XRegExp provides augmented, extensible, cross-browser JavaScript regular expressions. You get new syntax and flags beyond what browsers support natively, along with a collection of utils to make your client-side grepping and parsing easier. XRegExp also frees you from worrying about pesky inconsistencies in cross-browser regex handling and the dubious lastIndex property.

XRegExp supports all native ES5 regular expression syntax. It’s about 3.5 KB when minified and gzipped. It works with Internet Explorer 5.5+, Firefox 1.5+, Chrome, Safari 3+, and Opera 9.5+.


XRegExp regular expressions compile to native RegExp objects, thus there is no performance difference when using XRegExp objects with native methods. There is a small performance cost when compiling XRegExps. If you want, however, you can use XRegExp.cache to avoid ever incurring the compilation cost for a given pattern more than once. Doing so can even lead to XRegExp being faster than native regexes in synthetic tests that repeatedly compile the same regex.

Usage examples

// Using named capture and flag x (free-spacing and line comments)
var date = XRegExp('(?<year>  [0-9]{4}) -?  # year  \n\
                    (?<month> [0-9]{2}) -?  # month \n\
                    (?<day>   [0-9]{2})     # day   ', 'x');

// XRegExp.exec gives you named backreferences on the match result
var match = XRegExp.exec('2012-02-22', date);
match.day; // -> '22'

// It also includes optional pos and sticky arguments
var pos = 3, result = [];
while (match = XRegExp.exec('<1><2><3><4>5<6>', /<(\d+)>/, pos, 'sticky')) {
    pos = match.index + match[0].length;
} // result -> ['2', '3', '4']

// XRegExp.replace allows named backreferences in replacements
XRegExp.replace('2012-02-22', date, '${month}/${day}/${year}'); // -> '02/22/2012'
XRegExp.replace('2012-02-22', date, function (match) {
    return match.month + '/' + match.day + '/' + match.year;
}); // -> '02/22/2012'

// In fact, all XRegExps are RegExps and work perfectly with native methods
date.test('2012-02-22'); // -> true

// The *only* caveat is that named captures must be referred to using numbered backreferences
'2012-02-22'.replace(date, '$2/$3/$1'); // -> '02/22/2012'

// If you want, you can extend native methods so you don't have to worry about this
// Doing so also fixes numerous browser bugs in the native methods
'2012-02-22'.replace(date, '${month}/${day}/${year}'); // -> '02/22/2012'
'2012-02-22'.replace(date, function (match) {
    return match.month + '/' + match.day + '/' + match.year;
}); // -> '02/22/2012'
date.exec('2012-02-22').day; // -> '22'

// Extract every other digit from a string using XRegExp.forEach
XRegExp.forEach('1a2345', /\d/, function (match, i) {
    if (i % 2) this.push(+match[0]);
}, []); // -> [2, 4]

// Get numbers within <b> tags using XRegExp.matchChain
XRegExp.matchChain('1 <b>2</b> 3 <b>4 a 56</b>', [
]); // -> ['2', '4', '56']

// You can also pass forward and return specific backreferences
var html = '<a href="http://xregexp.com/">XRegExp</a>\
            <a href="http://www.google.com/">Google</a>';
XRegExp.matchChain(html, [
    {regex: /<a href="([^"]+)">/i, backref: 1},
    {regex: XRegExp('(?i)^https?://(?<domain>[^/?#]+)'), backref: 'domain'}
]); // -> ['xregexp.com', 'www.google.com']

// XRegExp.union safely merges strings and regexes into a single pattern
XRegExp.union(['a+b*c', /(dogs)\1/, /(cats)\1/], 'i');
// -> /a\+b\*c|(dogs)\1|(cats)\2/i

These examples should give you the flavor of what’s possible, but XRegExp has more syntax, flags, utils, options, and browser fixes that aren’t shown here. You can even augment XRegExp’s regular expression syntax with addons (see below) or write your own. See xregexp.com for more details.


In browsers, you can either load addons individually, or bundle all addons together with XRegExp by loading xregexp-all.js. XRegExp’s npm package uses xregexp-all.js, which means that the addons are always available when XRegExp is installed on the server using npm.

XRegExp Unicode Base

In browsers, first include the Unicode Base script:

<script src="xregexp.js"></script>
<script src="addons/unicode/unicode-base.js"></script>

Then you can do this:

var unicodeWord = XRegExp('^\\p{L}+$');
unicodeWord.test('Русский'); // -> true
unicodeWord.test('日本語'); // -> true
unicodeWord.test('العربية'); // -> true

The base script adds \p{Letter} and its alias \p{L}, but other Unicode categories, scripts, blocks, and properties require addon packages. Try these next examples after additionally including unicode-scripts.js:

XRegExp('^\\p{Hiragana}+$').test('ひらがな'); // -> true
XRegExp('^[\\p{Latin}\\p{Common}]+$').test('Über Café.'); // -> true

XRegExp uses the Unicode 6.1 Basic Multilingual Plane.


In browsers, first include the script:

<script src="xregexp.js"></script>
<script src="addons/build.js"></script>

You can then build regular expressions using named subpatterns, for readability and pattern reuse:

var time = XRegExp.build('(?x)^  () $', {
    hours: XRegExp.build(' : | ', {
        h12: /1[0-2]|0?[1-9]/,
        h24: /2[0-3]|[01][0-9]/
    }, 'x'),
    minutes: /^[0-5][0-9]$/

time.test('10:59'); // -> true
XRegExp.exec('10:59', time).minutes; // -> '59'

Named subpatterns can be provided as strings or regex objects. A leading ^ and trailing unescaped $ are stripped from subpatterns if both are present, which allows embedding independently useful anchored patterns. `` tokens can be quantified as a single unit. Backreferences in the outer pattern and provided subpatterns are automatically renumbered to work correctly within the larger combined pattern. The syntax () works as shorthand for named capture via (?<name>). Named subpatterns cannot be embedded within character classes.

See also: Creating Grammatical Regexes Using XRegExp.build.


In browsers, first include the script:

<script src="xregexp.js"></script>
<script src="addons/matchrecursive.js"></script>

You can then match recursive constructs using XRegExp pattern strings as left and right delimiters:

var str = '(t((e))s)t()(ing)';
XRegExp.matchRecursive(str, '\\(', '\\)', 'g');
// -> ['t((e))s', '', 'ing']

// Extended information mode with valueNames
str = 'Here is <div> <div>an</div></div> example';
XRegExp.matchRecursive(str, '<div\\s*>', '</div>', 'gi', {
    valueNames: ['between', 'left', 'match', 'right']
/* -> [
{name: 'between', value: 'Here is ',       start: 0,  end: 8},
{name: 'left',    value: '<div>',          start: 8,  end: 13},
{name: 'match',   value: ' <div>an</div>', start: 13, end: 27},
{name: 'right',   value: '</div>',         start: 27, end: 33},
{name: 'between', value: ' example',       start: 33, end: 41}
] */

// Omitting unneeded parts with null valueNames, and using escapeChar
str = '...{1}\\';
XRegExp.matchRecursive(str, '{', '}', 'g', {
    valueNames: ['literal', null, 'value', null],
    escapeChar: '\\'
/* -> [
{name: 'literal', value: '...', start: 0, end: 3},
{name: 'value',   value: '1',   start: 4, end: 5},
{name: 'literal', value: '\\{', start: 6, end: 8},
{name: 'value',   value: 'function(x,y){return y+x;}', start: 9, end: 35}
] */

// Sticky mode via flag y
str = '<1><<<2>>><3>4<5>';
XRegExp.matchRecursive(str, '<', '>', 'gy');
// -> ['1', '<<2>>', '3']

XRegExp.matchRecursive throws an error if it sees an unbalanced delimiter in the target string.

XRegExp Prototype Methods

In browsers, first include the script:

<script src="xregexp.js"></script>
<script src="addons/prototypes.js"></script>

New XRegExp regexes then gain a collection of useful methods: apply, call, forEach, globalize, xexec, and xtest.

// To demonstrate the call method, let's first create the function we'll be using...
function filter(array, fn) {
    var res = [];
    array.forEach(function (el) {if (fn.call(null, el)) res.push(el);});
    return res;
// Now we can filter arrays using functions and regexes
filter(['a', 'ba', 'ab', 'b'], XRegExp('^a')); // -> ['a', 'ab']

Native RegExp objects copied by XRegExp are augmented with any XRegExp.prototype methods. The following lines therefore work equivalently:

XRegExp('[a-z]', 'ig').xexec('abc');

Installation and usage

In browsers:

<script src="xregexp-min.js"></script>

Or, to bundle XRegExp with all of its addons:

<script src="xregexp-all-min.js"></script>

Using npm:

npm install xregexp

In Node.js and CommonJS module loaders:

var XRegExp = require('xregexp').XRegExp;

Running tests on the server with npm

npm install -g qunit  # needed to run the tests
npm test  # in the xregexp root

If XRegExp was not installed using npm, just open tests/index.html in your browser.


Lookbehind: A collection of short functions is available that makes it easy to simulate infinite-length leading lookbehind.



XRegExp and addons copyright 2007-2012 by Steven Levithan.

Tools: Unicode range generators by Mathias Bynens. Source file concatenator by Bjarke Walling.

Prior art: XRegExp.build inspired by Lea Verou’s RegExp.create. XRegExp.union inspired by Ruby. XRegExp’s syntax extensions come from Perl, .NET, etc.

All code released under the MIT License.

Fork me to show support, fix, and extend.