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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.
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) to copy (the latter for the two RegExp constructor notations only).
flags
-
If specified,
flags
indicates the flags to add, or if an object is supplied for the pattern, theflags
value 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. 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. To indicate strings, the parameters to the literal notation do not use quotation marks 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'); new RegExp(/ab+c/, 'i');
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+');
Special characters meaning in regular expressions
- Character Classes
- Character Sets
- Boundaries
- Alternation
- Grouping and back references
- Quantifiers
- Assertions
Character Classes | |
---|---|
Character | Meaning |
. |
(The dot, the decimal point) matches any single character except line terminators: Inside a character set, the dot loses its special meaning and matches a literal dot. Note that the ES2018 added the For example, |
\d |
Matches any digit (Arabic numeral). Equivalent to For example, |
\D |
Matches any character that is not a digit (Arabic numeral). Equivalent to For example, |
\w |
Matches any alphanumeric character from the basic Latin alphabet, including the underscore. Equivalent to For example, |
\W |
Matches any character that is not a word character from the basic Latin alphabet. Equivalent to For example, |
\s |
Matches a single white space character, including space, tab, form feed, line feed and other Unicode spaces. Equivalent to For example, |
\S |
Matches a single character other than white space. Equivalent to For example, |
\t |
Matches a horizontal tab. |
\r |
Matches a carriage return. |
\n |
Matches a linefeed. |
\v |
Matches a vertical tab. |
\f |
Matches a form-feed. |
[\b] |
Matches a backspace. (Not to be confused with \b ) |
\0 |
Matches a NUL character. Do not follow this with another digit. |
\cX |
Where For example, |
\xhh |
Matches the character with the code hh (two hexadecimal digits). |
\uhhhh |
Matches a UTF-16 code-unit with the value hhhh (four hexadecimal digits). |
\u{hhhh} or \u{hhhhh} |
(only when u flag is set) Matches the character with the Unicode value U+hhhh or U+hhhhh (hexadecimal digits). |
\ |
For characters that are usually treated literally, indicates that the next character is special and not to be interpreted literally. For example, 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, |
Character Sets | |
Character | Meaning |
[xyz] |
A character set. Matches any one of the enclosed characters. You can specify a range of characters by using a hyphen, but if the hyphen appears as the first or last character enclosed in the square brackets it is taken as a literal hyphen to be included in the character set as a normal character. It is also possible to include a character class in a character set. For example, For example, [abcd-] and [-abcd] match the "b" in "brisket", the "c" in "chop" and the "-" (hyphen) in "non-profit". For example, [\w-] is the same as [A-Za-z0-9_-]. They match the "b" in "brisket", the "c" in "chop" and the "n" in "non-profit". |
|
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, but if the hyphen appears as the first or last character enclosed in the square brackets it is taken as a literal hyphen to be included in the character set as a normal character. For example, |
Alternation | |
Character | Meaning |
x|y |
Matches either For example, |
Boundaries | |
Character | Meaning |
^ |
Matches beginning of input. If the multiline flag is set to true, also matches immediately after a line break character. For example, |
$ |
Matches end of input. If the multiline flag is set to true, also matches immediately before a line break character. For example, |
\b |
Matches a word boundary. This is the position where a word character is not followed or preceded by another word-character, such as between a letter and a space. Note that a matched word boundary is not included in the match. In other words, the length of a matched word boundary is zero. Examples: |
\B |
Matches a non-word boundary. This is a position where the previous and next character are of the same type: Either both must be words, or both must be non-words. Such as between two letters or between two spaces. The beginning and end of a string are considered non-words. Same as the matched word boundary, the matched non-word boundary is also not included in the match. For example, |
Grouping and back references | |
Character | Meaning |
(x) |
Matches For example, The capturing groups are numbered according to the order of left parentheses of capturing groups, starting from 1. The matched substring can be recalled from the resulting array's elements Capturing groups have a performance penalty. If you don't need the matched substring to be recalled, prefer non-capturing parentheses (see below). |
\n |
Where For example, |
(?:x) |
Matches x but does not remember the match. These are called non-capturing groups. The matched substring cannot be recalled from the resulting array's elements [1], ..., [n] or from the predefined RegExp object's properties $1, ..., $9 . |
Quantifiers | |
Character | Meaning |
x* |
Matches the preceding item x 0 or more times. For example, |
x+ |
Matches the preceding item x 1 or more times. Equivalent to For example, |
x? |
Matches the preceding item x 0 or 1 time. For example, If used immediately after any of the quantifiers |
x{n} |
Where For example, |
x{n,} |
Where For example, |
x{n,m} |
Where For example, |
|
Matches the preceding item x like For example, Quantifiers without |
Assertions | |
Character | Meaning |
x(?=y) |
Matches For example, / |
x(?!y) |
Matches For example, |
(?<=y)x |
Matches For example, / |
(?<!y)x |
Matches For example, |
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
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Basic support | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
compile | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
exec | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
flags | Chrome Full support Yes | Edge
Full support
Yes
| Firefox Full support 37 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 37 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support 6.0.0 |
global | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
ignoreCase | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
RegExp.input ($_ ) | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
lastIndex | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
RegExp.lastMatch ($& ) | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
RegExp.lastParen ($+ ) | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
RegExp.leftContext ($` ) | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | 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 | Edge Mobile No support No | Firefox Android
No support
No
| Opera Android Full support 49 | Safari iOS No support No | Samsung Internet Android ? | nodejs Full support 8.10.0 |
multiline | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
RegExp.$1-$9 | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
Unicode property escapes (\p{...} ) | Chrome Full support 64 | Edge ? | Firefox No support No | IE ? | Opera Full support 51 | Safari ? | WebView Android Full support 64 | Chrome Android Full support 64 | Edge Mobile ? | Firefox Android No support No | Opera Android Full support 51 | Safari iOS ? | Samsung Internet Android ? | nodejs ? |
prototype | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
RegExp.rightContext ($' ) | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
source | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | 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 | Edge Mobile Full support Yes | 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 Yes | Edge Full support 12 | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | 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 | Edge Mobile 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 Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | 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 | Edge Mobile Full support Yes | 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 Yes | Edge Full support Yes | Firefox Full support 49 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 49 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support 6.0.0 |
@@matchAll | Chrome Full support 73 | Edge No support No | Firefox No support No | IE No support No | Opera Full support 60 | Safari No support No | WebView Android Full support 73 | Chrome Android Full support 73 | Edge Mobile No support No | Firefox Android No support No | Opera Android Full support Yes | Safari iOS No support No | Samsung Internet Android Full support Yes | nodejs No support No |
@@replace | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 49 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 49 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support 6.0.0 |
@@search | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 49 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 49 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support 6.0.0 |
@@species | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 49 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 49 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs
Full support
6.5.0
|
@@split | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 49 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 49 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs 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).