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.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
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
is a string that contains the flags to add, or if an object is supplied for the pattern, theflags
string will replace any of that object's flags (andlastIndex
will be reset to 0) (as of ES2015). Ifflags
is not specified and a regular expressions object is supplied, that object's flags (andlastIndex
value) will be copied over.flags
may contain any combination of the following characters: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 (see also Binary strings).
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
The Unicode property escapes feature introduces a solution by allowing for a statement as simple as \p{scx=Cyrl}
. One can also use an external resource for getting the complete Unicode block range for different scripts, such as 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
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
RegExp | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
compile | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
dotAll | Chrome Full support 62 | Edge No support No | Firefox No support No | IE No support No | Opera Full support 49 | Safari Full support 12 | WebView Android Full support 62 | Chrome Android Full support 62 | Firefox Android No support No | Opera Android Full support 46 | Safari iOS Full support 12 | Samsung Internet Android Full support 8.0 | nodejs
Full support
8.10.0
|
exec | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
flags | Chrome Full support 49 | Edge No support No | Firefox Full support 37 | IE No support No | Opera Full support 39 | Safari Full support Yes | WebView Android Full support 49 | Chrome Android Full support 49 | Firefox Android Full support 37 | Opera Android Full support 41 | Safari iOS Full support Yes | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
global | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
ignoreCase | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp.input ($_ ) | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
lastIndex | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp.lastMatch ($& ) | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp.lastParen ($+ ) | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp.leftContext ($` ) | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
lookbehind assertions ((?<= ) and (?<! ) ) | Chrome Full support 62 | Edge No support No | Firefox
No support
No
| IE No support No | Opera Full support 49 | Safari No support No | WebView Android Full support 62 | Chrome Android Full support 62 | Firefox Android
No support
No
| Opera Android Full support 46 | Safari iOS No support No | Samsung Internet Android Full support 8.0 | nodejs Full support 8.10.0 |
multiline | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp.$1-$9 | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Named capture groups | Chrome Full support 64 | Edge No support No | Firefox No support No | IE No support No | Opera Full support 51 | Safari Full support 11.1 | WebView Android Full support 64 | Chrome Android Full support 64 | Firefox Android No support No | Opera Android Full support 47 | Safari iOS Full support 11.3 | Samsung Internet Android Full support 9.0 | nodejs
Full support
10.0.0
|
Unicode property escapes (\p{...} ) | Chrome Full support 64 | Edge No support No | Firefox No support No | IE No support No | Opera Full support 51 | Safari Full support 11.1 | WebView Android Full support 64 | Chrome Android Full support 64 | Firefox Android No support No | Opera Android Full support 47 | Safari iOS Full support 11.3 | Samsung Internet Android Full support 9.0 | nodejs
Full support
10.0.0
|
prototype | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp.rightContext ($' ) | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
source | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
sticky | Chrome Full support 49 | Edge Full support 13 | Firefox Full support 3 | IE No support No | Opera Full support 36 | Safari Full support 10 | WebView Android Full support 49 | Chrome Android Full support 49 | Firefox Android Full support 4 | Opera Android Full support 36 | Safari iOS Full support 10 | Samsung Internet Android Full support 5.0 | nodejs Full support Yes |
test | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
toSource | Chrome No support No | Edge No support No | Firefox Full support 1 | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android Full support 4 | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
toString | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
unicode | Chrome Full support 50 | Edge
Full support
12
| Firefox Full support 46 | IE No support No | Opera Full support 37 | Safari Full support 10 | WebView Android Full support Yes | Chrome Android Full support 50 | Firefox Android Full support 46 | Opera Android Full support 37 | Safari iOS Full support 10 | Samsung Internet Android Full support 5.0 | nodejs Full support Yes |
@@match | Chrome Full support 50 | Edge Full support 13 | Firefox Full support 49 | IE No support No | Opera Full support 37 | Safari Full support Yes | WebView Android Full support 50 | Chrome Android Full support 50 | Firefox Android Full support 49 | Opera Android Full support 37 | Safari iOS Full support Yes | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
@@matchAll | Chrome Full support 73 | Edge No support No | Firefox Full support 67 | IE No support No | Opera Full support 60 | Safari No support No | WebView Android Full support 73 | Chrome Android Full support 73 | Firefox Android Full support 67 | Opera Android Full support 52 | Safari iOS No support No | Samsung Internet Android Full support 5.0 | nodejs Full support 12.0.0 |
@@replace | Chrome Full support 50 | Edge No support No | Firefox Full support 49 | IE No support No | Opera Full support 37 | Safari Full support Yes | WebView Android Full support 50 | Chrome Android Full support 50 | Firefox Android Full support 49 | Opera Android Full support 37 | Safari iOS Full support Yes | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
@@search | Chrome Full support 49 | Edge Full support 13 | Firefox Full support 49 | IE No support No | Opera Full support 36 | Safari Full support Yes | WebView Android Full support 49 | Chrome Android Full support 49 | Firefox Android Full support 49 | Opera Android Full support 36 | Safari iOS Full support Yes | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
@@species | Chrome Full support 49 | Edge Full support 13 | Firefox Full support 49 | IE No support No | Opera Full support 36 | Safari Full support Yes | WebView Android Full support 49 | Chrome Android Full support 49 | Firefox Android Full support 49 | Opera Android Full support 36 | Safari iOS Full support Yes | Samsung Internet Android Full support 5.0 | nodejs
Full support
6.5.0
|
@@split | Chrome Full support 50 | Edge No support No | Firefox Full support 49 | IE No support No | Opera Full support 37 | Safari Full support Yes | WebView Android Full support 50 | Chrome Android Full support 50 | Firefox Android Full support 49 | Opera Android Full support 37 | Safari iOS Full support Yes | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
Legend
- Full support
- Full support
- No support
- No support
- 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).