The RegExp
object is used for matching text with a pattern.
For an introduction to regular expressions, read the Regular Expressions chapter in the JavaScript Guide.
Description
Literal notation and constructor
There are two ways to create a RegExp
object: a literal notation and a constructor.
- The literal notation's parameters are enclosed between slashes and do not use quotation marks.
- The constructor function's parameters are not enclosed between slashes but do use quotation marks.
The following three 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 results in 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')
—results in 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 obtain it from another source, such as user input.
Flags in constructor
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:
let re = /\w+/ let re = new RegExp('\\w+')
Perl-like 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.). See also deprecated RegExp
properties.
Constructor
RegExp()
- Creates a new
RegExp
object.
Static properties
get RegExp[@@species]
- The constructor function that is used to create derived objects.
RegExp.lastIndex
- The index at which to start the next match.
Instance properties
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.
Instance 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.toString()
- Returns a string representing the specified object. Overrides the
Object.prototype.toString()
method. 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 substrings.
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.
let re = /(\w+)\s(\w+)/ let str = 'John Smith' let 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.
let text = 'Some text\nAnd some more\r\nAnd yet\rThis is the end' let 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
let 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
.
let str = '#foo#' let 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)
The difference between the sticky flag and the global flag
With the sticky flag y
, the next match has to happen at the lastIndex
position, while with the global flag g
, the match can happen at the lastIndex
position or later:
re = /\d/y; while (r = re.exec("123 456")) console.log(r, "AND re.lastIndex", re.lastIndex); // [ '1', index: 0, input: '123 456', groups: undefined ] AND re.lastIndex 1 // [ '2', index: 1, input: '123 456', groups: undefined ] AND re.lastIndex 2 // [ '3', index: 2, input: '123 456', groups: undefined ] AND re.lastIndex 3 // ... and no more match.
With the global flag g
, all 6 digits would be matched, not just 3.
Regular expression and Unicode characters
\w
and \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.
let text = 'Образец text на русском языке' let regex = /[\u0400-\u04FF]+/g let match = regex.exec(text) console.log(match[0]) // logs 'Образец' console.log(regex.lastIndex) // logs '7' let 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}
.
Extracting sub-domain name from URL
let url = 'http://xxx.domain.com' console.log(/[^.]+/.exec(url)[0].substr(7)) // logs 'xxx'
Instead of using regular expressions for parsing URLs, it is usually better to use the browsers built-in URL parser by using the URL API.
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'RegExp' in that specification. |
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 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp() constructor | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | 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 6 | Safari Full support 3.1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 2 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
dotAll | Chrome Full support 62 | Edge Full support 79 | Firefox Full support 78 | 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 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
flags | Chrome Full support 49 | Edge Full support 79 | Firefox Full support 37 | IE No support No | Opera Full support 39 | Safari Full support 9 | WebView Android Full support 49 | Chrome Android Full support 49 | Firefox Android Full support 37 | Opera Android Full support 41 | Safari iOS Full support 9 | 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 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | 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 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | 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 15 | Safari Full support 3 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 14 | Safari iOS Full support 1 | 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 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp.lastMatch ($& ) | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support 10.5 | Safari Full support 3 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 11 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp.lastParen ($+ ) | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support 10.5 | Safari Full support 3 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 11 | Safari iOS Full support 1 | 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 8 | Safari Full support 3 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
lookbehind assertions ((?<= ) and (?<! ) ) | Chrome Full support 62 | Edge Full support 79 | Firefox Full support 78 | 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 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
RegExp.$1-$9 | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Named capture groups | Chrome Full support 64 | Edge Full support 79 | Firefox Full support 78 | IE No support No | Opera Full support 51 | Safari Full support 11.1 | WebView Android Full support 64 | Chrome Android Full support 64 | Firefox Android No support No | Opera Android Full support 47 | Safari iOS Full support 11.3 | Samsung Internet Android Full support 9.0 | nodejs
Full support
10.0.0
|
Unicode property escapes (\p{...} ) | Chrome Full support 64 | Edge Full support 79 | Firefox Full support 78 | IE No support No | Opera Full support 51 | Safari Full support 11.1 | WebView Android Full support 64 | Chrome Android Full support 64 | Firefox Android No support No | Opera Android Full support 47 | Safari iOS Full support 11.3 | Samsung Internet Android Full support 9.0 | nodejs
Full support
10.0.0
|
RegExp.rightContext ($' ) | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support 8 | Safari Full support 3 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | 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 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | 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 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
toSource | Chrome No support No | Edge No support No | Firefox
No support
1 — 74
| 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 5 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | 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 50 | 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 10 | WebView Android Full support 50 | Chrome Android Full support 50 | Firefox Android Full support 49 | Opera Android Full support 37 | Safari iOS Full support 10 | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
@@matchAll | Chrome Full support 73 | Edge Full support 79 | Firefox Full support 67 | IE No support No | Opera Full support 60 | Safari Full support 13 | WebView Android Full support 73 | Chrome Android Full support 73 | Firefox Android Full support 67 | Opera Android Full support 52 | Safari iOS Full support 13 | Samsung Internet Android Full support 5.0 | nodejs Full support 12.0.0 |
@@replace | Chrome Full support 50 | Edge Full support 79 | Firefox Full support 49 | IE No support No | Opera Full support 37 | Safari Full support 10 | WebView Android Full support 50 | Chrome Android Full support 50 | Firefox Android Full support 49 | Opera Android Full support 37 | Safari iOS Full support 10 | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
@@search | Chrome Full support 50 | Edge Full support 13 | Firefox Full support 49 | IE No support No | Opera Full support 37 | Safari Full support 10 | WebView Android Full support 50 | Chrome Android Full support 50 | Firefox Android Full support 49 | Opera Android Full support 37 | Safari iOS Full support 10 | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
@@species | Chrome Full support 50 | Edge Full support 13 | Firefox Full support 49 | IE No support No | Opera Full support 37 | Safari Full support 10 | WebView Android Full support 50 | Chrome Android Full support 50 | Firefox Android Full support 49 | Opera Android Full support 37 | Safari iOS Full support 10 | Samsung Internet Android Full support 5.0 | nodejs
Full support
6.5.0
|
@@split | Chrome Full support 50 | Edge Full support 79 | Firefox Full support 49 | IE No support No | Opera Full support 37 | Safari Full support 10 | WebView Android Full support 50 | Chrome Android Full support 50 | Firefox Android Full support 49 | Opera Android Full support 37 | Safari iOS Full support 10 | 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).