The definitive source of the best
JavaScript libraries, frameworks, and plugins.

  • ×

    Extended JavaScript regular expressions
    Filed under  › 

    • 🔾62%Overall
    • 3,239
    • 19.6 days
    • 🕩276
    • 👥9

    XRegExp 5.1.1

    Build Status

    XRegExp provides augmented (and extensible) JavaScript regular expressions. You get modern syntax and flags beyond what browsers support natively. XRegExp is also a regex utility belt with tools to make your grepping and parsing easier, while freeing you from regex cross-browser inconsistencies and other annoyances.

    XRegExp supports all native ES6 regular expression syntax. It supports ES5+ browsers, and you can use it with Node.js or as a RequireJS module. Over the years, many of XRegExp's features have been adopted by new JavaScript standards (named capturing, Unicode properties/scripts/categories, flag s, sticky matching, etc.), so using XRegExp can be a way to extend these features into older browsers.


    XRegExp compiles to native RegExp objects. Therefore regexes built with XRegExp perform just as fast as native regular expressions. There is a tiny extra cost when compiling a pattern for the first time.

    Named capture breaking change in XRegExp 5

    XRegExp 5 introduced a breaking change where named backreference properties now appear on the result's groups object (following ES2018), rather than directly on the result. To restore the old handling so you don't need to update old code, run the following line after importing XRegExp:


    XRegExp 4.1.0 and later allow introducing the new behavior without upgrading to XRegExp 5 by running XRegExp.install('namespacing').

    Following is the most commonly needed change to update code for the new behavior:

    // Change this
    const name = XRegExp.exec(str, regexWithNamedCapture).name;
    // To this
    const name = XRegExp.exec(str, regexWithNamedCapture);

    See below for more examples of using named capture with XRegExp.exec and XRegExp.replace.

    Usage examples

    // Using named capture and flag x for free-spacing and line comments
    const date = XRegExp(
        `(?<year>  [0-9]{4} ) -?  # year
         (?<month> [0-9]{2} ) -?  # month
         (?<day>   [0-9]{2} )     # day`, 'x');
    // XRegExp.exec provides named backreferences on the result's groups property
    let match = XRegExp.exec('2021-02-22', date);
    match.groups.year; // -> '2021'
    // It also includes optional pos and sticky arguments
    let pos = 3;
    const result = [];
    while (match = XRegExp.exec('<1><2><3>4<5>', /<(\d+)>/, pos, 'sticky')) {
        pos = match.index + match[0].length;
    // result -> ['2', '3']
    // XRegExp.replace allows named backreferences in replacements
    XRegExp.replace('2021-02-22', date, '$<month>/$<day>/$<year>');
    // -> '02/22/2021'
    XRegExp.replace('2021-02-22', date, (...args) => {
        // Named backreferences are on the last argument
        const groups = args[args.length - 1];
        return `${groups.month}/${}/${groups.year}`;
    // -> '02/22/2021'
    // XRegExps compile to RegExps and work with native methods
    // -> true
    // However, named captures must be referenced using numbered backreferences
    // if used with native methods
    '2021-02-22'.replace(date, '$2/$3/$1');
    // -> '02/22/2021'
    // Use XRegExp.forEach to extract every other digit from a string
    const evens = [];
    XRegExp.forEach('1a2345', /\d/, (match, i) => {
        if (i % 2) evens.push(+match[0]);
    // evens -> [2, 4]
    // Use XRegExp.matchChain to get numbers within <b> tags
    XRegExp.matchChain('1 <b>2</b> 3 <B>4 \n 56</B>', [
        XRegExp('<b>.*?</b>', 'is'),
    // -> ['2', '4', '56']
    // You can also pass forward and return specific backreferences
    const html =
        `<a href="">XRegExp</a>
         <a href="">Google</a>`;
    XRegExp.matchChain(html, [
        {regex: /<a href="([^"]+)">/i, backref: 1},
        {regex: XRegExp('(?i)^https?://(?<domain>[^/?#]+)'), backref: 'domain'}
    // -> ['', '']
    // Merge strings and regexes, with updated backreferences
    XRegExp.union(['m+a*n', /(bear)\1/, /(pig)\1/], 'i', {conjunction: 'or'});
    // -> /m\+a\*n|(bear)\1|(pig)\2/i

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


    You can either load addons individually, or bundle all addons with XRegExp by loading xregexp-all.js from


    If not using xregexp-all.js, first include the Unicode Base script and then one or more of the addons for Unicode categories, properties, or scripts.

    Then you can do this:

    // Test some Unicode scripts
    // Can also use the Script= prefix to match ES2018: \p{Script=Hiragana}
    XRegExp('^\\p{Hiragana}+$').test('ひらがな'); // -> true
    XRegExp('^[\\p{Latin}\\p{Common}]+$').test('Über Café.'); // -> true
    // Test the Unicode categories Letter and Mark
    // Can also use the short names \p{L} and \p{M}
    const unicodeWord = XRegExp.tag()`^\p{Letter}[\p{Letter}\p{Mark}]*$`;
    unicodeWord.test('Русский'); // -> true
    unicodeWord.test('日本語'); // -> true
    unicodeWord.test('العربية'); // -> true

    By default, \p{…} and \P{…} support the Basic Multilingual Plane (i.e. code points up to U+FFFF). You can opt-in to full 21-bit Unicode support (with code points up to U+10FFFF) on a per-regex basis by using flag A. This is called astral mode. You can automatically add flag A for all new regexes by running XRegExp.install('astral'). When in astral mode, \p{…} and \P{…} always match a full code point rather than a code unit, using surrogate pairs for code points above U+FFFF.

    // Using flag A to match astral code points
    XRegExp('^\\p{S}$').test('💩'); // -> false
    XRegExp('^\\p{S}$', 'A').test('💩'); // -> true
    // Using surrogate pair U+D83D U+DCA9 to represent U+1F4A9 (pile of poo)
    XRegExp('^\\p{S}$', 'A').test('\uD83D\uDCA9'); // -> true
    // Implicit flag A
    XRegExp('^\\p{S}$').test('💩'); // -> true

    Opting in to astral mode disables the use of \p{…} and \P{…} within character classes. In astral mode, use e.g. (\pL|[0-9_])+ instead of [\pL0-9_]+.

    XRegExp uses Unicode 14.0.0.

    Build regular expressions using named subpatterns, for readability and pattern reuse:

    const time ='(?x)^ {{hours}} ({{minutes}}) $', {
        hours:'{{h12}} : | {{h24}}', {
            h12: /1[0-2]|0?[1-9]/,
            h24: /2[0-3]|[01][0-9]/
        minutes: /^[0-5][0-9]$/
    time.test('10:59'); // -> true
    XRegExp.exec('10:59', time).groups.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. Any backreferences in the outer pattern or provided subpatterns are automatically renumbered to work correctly within the larger combined pattern. The syntax ({{name}}) works as shorthand for named capture via (?<name>{{name}}). Named subpatterns cannot be embedded within character classes.

    XRegExp.tag (included with

    Provides tagged template literals that create regexes with XRegExp syntax and flags:

    XRegExp.tag()`\b\w+\b`.test('word'); // -> true
    const hours = /1[0-2]|0?[1-9]/;
    const minutes = /(?<minutes>[0-5][0-9])/;
    const time = XRegExp.tag('x')`\b ${hours} : ${minutes} \b`;
    time.test('10:59'); // -> true
    XRegExp.exec('10:59', time).groups.minutes; // -> '59'
    const backref1 = /(a)\1/;
    const backref2 = /(b)\1/;
    XRegExp.tag()`${backref1}${backref2}`.test('aabb'); // -> true

    XRegExp.tag does more than just interpolation. You get all the XRegExp syntax and flags, and since it reads patterns as raw strings, you no longer need to escape all your backslashes. XRegExp.tag also uses under the hood, so you get all of its extras for free. Leading ^ and trailing unescaped $ are stripped from interpolated patterns if both are present (to allow embedding independently useful anchored regexes), interpolating into a character class is an error (to avoid unintended meaning in edge cases), interpolated patterns are treated as atomic units when quantified, interpolated strings have their special characters escaped, and any backreferences within an interpolated regex are rewritten to work within the overall pattern.


    A robust and flexible API for matching recursive constructs using XRegExp pattern strings as left and right delimiters:

    const str1 = '(t((e))s)t()(ing)';
    XRegExp.matchRecursive(str1, '\\(', '\\)', 'g');
    // -> ['t((e))s', '', 'ing']
    // Extended information mode with valueNames
    const str2 = 'Here is <div> <div>an</div></div> example';
    XRegExp.matchRecursive(str2, '<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
    const str3 = '...{1}.\\{{function(x,y){return {y:x}}}';
    XRegExp.matchRecursive(str3, '{', '}', '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: 9},
    {name: 'value',   value: 'function(x,y){return {y:x}}', start: 10, end: 37}
    ] */
    // Sticky mode via flag y
    const str4 = '<1><<<2>>><3>4<5>';
    XRegExp.matchRecursive(str4, '<', '>', 'gy');
    // -> ['1', '<<2>>', '3']
    // Skipping unbalanced delimiters instead of erroring
    const str5 = 'Here is <div> <div>an</div> unbalanced example';
    XRegExp.matchRecursive(str5, '<div\\s*>', '</div>', 'gi', {
        unbalanced: 'skip'
    // -> ['an']

    By default, XRegExp.matchRecursive throws an error if it scans past an unbalanced delimiter in the target string. Multiple alternative options are available for handling unbalanced delimiters.

    Installation and usage

    In browsers (bundle XRegExp with all of its addons):

    <script src=""></script>

    Using npm:

    npm install xregexp

    In Node.js:

    const XRegExp = require('xregexp');

    Contribution guide

    1. Fork the repository and clone the forked version locally.
    2. Ensure you have the typescript module installed globally.
    3. Run npm install.
    4. Ensure all tests pass with npm test.
    5. Add tests for new functionality or that fail from the bug not fixed.
    6. Implement functionality or bug fix to pass the test.


    XRegExp project collaborators are:

    Thanks to all contributors and others who have submitted code, provided feedback, reported bugs, and inspired new features.

    XRegExp is released under the MIT License. Learn more at

    Show All