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.
There are two ways to create a RegExp
object: a literal notation and a constructor.
The following three expressions create the same regular expression object:
let re = /ab+c/i; // literal notation let re = new RegExp('ab+c', 'i') // constructor with string pattern as first argument let re = new RegExp(/ab+c/, 'i') // constructor with regular expression literal as first argument (Starting with ECMAScript 6)
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.
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+')
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.
RegExp()
RegExp
object.get RegExp[@@species]
RegExp.lastIndex
RegExp.prototype.flags
RegExp
object.RegExp.prototype.dotAll
.
matches newlines or not.RegExp.prototype.global
RegExp.prototype.ignoreCase
RegExp.prototype.multiline
RegExp.prototype.source
RegExp.prototype.sticky
RegExp.prototype.unicode
RegExp.prototype.compile()
RegExp.prototype.exec()
RegExp.prototype.test()
RegExp.prototype.toString()
Object.prototype.toString()
method.RegExp.prototype[@@match]()
RegExp.prototype[@@matchAll]()
RegExp.prototype[@@replace]()
RegExp.prototype[@@search]()
RegExp.prototype[@@split]()
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"
.
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.
let s = 'Please yes\nmake my day!' s.match(/yes.*day/); // Returns null s.match(/yes[^]*day/); // Returns ["yes\nmake my day"]
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)
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.
\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}
.
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.
Desktop | ||||||
---|---|---|---|---|---|---|
RegExp |
1 | 12 | 1 | 4 | 5 | 1 |
RegExp() constructor |
1 | 12 | 1 | 4 | 5 | 1 |
compile
|
1 | 12 | 1 | 4 | 6 | 3.1 |
dotAll |
62 | 79 | 78 | No | 49 | 12 |
exec |
1 | 12 | 1 | 4 | 5 | 1 |
flags |
49 | 79 | 37 | No | 39 | 9 |
global |
1 | 12 | 1 | 5.5 | 5 | 1 |
ignoreCase |
1 | 12 | 1 | 5.5 | 5 | 1 |
RegExp.input ($_ )
|
1 | 12 | 1 | 5.5 | 15 | 3 |
lastIndex |
1 | 12 | 1 | 5.5 | 5 | 1 |
RegExp.lastMatch ($& )
|
1 | 12 | 1 | 5.5 | 10.5 | 3 |
RegExp.lastParen ($+ )
|
1 | 12 | 1 | 5.5 | 10.5 | 3 |
RegExp.leftContext ($` )
|
1 | 12 | 1 | 5.5 | 8 | 3 |
lookbehind assertions ((?<= ) and (?<! ) ) |
62 | 79 | 78 | No | 49 | No |
multiline |
1 | 12 | 1 | 5.5 | 5 | 1 |
RegExp.$1-$9 |
1 | 12 | 1 | 4 | 5 | 1 |
Named capture groups | 64 | 79 | 78 | No | 51 | 11.1 |
Unicode property escapes (\p{...} ) |
64 | 79 | 78 | No | 51 | 11.1 |
RegExp.rightContext ($' )
|
1 | 12 | 1 | 5.5 | 8 | 3 |
source |
1 | 12 | 1 | 4 | 5 | 1 |
sticky |
49 | 13 | 3 | No | 36 | 10 |
test |
1 | 12 | 1 | 4 | 5 | 1 |
toSource
|
No | No | 1 — 74
|
No | No | No |
toString |
1 | 12 | 1 | 4 | 5 | 1 |
unicode |
50 | 12
|
46 | No | 37 | 10 |
@@match |
50 | 13 | 49 | No | 37 | 10 |
@@matchAll |
73 | 79 | 67 | No | 60 | 13 |
@@replace |
50 | 79 | 49 | No | 37 | 10 |
@@search |
50 | 13 | 49 | No | 37 | 10 |
@@species |
50 | 13 | 49 | No | 37 | 10 |
@@split |
50 | 79 | 49 | No | 37 | 10 |
Mobile | ||||||
---|---|---|---|---|---|---|
RegExp |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
RegExp() constructor |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
compile
|
1 | 18 | 4 | 10.1 | 2 | 1.0 |
dotAll |
62 | 62 | No | 46 | 12 | 8.0 |
exec |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
flags |
49 | 49 | 37 | 41 | 9 | 5.0 |
global |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
ignoreCase |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
RegExp.input ($_ )
|
1 | 18 | 4 | 14 | 1 | 1.0 |
lastIndex |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
RegExp.lastMatch ($& )
|
1 | 18 | 4 | 11 | 1 | 1.0 |
RegExp.lastParen ($+ )
|
1 | 18 | 4 | 11 | 1 | 1.0 |
RegExp.leftContext ($` )
|
1 | 18 | 4 | 10.1 | 1 | 1.0 |
lookbehind assertions ((?<= ) and (?<! ) ) |
62 | 62 | No
|
46 | No | 8.0 |
multiline |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
RegExp.$1-$9 |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
Named capture groups | 64 | 64 | No | 47 | 11.3 | 9.0 |
Unicode property escapes (\p{...} ) |
64 | 64 | No | 47 | 11.3 | 9.0 |
RegExp.rightContext ($' )
|
1 | 18 | 4 | 10.1 | 1 | 1.0 |
source |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
sticky |
49 | 49 | 4 | 36 | 10 | 5.0 |
test |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
toSource
|
No | No | 4 | No | No | No |
toString |
1 | 18 | 4 | 10.1 | 1 | 1.0 |
unicode |
50 | 50 | 46 | 37 | 10 | 5.0 |
@@match |
50 | 50 | 49 | 37 | 10 | 5.0 |
@@matchAll |
73 | 73 | 67 | 52 | 13 | 5.0 |
@@replace |
50 | 50 | 49 | 37 | 10 | 5.0 |
@@search |
50 | 50 | 49 | 37 | 10 | 5.0 |
@@species |
50 | 50 | 49 | 37 | 10 | 5.0 |
@@split |
50 | 50 | 49 | 37 | 10 | 5.0 |
Server | |
---|---|
RegExp |
Yes |
RegExp() constructor |
Yes |
compile
|
Yes |
dotAll |
8.10.0
|
exec |
Yes |
flags |
6.0.0 |
global |
Yes |
ignoreCase |
Yes |
RegExp.input ($_ )
|
Yes |
lastIndex |
Yes |
RegExp.lastMatch ($& )
|
Yes |
RegExp.lastParen ($+ )
|
Yes |
RegExp.leftContext ($` )
|
Yes |
lookbehind assertions ((?<= ) and (?<! ) ) |
8.10.0 |
multiline |
Yes |
RegExp.$1-$9 |
Yes |
Named capture groups | 10.0.0
|
Unicode property escapes (\p{...} ) |
10.0.0
|
RegExp.rightContext ($' )
|
Yes |
source |
Yes |
sticky |
Yes |
test |
Yes |
toSource
|
No |
toString |
Yes |
unicode |
Yes |
@@match |
6.0.0 |
@@matchAll |
12.0.0 |
@@replace |
6.0.0 |
@@search |
6.0.0 |
@@species |
6.5.0
|
@@split |
6.0.0 |
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).
String.prototype.match()
String.prototype.replace()
String.prototype.split()
© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp