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Regular expressions are patterns used to match character combinations in strings. In JavaScript, regular expressions are also objects. These patterns are used with the exec() and test() methods of RegExp, and with the match()matchAll(), replace()replaceAll(), search(), and split() methods of String. This chapter describes JavaScript regular expressions.

Creating a regular expression

You construct a regular expression in one of two ways:

  • Using a regular expression literal, which consists of a pattern enclosed between slashes, as follows:

    let re = /ab+c/;
    

    Regular expression literals provide compilation of the regular expression when the script is loaded. If the regular expression remains constant, using this can improve performance.

  • Or calling the constructor function of the RegExp object, as follows:

    let re = new RegExp('ab+c');
    

    Using the constructor function 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.

Writing a regular expression pattern

A regular expression pattern is composed of simple characters, such as /abc/, or a combination of simple and special characters, such as /ab*c/ or /Chapter (\d+)\.\d*/. The last example includes parentheses, which are used as a memory device. The match made with this part of the pattern is remembered for later use, as described in Using groups.

Note: If you are already familiar with the forms of a regular expression, you may also read the cheatsheet for a quick lookup for a specific pattern/construct.

Using simple patterns

Simple patterns are constructed of characters for which you want to find a direct match. For example, the pattern /abc/ matches character combinations in strings only when the exact sequence "abc" occurs (all characters together and in that order). Such a match would succeed in the strings "Hi, do you know your abc's?" and "The latest airplane designs evolved from slabcraft." In both cases the match is with the substring "abc". There is no match in the string "Grab crab" because while it contains the substring "ab c", it does not contain the exact substring "abc".

Using special characters

When the search for a match requires something more than a direct match, such as finding one or more b's, or finding white space, you can include special characters in the pattern. For example, to match a single "a" followed by zero or more "b"s followed by "c", you'd use the pattern /ab*c/: the * after "b" means "0 or more occurrences of the preceding item." In the string "cbbabbbbcdebc", this pattern will match the substring "abbbbc".

The following pages provide lists of the different special characters that fit into each category, along with descriptions and examples.

Assertions
Assertions include boundaries, which indicate the beginnings and endings of lines and words, and other patterns indicating in some way that a match is possible (including look-ahead, look-behind, and conditional expressions).
Character classes
Distinguish different types of characters. For example, distinguishing between letters and digits.
Groups and ranges
Indicate groups and ranges of expression characters.
Quantifiers
Indicate numbers of characters or expressions to match.
Unicode property escapes
Distinguish based on unicode character properties, for example, upper- and lower-case letters, math symbols, and punctuation.

If you want to look at all the special characters that can be used in regular expressions in a single table, see the following:

Special characters in regular expressions.
Characters / constructs Corresponding article
\, ., \cX, \d, \D, \f, \n, \r, \s, \S, \t, \v, \w, \W, \0, \xhh, \uhhhh, \uhhhhh, [\b]

Character classes

^, $, x(?=y), x(?!y), (?<=y)x, (?<!y)x, \b, \B

Assertions

(x), (?:x), (?<Name>x)x|y, [xyz], [^xyz], \Number

Groups and ranges

*, +, ?, x{n}, x{n,}, x{n,m}

Quantifiers

\p{UnicodeProperty}, \P{UnicodeProperty} Unicode property escapes

Note: A larger cheatsheet is also available (only aggregating parts of those individual articles).

Escaping

If you need to use any of the special characters literally (actually searching for a "*", for instance), you must escape it by putting a backslash in front of it. For instance, to search for "a" followed by "*" followed by "b", you'd use /a\*b/ — the backslash "escapes" the "*", making it literal instead of special.

Similarly, if you're writing a regular expression literal and need to match a slash ("/"), you need to escape that (otherwise, it terminates the pattern). For instance, to search for the string "/example/" followed by one or more alphabetic characters, you'd use /\/example\/[a-z]+/i—the backslashes before each slash make them literal.

To match a literal backslash, you need to escape the backslash. For instance, to match the string "C:\" where "C" can be any letter, you'd use /[A-Z]:\\/ — the first backslash escapes the one after it, so the expression searches for a single literal backslash.

If using the RegExp constructor with a string literal, remember that the backslash is an escape in string literals, so to use it in the regular expression, you need to escape it at the string literal level. /a\*b/ and new RegExp("a\\*b") create the same expression, which searches for "a" followed by a literal "*" followed by "b".

If escape strings are not already part of your pattern you can add them using String.replace:

function escapeRegExp(string) {
  return string.replace(/[.*+\-?^${}()|[\]\\]/g, '\\$&'); // $& means the whole matched string
}

The "g" after the regular expression is an option or flag that performs a global search, looking in the whole string and returning all matches. It is explained in detail below in Advanced Searching With Flags.

Why isn't this built into JavaScript? There is a proposal to add such a function to RegExp, but it was rejected by TC39.

Using parentheses

Parentheses around any part of the regular expression pattern causes that part of the matched substring to be remembered. Once remembered, the substring can be recalled for other use. See Groups and ranges for more details.

Using regular expressions in JavaScript

Regular expressions are used with the RegExp methods test() and exec() and with the String methods match(), replace(), search(), and split(). These methods are explained in detail in the JavaScript reference.

Methods that use regular expressions
Method Description
exec() Executes a search for a match in a string. It returns an array of information or null on a mismatch.
test() Tests for a match in a string. It returns true or false.
match() Returns an array containing all of the matches, including capturing groups, or null if no match is found.
matchAll() Returns an iterator containing all of the matches, including capturing groups.
search() Tests for a match in a string. It returns the index of the match, or -1 if the search fails.
replace() Executes a search for a match in a string, and replaces the matched substring with a replacement substring.
replaceAll() Executes a search for all matches in a string, and replaces the matched substrings with a replacement substring.
split() Uses a regular expression or a fixed string to break a string into an array of substrings.

When you want to know whether a pattern is found in a string, use the test() or search() methods; for more information (but slower execution) use the exec() or match() methods. If you use exec() or match() and if the match succeeds, these methods return an array and update properties of the associated regular expression object and also of the predefined regular expression object, RegExp. If the match fails, the exec() method returns null (which coerces to false).

In the following example, the script uses the exec() method to find a match in a string.

var myRe = /d(b+)d/g;
var myArray = myRe.exec('cdbbdbsbz');

If you do not need to access the properties of the regular expression, an alternative way of creating myArray is with this script:

var myArray = /d(b+)d/g.exec('cdbbdbsbz'); 
    // similar to "cdbbdbsbz".match(/d(b+)d/g); however,
    // "cdbbdbsbz".match(/d(b+)d/g) outputs Array [ "dbbd" ], while 
    // /d(b+)d/g.exec('cdbbdbsbz') outputs Array [ 'dbbd', 'bb', index: 1, input: 'cdbbdbsbz' ].

(See different behaviors for further info about the different behaviors.)

If you want to construct the regular expression from a string, yet another alternative is this script:

var myRe = new RegExp('d(b+)d', 'g');
var myArray = myRe.exec('cdbbdbsbz');

With these scripts, the match succeeds and returns the array and updates the properties shown in the following table.

Results of regular expression execution.
Object Property or index Description In this example
myArray The matched string and all remembered substrings. ['dbbd', 'bb', index: 1, input: 'cdbbdbsbz']
index The 0-based index of the match in the input string. 1
input The original string. 'cdbbdbsbz'
[0] The last matched characters. 'dbbd'
myRe lastIndex The index at which to start the next match. (This property is set only if the regular expression uses the g option, described in Advanced Searching With Flags.) 5
source The text of the pattern. Updated at the time that the regular expression is created, not executed. 'd(b+)d'

As shown in the second form of this example, you can use a regular expression created with an object initializer without assigning it to a variable. If you do, however, every occurrence is a new regular expression. For this reason, if you use this form without assigning it to a variable, you cannot subsequently access the properties of that regular expression. For example, assume you have this script:

var myRe = /d(b+)d/g;
var myArray = myRe.exec('cdbbdbsbz');
console.log('The value of lastIndex is ' + myRe.lastIndex);

// "The value of lastIndex is 5"

However, if you have this script:

var myArray = /d(b+)d/g.exec('cdbbdbsbz');
console.log('The value of lastIndex is ' + /d(b+)d/g.lastIndex);

// "The value of lastIndex is 0"

The occurrences of /d(b+)d/g in the two statements are different regular expression objects and hence have different values for their lastIndex property. If you need to access the properties of a regular expression created with an object initializer, you should first assign it to a variable.

Advanced searching with flags

Regular expressions have six optional flags that allow for functionality like global and case insensitive searching. These flags can be used separately or together in any order, and are included as part of the regular expression.

Regular expression flags
Flag Description Corresponding property
g Global search. RegExp.prototype.global
i Case-insensitive search. RegExp.prototype.ignoreCase
m Multi-line search. RegExp.prototype.multiline
s Allows . to match newline characters. RegExp.prototype.dotAll
u "unicode"; treat a pattern as a sequence of unicode code points. RegExp.prototype.unicode
y Perform a "sticky" search that matches starting at the current position in the target string. See sticky. RegExp.prototype.sticky

To include a flag with the regular expression, use this syntax:

var re = /pattern/flags;

or

var re = new RegExp('pattern', 'flags');

Note that the flags are an integral part of a regular expression. They cannot be added or removed later.

For example, re = /\w+\s/g creates a regular expression that looks for one or more characters followed by a space, and it looks for this combination throughout the string.

var re = /\w+\s/g;
var str = 'fee fi fo fum';
var myArray = str.match(re);
console.log(myArray);

// ["fee ", "fi ", "fo "]

You could replace the line:

var re = /\w+\s/g;

with:

var re = new RegExp('\\w+\\s', 'g');

and get the same result.

The behavior associated with the g flag is different when the .exec() method is used.  The roles of "class" and "argument" get reversed: In the case of .match(), the string class (or data type) owns the method and the regular expression is just an argument, while in the case of .exec(), it is the regular expression that owns the method, with the string being the argument.  Contrast this str.match(re) versus re.exec(str).  The g flag is used with the .exec() method to get iterative progression.

var xArray; while(xArray = re.exec(str)) console.log(xArray);
// produces: 
// ["fee ", index: 0, input: "fee fi fo fum"]
// ["fi ", index: 4, input: "fee fi fo fum"]
// ["fo ", index: 7, input: "fee fi fo fum"]

The m flag is used to specify that a multiline input string should be treated as multiple lines. If the m flag is used, ^ and $ match at the start or end of any line within the input string instead of the start or end of the entire string.

Examples

Note: Several examples are also available in:

Using special characters to verify input

In the following example, the user is expected to enter a phone number. When the user presses the "Check" button, the script checks the validity of the number. If the number is valid (matches the character sequence specified by the regular expression), the script shows a message thanking the user and confirming the number. If the number is invalid, the script informs the user that the phone number is not valid.

Within non-capturing parentheses (?: , the regular expression looks for three numeric characters \d{3} OR | a left parenthesis \( followed by three digits \d{3}, followed by a close parenthesis \), (end non-capturing parenthesis )), followed by one dash, forward slash, or decimal point and when found, remember the character ([-\/\.]), followed by three digits \d{3}, followed by the remembered match of a dash, forward slash, or decimal point \1, followed by four digits \d{4}.

The Change event activated when the user presses Enter sets the value of RegExp.input.

HTML

<p>
  Enter your phone number (with area code) and then click "Check".
  <br>
  The expected format is like ###-###-####.
</p>
<form action="#">
  <input id="phone">
    <button onclick="testInfo(document.getElementById('phone'));">Check</button>
</form>

JavaScript

var re = /(?:\d{3}|\(\d{3}\))([-\/\.])\d{3}\1\d{4}/;
function testInfo(phoneInput) {
  var OK = re.exec(phoneInput.value);
  if (!OK) {
    console.error(phoneInput.value + ' isn\'t a phone number with area code!'); 
  } else {
    console.log('Thanks, your phone number is ' + OK[0]);}
} 

Result

Tools

RegExr
An online tool to learn, build, & test Regular Expressions.
Regex tester
An online regex builder/debugger
Regex visualizer
An online visual regex tester.

Specifications

Specification
ECMAScript (ECMA-262)
The definition of 'RegExp' in that specification.

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
RegExpChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp() constructorChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
compile
Deprecated
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 6Safari Full support 3.1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 2Samsung Internet Android Full support 1.0nodejs Full support Yes
dotAllChrome Full support 62Edge Full support 79Firefox Full support 78IE No support NoOpera Full support 49Safari Full support 12WebView Android Full support 62Chrome Android Full support 62Firefox Android No support NoOpera Android Full support 46Safari iOS Full support 12Samsung Internet Android Full support 8.0nodejs 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 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
flagsChrome Full support 49Edge Full support 79Firefox Full support 37IE No support NoOpera Full support 39Safari Full support 9WebView Android Full support 49Chrome Android Full support 49Firefox Android Full support 37Opera Android Full support 41Safari iOS Full support 9Samsung Internet Android Full support 5.0nodejs Full support 6.0.0
globalChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
ignoreCaseChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.input ($_)
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 15Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 14Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
lastIndexChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.lastMatch ($&)
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 10.5Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 11Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.lastParen ($+)
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 10.5Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 11Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.leftContext ($`)
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 8Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
lookbehind assertions ((?<= ) and (?<! ))Chrome Full support 62Edge Full support 79Firefox Full support 78IE No support NoOpera Full support 49Safari No support NoWebView Android Full support 62Chrome Android Full support 62Firefox 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 8.0nodejs Full support 8.10.0
multilineChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.$1-$9Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
Named capture groupsChrome Full support 64Edge Full support 79Firefox Full support 78IE No support NoOpera Full support 51Safari Full support 11.1WebView Android Full support 64Chrome Android Full support 64Firefox Android No support NoOpera Android Full support 47Safari iOS Full support 11.3Samsung Internet Android Full support 9.0nodejs Full support 10.0.0
Full support 10.0.0
Full support 8.3.0
Disabled
Disabled From version 8.3.0: this feature is behind the --harmony runtime flag.
Unicode property escapes (\p{...})Chrome Full support 64Edge Full support 79Firefox Full support 78IE No support NoOpera Full support 51Safari Full support 11.1WebView Android Full support 64Chrome Android Full support 64Firefox Android No support NoOpera Android Full support 47Safari iOS Full support 11.3Samsung Internet Android Full support 9.0nodejs Full support 10.0.0
Full support 10.0.0
Full support 8.3.0
Disabled
Disabled From version 8.3.0: this feature is behind the --harmony runtime flag.
RegExp.rightContext ($')
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 8Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
sourceChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs 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 49Firefox Android Full support 4Opera Android Full support 36Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support Yes
testChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
toSource
Non-standard
Chrome No support NoEdge No support NoFirefox No support 1 — 74
Notes
No support 1 — 74
Notes
Notes Starting in Firefox 74, toSource() is no longer available for use by web content. It is still allowed for internal and privileged code.
IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android 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 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs 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 50Chrome Android Full support 50Firefox Android Full support 46Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support Yes
@@matchChrome Full support 50Edge Full support 13Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0
@@matchAllChrome Full support 73Edge Full support 79Firefox Full support 67IE No support NoOpera Full support 60Safari Full support 13WebView Android Full support 73Chrome Android Full support 73Firefox Android Full support 67Opera Android Full support 52Safari iOS Full support 13Samsung Internet Android Full support 5.0nodejs Full support 12.0.0
@@replaceChrome Full support 50Edge Full support 79Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0
@@searchChrome Full support 50Edge Full support 13Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0
@@speciesChrome Full support 50Edge Full support 13Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs 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 50Edge Full support 79Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs 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.

Document Tags and Contributors

Last updated by: pixelscript,