorange\1/</code> matches 'apple, orange,' in "apple, orange, cherry, peach." A more complete example follows this table.  
</p>
</td>
</tr>

<tr>
<td><code>\0</code></td>
<td>
<p>Matches a NUL character. Do not follow this with another digit.  
</p>
</td>
</tr>

<tr>
<td><code>\x<i>hh</i></code></td>
<td>
<p>Matches the character with the code <code><i>hh</i></code> (two hexadecimal digits)  
</p>
</td>
</tr>

<tr>
<td><code>\u<i>hhhh</i></code></td>
<td>
<p>Matches the character with the Unicode value <code><i>hhhh</i></code> (four hexadecimal digits).  
</p>
</td>
</tr>
</tbody></table>
<p>The literal notation provides compilation of the regular expression when the expression is evaluated. Use literal notation when the regular expression will remain constant. For example, if you use literal notation to construct a regular expression used in a loop, the regular expression won't be recompiled on each iteration.
</p><p>The constructor of the regular expression object, for example, <code>new RegExp("ab+c")</code>, provides runtime compilation of the regular expression. Use the constructor function when you know the regular expression pattern will be changing, or you don't know the pattern and are getting it from another source, such as user input.
</p>
<ol><li>{{template.Note("equivalent_s")}}Equivalent to:
</li></ol>
<p><code>{{mediawiki.external('\\t\\n\\v\\f\\r \\u00a0\\u2000\\u2001\\u2002\\u2003\\u2004\\u2005\\u2006\\u2007\\u2008\\u2009\\u200a\\u200b\\u2028\\u2029\\u3000')}}</code>
</p>
<ol><li>{{template.Note("equivalent_S")}}Equivalent to:
</li></ol>
<p><code>{{mediawiki.external('^\\t\\n\\v\\f\\r \\u00a0\\u2000\\u2001\\u2002\\u2003\\u2004\\u2005\\u2006\\u2007\\u2008\\u2009\\u200a\\u200b\\u2028\\u2029\\u3000')}}</code>
</p>
<h3 name="Properties"> Properties </h3>
<dl><dt> <a href="en/Core_JavaScript_1.5_Reference/Global_Objects/RegExp/prototype">prototype</a></dt><dd> Allows the addition of properties to all objects.
</dd></dl>
<p>{{template.JSInherits("Function", "Properties", "caller", "constructor", "length", "name")}}
</p>
<h3 name="Methods"> Methods </h3>
<p>The global <code>RegExp</code> object has no methods of its own, however, it does inherit some methods through the prototype chain.
</p><p>{{template.JSInherits("Function", "Methods", "apply", "call", "toSource", "toString", "valueOf")}}
</p><p>{{template.JSInherits("Object", "Methods", "__defineGetter__", "__defineSetter__", "hasOwnProperty", "isPrototypeOf", "__lookupGetter__", "__lookupSetter__", "propertyIsEnumerable", "unwatch", "watch")}}
</p>
<h3 name="Examples"> Examples </h3>
<h4 name="Example:_Using_a_regular_expression_to_change_data_format"> Example: Using a regular expression to change data format </h4>
<p>The following script uses the <a href="en/Core_JavaScript_1.5_Reference/Global_Objects/String/replace">replace</a> method inherited by the <a href="en/Core_JavaScript_1.5_Reference/Global_Objects/String">String</a> instance to match a name in the format <i>first last</i> and output it in the format <i>last</i>, <i>first</i>. In the replacement text, the script uses <code>$1</code> and <code>$2</code> to indicate the results of the corresponding matching parentheses in the regular expression pattern.
</p>
<pre class="eval">var re = /(\w+)\s(\w+)/;
var str = "John Smith";
var newstr = str.replace(re, "$2, $1");
print(newstr);
</pre>
<p>This displays "Smith, John".
</p>
<h4 name="Example:_Using_a_regular_expression_with_the_.22sticky.22_flag"> Example: Using a regular expression with the "sticky" flag </h4>
<p>This example demonstrates how one could use the sticky flag on regular expressions to match individual lines of multiline input.
</p>
<pre class="eval">var text = "First line\nsecond line";
var regex = /(\S+) line\n?/y;

var match = regex.exec(text);
print(match[1]);  // prints "First"
print(regex.lastIndex); // prints 11

var match2 = regex.exec(text);
print(match2[1]); // prints "Second"
print(regex.lastIndex); // prints "22"

var match3 = regex.exec(text);
print(match3 === null); // prints "true"
</pre>
<h3 name="See_also"> See also </h3>
<ul><li> <a href="en/Core_JavaScript_1.5_Guide/Regular_Expressions">Regular Expressions</a> chapter in the <a href="en/Core_JavaScript_1.5_Guide">JavaScript Guide</a>
</li></ul>
<div class="noinclude">
</div>
{{ wiki.languages( { "fr": "fr/R\u00e9f\u00e9rence_de_JavaScript_1.5_Core/Objets_globaux/RegExp", "ja": "ja/Core_JavaScript_1.5_Reference/Global_Objects/RegExp", "pl": "pl/Dokumentacja_j\u0119zyka_JavaScript_1.5/Obiekty/RegExp" } ) }}
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