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The RegExp constructor creates a regular expression object for matching text with a pattern.

For an introduction to regular expressions, read the Regular Expressions chapter in the JavaScript Guide.

Syntax

Literal, constructor, and factory notations are possible:

/pattern/flags
new RegExp(pattern[, flags])
RegExp(pattern[, flags])

Parameters

pattern
The text of the regular expression or, as of ES5, another RegExp object (or literal) (the latter for the two RegExp constructor notations only). Patterns can include special characters so they can match a wider range of values than would a literal string. 
flags

If specified, flags indicates the flags to add, or if an object is supplied for the pattern, the flags value will replace any of that object's flags (and lastIndex will be reset to 0) (as of ES2015). If flags is not specified and a regular expressions object is supplied, that object's flags (and lastIndex value) will be copied over. The value is a string containing any combination of the following values:

g
global match; find all matches rather than stopping after the first match
i
ignore case; if u flag is also enabled, use Unicode case folding
m
multiline; treat beginning and end characters (^ and $) as working over multiple lines (i.e., match the beginning or end of each line (delimited by \n or \r), not only the very beginning or end of the whole input string)
s
"dotAll"; allows . to match newlines
u
Unicode; treat pattern as a sequence of Unicode code points
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).

Description

There are two ways to create a RegExp object: a literal notation and a constructor. The parameters to the literal notation are enclosed between slashes and do not use quotation marks while the parameters to the constructor function are not enclosed between slashes but do use quotation marks.

The following expressions create the same regular expression:

/ab+c/i;
new RegExp(/ab+c/, 'i'); // literal notation
new RegExp('ab+c', 'i'); // constructor

The literal notation provides a 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.

Starting with ECMAScript 6, new RegExp(/ab+c/, 'i') no longer throws a TypeError ("can't supply flags when constructing one RegExp from another") when the first argument is a RegExp and the second flags argument is present. A new RegExp from the arguments is created instead.

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

Properties

RegExp.prototype
Allows the addition of properties to all objects.
RegExp.length
The value of RegExp.length is 2.
get RegExp[@@species]
The constructor function that is used to create derived objects.
RegExp.lastIndex
The index at which to start the next match.

Methods

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

RegExp prototype objects and instances

Properties

See also deprecated RegExp properties.

Note that several of the RegExp properties have both long and short (Perl-like) names. Both names always refer to the same value. Perl is the programming language from which JavaScript modeled its regular expressions.

RegExp.prototype.constructor
Specifies the function that creates an object's prototype.
RegExp.prototype.flags
A string that contains the flags of the RegExp object.
RegExp.prototype.dotAll
Whether . matches newlines or not.
RegExp.prototype.global
Whether to test the regular expression against all possible matches in a string, or only against the first.
RegExp.prototype.ignoreCase
Whether to ignore case while attempting a match in a string.
RegExp.prototype.multiline
Whether or not to search in strings across multiple lines.
RegExp.prototype.source
The text of the pattern.
RegExp.prototype.sticky
Whether or not the search is sticky.
RegExp.prototype.unicode
Whether or not Unicode features are enabled.

Methods

RegExp.prototype.compile()
(Re-)compiles a regular expression during execution of a script.
RegExp.prototype.exec()
Executes a search for a match in its string parameter.
RegExp.prototype.test()
Tests for a match in its string parameter.
RegExp.prototype[@@match]()
Performs match to given string and returns match result.
RegExp.prototype[@@matchAll]()
Returns all matches of the regular expression against a string.
RegExp.prototype[@@replace]()
Replaces matches in given string with new substring.
RegExp.prototype[@@search]()
Searches the match in given string and returns the index the pattern found in the string.
RegExp.prototype[@@split]()
Splits given string into an array by separating the string into substring.
RegExp.prototype.toSource()
Returns an object literal representing the specified object; you can use this value to create a new object. Overrides the Object.prototype.toSource() method.
RegExp.prototype.toString()
Returns a string representing the specified object. Overrides the Object.prototype.toString() method.

Examples

Using a regular expression to change data format

The following script uses the replace() method of 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');
console.log(newstr);

This displays "Smith, John".

Using regular expression to split lines with different line endings/ends of line/line breaks

The default line ending varies depending on the platform (Unix, Windows, etc.). The line splitting provided in this example works on all platforms.

var text = 'Some text\nAnd some more\r\nAnd yet\rThis is the end';
var lines = text.split(/\r\n|\r|\n/);
console.log(lines); // logs [ 'Some text', 'And some more', 'And yet', 'This is the end' ]

Note that the order of the patterns in the regular expression matters.

Using regular expression on multiple lines

var s = 'Please yes\nmake my day!';
s.match(/yes.*day/);
// Returns null
s.match(/yes[^]*day/);
// Returns ["yes\nmake my day"]

Using a regular expression with the sticky flag

The sticky flag indicates that the regular expression performs sticky matching in the target string by attempting to match starting at RegExp.prototype.lastIndex.

var str = '#foo#';
var regex = /foo/y;

regex.lastIndex = 1;
regex.test(str); // true
regex.lastIndex = 5;
regex.test(str); // false (lastIndex is taken into account with sticky flag)
regex.lastIndex; // 0 (reset after match failure)

Regular expression and Unicode characters

As mentioned above, \w or \W only matches ASCII based characters; for example, "a" to "z", "A" to "Z", "0" to "9" and "_". To match characters from other languages such as Cyrillic or Hebrew, use \uhhhh, where "hhhh" is the character's Unicode value in hexadecimal. This example demonstrates how one can separate out Unicode characters from a word.

var text = 'Образец text на русском языке';
var regex = /[\u0400-\u04FF]+/g;

var match = regex.exec(text);
console.log(match[0]);        // logs 'Образец'
console.log(regex.lastIndex); // logs '7'

var match2 = regex.exec(text);
console.log(match2[0]);       // logs 'на' [did not log 'text']
console.log(regex.lastIndex); // logs '15'

// and so on

Here's an external resource for getting the complete Unicode block range for different scripts: Regexp-Unicode-block.

Extracting sub-domain name from URL

var url = 'http://xxx.domain.com';
console.log(/[^.]+/.exec(url)[0].substr(7)); // logs 'xxx'

Specifications

Specification Status Comment
ECMAScript 3rd Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.1.
ECMAScript 5.1 (ECMA-262)
The definition of 'RegExp' in that specification.
Standard  
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'RegExp' in that specification.
Standard The RegExp constructor no longer throws when the first argument is a RegExp and the second argument is present. Introduces Unicode and sticky flags.
ECMAScript Latest Draft (ECMA-262)
The definition of 'RegExp' in that specification.
Draft  

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
RegExpChrome Full support YesEdge Full support YesFirefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
compile
Deprecated
Chrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
dotAllChrome Full support 62Edge No support NoFirefox No support NoIE No support NoOpera Full support 49Safari Full support 12WebView Android Full support 62Chrome Android Full support 62Edge Mobile No support NoFirefox Android No support NoOpera Android Full support 46Safari iOS Full support 12Samsung Internet Android Full support Yesnodejs Full support 8.10.0
Full support 8.10.0
Full support 8.3.0
Disabled
Disabled From version 8.3.0: this feature is behind the --harmony runtime flag.
execChrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
flagsChrome Full support YesEdge Full support Yes
Disabled
Full support Yes
Disabled
Disabled This feature is behind the Experimental JavaScript Features preference.
Firefox Full support 37IE No support NoOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 37Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support 6.0.0
globalChrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
ignoreCaseChrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
RegExp.input ($_)
Non-standard
Chrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
lastIndexChrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
RegExp.lastMatch ($&)
Non-standard
Chrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
RegExp.lastParen ($+)
Non-standard
Chrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
RegExp.leftContext ($`)
Non-standard
Chrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
lookbehind assertions ((?<= ) and (?<! ))Chrome Full support 62Edge No support NoFirefox No support No
Notes
No support No
Notes
Notes See bug 1225665.
IE No support NoOpera Full support 49Safari No support NoWebView Android Full support 62Chrome Android Full support 62Edge Mobile No support NoFirefox Android No support No
Notes
No support No
Notes
Notes See bug 1225665.
Opera Android Full support 46Safari iOS No support NoSamsung Internet Android Full support Yesnodejs Full support 8.10.0
multilineChrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
RegExp.$1-$9
Non-standard
Chrome Full support YesEdge Full support YesFirefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
Unicode property escapes (\p{...})Chrome Full support 64Edge ? Firefox No support NoIE ? Opera Full support 51Safari ? WebView Android Full support 64Chrome Android Full support 64Edge Mobile ? Firefox Android No support NoOpera Android Full support 47Safari iOS ? Samsung Internet Android Full support Yesnodejs ?
prototypeChrome Full support YesEdge Full support YesFirefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
RegExp.rightContext ($')
Non-standard
Chrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
sourceChrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
stickyChrome Full support 49Edge Full support 13Firefox Full support 3IE No support NoOpera Full support 36Safari Full support 10WebView Android Full support 49Chrome Android Full support 49Edge Mobile Full support YesFirefox Android Full support 4Opera Android Full support 36Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support Yes
testChrome Full support YesEdge Full support 12Firefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
toSource
Non-standard
Chrome No support NoEdge No support NoFirefox Full support 1IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoEdge Mobile No support NoFirefox Android Full support 4Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support Nonodejs No support No
toStringChrome Full support YesEdge Full support YesFirefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes
unicodeChrome Full support 50Edge Full support 12
Notes
Full support 12
Notes
Notes Case folding is implemented in version 13
Firefox Full support 46IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support YesChrome Android Full support 50Edge Mobile Full support YesFirefox Android Full support 46Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support Yes
@@matchChrome Full support YesEdge Full support YesFirefox Full support 49IE No support NoOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 49Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support 6.0.0
@@matchAllChrome Full support 73Edge No support NoFirefox Full support 67IE No support NoOpera Full support 60Safari No support NoWebView Android Full support 73Chrome Android Full support 73Edge Mobile No support NoFirefox Android Full support 67Opera Android Full support YesSafari iOS No support NoSamsung Internet Android Full support Yesnodejs No support No
@@replaceChrome Full support YesEdge Full support YesFirefox Full support 49IE No support NoOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 49Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support 6.0.0
@@searchChrome Full support YesEdge Full support YesFirefox Full support 49IE No support NoOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 49Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support 6.0.0
@@speciesChrome Full support YesEdge Full support YesFirefox Full support 49IE No support NoOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 49Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support 6.5.0
Full support 6.5.0
Full support 6.0.0
Disabled
Disabled From version 6.0.0: this feature is behind the --harmony runtime flag.
@@splitChrome Full support YesEdge Full support YesFirefox Full support 49IE No support NoOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 49Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support 6.0.0

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.
Deprecated. Not for use in new websites.
Deprecated. Not for use in new websites.
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.

Firefox-specific notes

Starting with Firefox 34, in the case of a capturing group with quantifiers preventing its exercise, the matched text for a capturing group is now undefined instead of an empty string:

// Firefox 33 or older
'x'.replace(/x(.)?/g, function(m, group) {
  console.log("'group:" + group + "'");
}); // 'group:'

// Firefox 34 or newer
'x'.replace(/x(.)?/g, function(m, group) {
  console.log("'group:" + group + "'");
}); // 'group:undefined'

Note that due to web compatibility, RegExp.$N will still return an empty string instead of undefined (bug 1053944).

See also