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JS regexes + future

Regular Expressions Cookbook (book cover)

“Regular Expressions Cookbook manages to be simultaneously accessible and almost ridiculously comprehensive.”
—Jeff Atwood

API

XRegExp(pattern, [flags])

Creates an extended regular expression object for matching text with a pattern. Differs from a native regular expression in that additional syntax and flags are supported. The returned object is in fact a native RegExp and works with all native methods.

Parameters:
  • pattern {String|RegExp}
    Regex pattern string, or an existing regex object to copy.
  • [flags] {String}
    Any combination of flags.
    Native flags:
    • g - global
    • i - ignore case
    • m - multiline anchors
    • u - unicode (ES6)
    • y - sticky (Firefox 3+, ES6)
    Additional XRegExp flags:
    • n - explicit capture
    • s - dot matches all (aka singleline) - works even when not natively supported
    • x - free-spacing and line comments (aka extended)
    • A - astral (requires the Unicode Base addon)
    Flags cannot be provided when constructing one RegExp from another.
Returns: {RegExp}
Extended regular expression object.

Example

// With named capture and flag x
XRegExp(`(?<year>  [0-9]{4} ) [-\\s]?  # year
         (?<month> [0-9]{2} ) [-\\s]?  # month
         (?<day>   [0-9]{2} )          # day`, 'x');

// Providing a regex object copies it. Native regexes are recompiled using native (not
// XRegExp) syntax. Copies maintain extended data, are augmented with `XRegExp.prototype`
// properties, and have fresh `lastIndex` properties (set to zero).
XRegExp(/regex/);

For details about the regular expression just shown, see Syntax: Named capture and Flags: Free-spacing.

Regexes, strings, and backslashes

JavaScript string literals (as opposed to, e.g., user input or text extracted from the DOM) use a backslash as an escape character. The string literal '\\' therefore contains a single backslash, and its length property's value is 1. However, a backslash is also an escape character in regular expression syntax, where the pattern \\ matches a single backslash. When providing string literals to the RegExp or XRegExp constructor functions, four backslashes are therefore needed to match a single backslash—e.g., XRegExp('\\\\'). Only two of those backslashes are actually passed into the constructor function. The other two are used to escape the backslashes in the string before the function ever sees the string. The exception is when using ES6 raw strings via String.raw or XRegExp.tag.

The same issue is at play with the \\s sequences in the example code just shown. XRegExp is provided with the two characters \s, which it in turn recognizes as the metasequence used to match a whitespace character.

XRegExp.addToken(regex, handler, [options])

Extends XRegExp syntax and allows custom flags. This is used internally and can be used to create XRegExp addons. If more than one token can match the same string, the last added wins.

Parameters:
  • regex {RegExp}
    Regex object that matches the new token.
  • handler {Function}
    Function that returns a new pattern string (using native regex syntax) to replace the matched token within all future XRegExp regexes. Has access to persistent properties of the regex being built, through this. Invoked with three arguments:
    1. The match array, with named backreference properties.
    2. The regex scope where the match was found: 'default' or 'class'.
    3. The flags used by the regex, including any flags in a leading mode modifier.
    The handler function becomes part of the XRegExp construction process, so be careful not to construct XRegExps within the function or you will trigger infinite recursion.
  • [options] {Object}
    Options object with optional properties:
    • scope {String} Scopes where the token applies: 'default', 'class', or 'all'.
    • flag {String} Single-character flag that triggers the token. This also registers the flag, which prevents XRegExp from throwing an 'unknown flag' error when the flag is used.
    • optionalFlags {String} Any custom flags checked for within the token handler that are not required to trigger the token. This registers the flags, to prevent XRegExp from throwing an 'unknown flag' error when any of the flags are used.
    • reparse {Boolean} Whether the handler function's output should not be treated as final, and instead be reparseable by other tokens (including the current token). Allows token chaining or deferring.
    • leadChar {String} Single character that occurs at the beginning of any successful match of the token (not always applicable). This doesn't change the behavior of the token unless you provide an erroneous value. However, providing it can increase the token's performance since the token can be skipped at any positions where this character doesn't appear.
Returns: {undefined}
Does not return a value.

Example

// Basic usage: Add \a for the ALERT control code
XRegExp.addToken(
  /\\a/,
  () => '\\x07',
  {scope: 'all'}
);
XRegExp('\\a[\\a-\\n]+').test('\x07\n\x07'); // -> true

Show more XRegExp.addToken examples. ↓

XRegExp.build(pattern, subs, [flags])

Requires the XRegExp.build addon, which is bundled in xregexp-all.js.

Builds regexes using named subpatterns, for readability and pattern reuse. Backreferences in the outer pattern and provided subpatterns are automatically renumbered to work correctly. Native flags used by provided subpatterns are ignored in favor of the flags argument.

Parameters:
  • pattern {String}
    XRegExp pattern using {{name}} for embedded subpatterns. Allows ({{name}}) as shorthand for (?<name>{{name}}). Patterns cannot be embedded within character classes.
  • subs {Object}
    Lookup object for named subpatterns. Values can be strings or regexes. A leading ^ and trailing unescaped $ are stripped from subpatterns, if both are present.
  • [flags] {String}
    Any combination of XRegExp flags.
Returns:
  • {RegExp}
    Regex with interpolated subpatterns.

Example

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

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

See also: Creating Grammatical Regexes Using XRegExp.build.

XRegExp.cache(pattern, [flags])

Caches and returns the result of calling XRegExp(pattern, flags). On any subsequent call with the same pattern and flag combination, the cached copy of the regex is returned.

Parameters:
  • pattern {String}
    Regex pattern string.
  • [flags] {String}
    Any combination of XRegExp flags.
Returns: {RegExp}
Cached XRegExp object.

Example

let match;
while (match = XRegExp.cache('.', 'gs').exec('abc')) {
  // The regex is compiled once only
}

const regex1 = XRegExp.cache('.', 's'),
const regex2 = XRegExp.cache('.', 's');
// regex1 and regex2 are references to the same regex object

XRegExp.escape(str)

Escapes any regular expression metacharacters, for use when matching literal strings. The result can safely be used at any position within a regex that uses any flags.

The escaped characters are [, ], {, }, (, ), -, *, +, ?, ., \, ^, $, |, ,, #, and whitespace (see free-spacing for the list of whitespace characters).

Parameters:
  • str {String}
    String to escape.
Returns: {String}
String with regex metacharacters escaped.

Example

XRegExp.escape('Escaped? <.>');
// -> 'Escaped\?\u0020<\.>'

XRegExp.exec(str, regex, [pos], [sticky])

Executes a regex search in a specified string. Returns a match array or null. If the provided regex uses named capture, named capture properties are included on the match array's groups property. Optional pos and sticky arguments specify the search start position, and whether the match must start at the specified position only. The lastIndex property of the provided regex is not used, but is updated for compatibility. Also fixes browser bugs compared to the native RegExp.prototype.exec and can be used reliably cross-browser.

Parameters:
  • str {String}
    String to search.
  • regex {RegExp}
    Regex to search with.
  • [pos=0] {Number}
    Zero-based index at which to start the search.
  • [sticky=false] {Boolean|String}
    Whether the match must start at the specified position only. The string 'sticky' is accepted as an alternative to true.
Returns: {Array}
Match array with named capture properties on the groups object, or null. If the namespacing feature is off, named capture properties are directly on the match array.

Example

// Basic use, with named backreference
let match = XRegExp.exec('U+2620', XRegExp('U\\+(?<hex>[0-9A-F]{4})'));
match.groups.hex; // -> '2620'

// With pos and sticky, in a loop
let pos = 3, result = [], match;
while (match = XRegExp.exec('<1><2><3><4>5<6>', /<(\d)>/, pos, 'sticky')) {
  result.push(match[1]);
  pos = match.index + match[0].length;
}
// result -> ['2', '3', '4']

XRegExp.forEach(str, regex, callback)

Executes a provided function once per regex match. Searches always start at the beginning of the string and continue until the end, regardless of the state of the regex's global property and initial lastIndex.

Parameters:
  • str {String}
    String to search.
  • regex {RegExp}
    Regex to search with.
  • callback {Function}
    Function to execute for each match. Invoked with four arguments:
    1. The match array, with named backreference properties.
    2. The zero-based match index.
    3. The string being traversed.
    4. The regex object being used to traverse the string.
Returns: {undefined}
Does not return a value.

Example

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

XRegExp.globalize(regex)

Copies a regex object and adds flag g. The copy maintains extended data, is augmented with XRegExp.prototype properties, and has a fresh lastIndex property (set to zero). Native regexes are not recompiled using XRegExp syntax.

Parameters:
  • regex {RegExp}
    Regex to globalize.
Returns: {RegExp}
Copy of the provided regex with flag g added.

Example

const globalCopy = XRegExp.globalize(/regex/);
globalCopy.global; // -> true

function parse(str, regex) {
  regex = XRegExp.globalize(regex);
  let match;
  while (match = regex.exec(str)) {
    // ...
  }
}

XRegExp.install(options)

Installs optional features according to the specified options. Can be undone using XRegExp.uninstall.

Parameters:
  • options {Object|String}
    Options object or string.
Returns: {undefined}
Does not return a value.

Example

// With an options object
XRegExp.install({
  // Enables support for astral code points in Unicode addons (implicitly sets flag A)
  astral: true,

  // Adds named capture groups to the `groups` property of matches
  // On by default in XRegExp 5
  namespacing: true
});

// With an options string
XRegExp.install('astral namespacing');

XRegExp.isInstalled(feature)

Checks whether an individual optional feature is installed.

Parameters:
  • feature {String}
    Name of the feature to check. One of:
    • astral
    • namespacing
Returns: {Boolean}
Whether the feature is installed.

Example

XRegExp.isInstalled('astral');

XRegExp.isRegExp(value)

Returns true if an object is a regex; false if it isn't. This works correctly for regexes created in another frame, when instanceof and constructor checks would fail.

Parameters:
  • value {*}
    Object to check.
Returns: {Boolean}
Whether the object is a RegExp object.

Example

XRegExp.isRegExp('string'); // -> false
XRegExp.isRegExp(/regex/i); // -> true
XRegExp.isRegExp(RegExp('^', 'm')); // -> true
XRegExp.isRegExp(XRegExp('(?s).')); // -> true

XRegExp.match(str, regex, [scope])

Returns the first matched string, or in global mode, an array containing all matched strings. This is essentially a more convenient re-implementation of String.prototype.match that gives the result types you actually want (string instead of exec-style array in match-first mode, and an empty array instead of null when no matches are found in match-all mode). It also lets you override flag g and ignore lastIndex, and fixes browser bugs.

Parameters:
  • str {String}
    String to search.
  • regex {RegExp}
    Regex to search with.
  • [scope='one'] {String}
    Use 'one' to return the first match as a string. Use 'all' to return an array of all matched strings. If not explicitly specified and regex uses flag g, scope is all.
Returns: {String|Array}
In match-first mode: First match as a string, or null. In match-all mode: Array of all matched strings, or an empty array.

Example

// Match first
XRegExp.match('abc', /\w/); // -> 'a'
XRegExp.match('abc', /\w/g, 'one'); // -> 'a'
XRegExp.match('abc', /x/g, 'one'); // -> null

// Match all
XRegExp.match('abc', /\w/g); // -> ['a', 'b', 'c']
XRegExp.match('abc', /\w/, 'all'); // -> ['a', 'b', 'c']
XRegExp.match('abc', /x/, 'all'); // -> []

XRegExp.matchChain(str, chain)

Retrieves the matches from searching a string using a chain of regexes that successively search within previous matches. The provided chain array can contain regexes and or objects with regex and backref properties. When a backreference is specified, the named or numbered backreference is passed forward to the next regex or returned.

Parameters:
  • str {String}
    String to search.
  • chain {Array}
    Regexes that each search for matches within preceding results.
Returns: {Array}
Matches by the last regex in the chain, or an empty array.

Example

// Basic usage; matches numbers within <b> tags
XRegExp.matchChain('1 <b>2</b> 3 <b>4 a 56</b>', [
  XRegExp('(?is)<b>.*?</b>'),
  /\d+/
]);
// -> ['2', '4', '56']

// Passing forward and returning specific backreferences
const html = `<a href="https://xregexp.com/api/">XRegExp</a>
              <a href="https://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.matchRecursive(str, left, right, [flags], [options])

Requires the XRegExp.matchRecursive addon, which is bundled in xregexp-all.js.

Returns an array of match strings between outermost left and right delimiters, or an array of objects with detailed match parts and position data. By default, an error is thrown if delimiters are unbalanced within the subject string.

Parameters:
  • str {String}
    String to search.
  • left {String}
    Left delimiter as an XRegExp pattern.
  • right {String}
    Right delimiter as an XRegExp pattern.
  • [flags] {String}
    Any combination of XRegExp flags, used for the left and right delimiters.
  • [options] {Object}
    Options object with optional properties:
    • valueNames {Array} Providing valueNames changes the return value from an array of matched strings to an array of objects that provide the value and start/end positions for the matched strings as well as the matched delimiters and unmatched string segments. To use this extended information mode, provide an array of 4 strings that name the parts to be returned:
      1. String segments outside of (before, between, and after) matches.
      2. Matched outermost left delimiters.
      3. Matched text between the outermost left and right delimiters.
      4. Matched outermost right delimiters.
      Taken together, these parts include the entire subject string if used with flag g.
      Use null for any of these values to omit unneeded parts from the returned results.
    • escapeChar {String} Single char used to escape delimiters within the subject string.
    • unbalanced {String} Handling mode for unbalanced delimiters. Options are:
      • 'error' - throw (default)
      • 'skip' - unbalanced delimiters are treated as part of the text between delimiters, and searches continue at the end of the unbalanced delimiter.
      • 'skip-lazy' - unbalanced delimiters are treated as part of the text between delimiters, and searches continue one character after the start of the unbalanced delimiter.
Returns:
  • {Array}
    Array of matches, or an empty array.

Example

// Basic usage
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']

XRegExp.replace(str, search, replacement, [scope])

Returns a new string with one or all matches of a pattern replaced. The pattern can be a string or regex, and the replacement can be a string or a function to be called for each match. To perform a global search and replace, use the optional scope argument or include flag g if using a regex. Replacement strings can use $<n> or ${n} for named and numbered backreferences. Replacement functions can use named backreferences via the last argument. Also fixes browser bugs compared to the native String.prototype.replace and can be used reliably cross-browser.

For the full details of XRegExp's replacement text syntax, see Syntax: Replacement text.

Parameters:
  • str {String}
    String to search.
  • search {RegExp|String}
    Search pattern to be replaced.
  • replacement {String|Function}
    Replacement string or a function invoked to create it.
    Replacement strings can include special replacement syntax:
    • $$ - Inserts a literal $ character.
    • $&, $0 - Inserts the matched substring.
    • $` - Inserts the string that precedes the matched substring (left context).
    • $' - Inserts the string that follows the matched substring (right context).
    • $n, $nn - Where n/nn are digits referencing an existent capturing group, inserts backreference n/nn.
    • $<n>, ${n} - Where n is a name or any number of digits that reference an existing capturing group, inserts backreference n.
    Replacement functions are invoked with three or more arguments:
    • args[0] - The matched substring (corresponds to $& above). If the namespacing feature is off, named backreferences are accessible as properties of this argument.
    • args[1..n] - One argument for each backreference (corresponding to $1, $2, etc. above). If the regex has no capturing groups, no arguments appear in this position.
    • args[n+1] - The zero-based index of the match within the entire search string.
    • args[n+2] - The total string being searched.
    • args[n+3] - If the the search pattern is a regex with named capturing groups, the last argument is the groups object. Its keys are the backreference names and its values are the backreference values. If the namespacing feature is off, this argument is not present.
  • [scope] {String}
    Use 'one' to replace the first match only, or 'all'. Defaults to 'one'. Defaults to 'all' if using a regex with flag g.
Returns: {String}
New string with one or all matches replaced.

Example

// Regex search, using named backreferences in replacement string
const name = XRegExp('(?<first>\\w+) (?<last>\\w+)');
XRegExp.replace('John Smith', name, '$<last>, $<first>');
// -> 'Smith, John'

// Regex search, using named backreferences in replacement function
XRegExp.replace('John Smith', name, (...args) => {
  const {first, last} = args.at(-1);
  return `${last}, ${first}`;
});
// -> 'Smith, John'

// String search, with replace-all
XRegExp.replace('RegExp builds RegExps', 'RegExp', 'XRegExp', 'all');
// -> 'XRegExp builds XRegExps'

XRegExp.replaceEach(str, replacements)

Performs batch processing of string replacements. Used like XRegExp.replace, but accepts an array of replacement details. Later replacements operate on the output of earlier replacements. Replacement details are accepted as an array with a regex or string to search for, the replacement string or function, and an optional scope of 'one' or 'all'. Uses the XRegExp replacement text syntax, which supports named backreference properties via $<name> or ${name}.

Parameters:
  • str {String}
    String to search.
  • replacements {Array}
    Array of replacement detail arrays.
Returns: {String}
New string with all replacements.

Example

str = XRegExp.replaceEach(str, [
  [XRegExp('(?<name>a)'), 'z$<name>'],
  [/b/gi, 'y'],
  [/c/g, 'x', 'one'], // scope 'one' overrides /g
  [/d/, 'w', 'all'],  // scope 'all' overrides lack of /g
  ['e', 'v', 'all'],  // scope 'all' allows replace-all for strings
  [/f/g, (match) => match.toUpperCase()]
]);

XRegExp.split(str, separator, [limit])

Splits a string into an array of strings using a regex or string separator. Matches of the separator are not included in the result array. However, if separator is a regex that contains capturing groups, backreferences are spliced into the result each time separator is matched. Fixes browser bugs compared to the native String.prototype.split and can be used reliably cross-browser.

Parameters:
  • str {String}
    String to split.
  • separator {RegExp|String}
    Regex or string to use for separating the string.
  • [limit] {Number}
    Maximum number of items to include in the result array.
Returns: {Array}
Array of substrings.

Example

// Basic use
XRegExp.split('a b c', ' ');
// -> ['a', 'b', 'c']

// With limit
XRegExp.split('a b c', ' ', 2);
// -> ['a', 'b']

// Backreferences in result array
XRegExp.split('..word1..', /([a-z]+)(\d+)/i);
// -> ['..', 'word', '1', '..']

XRegExp.tag([flags])`pattern`

Requires the XRegExp.build addon, which is bundled in xregexp-all.js.

Provides tagged template literals that create regexes with XRegExp syntax and flags. The provided pattern is handled as a raw string, so backslashes don't need to be escaped.

Interpolation of strings and regexes shares the features of XRegExp.build. Interpolated patterns are treated as atomic units when quantified, interpolated strings have their special characters escaped, a leading ^ and trailing unescaped $ are stripped from interpolated regexes if both are present, and any backreferences within an interpolated regex are rewritten to work within the overall pattern.

Parameters:
  • [flags] {String}
    Any combination of XRegExp flags.
  • pattern {String}
    Regex pattern as a raw string, optionally with interpolation.
Returns: {RegExp}
Extended regular expression object.

Example

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.test(str, regex, [pos], [sticky])

Executes a regex search in a specified string. Returns true or false. Optional pos and sticky arguments specify the search start position, and whether the match must start at the specified position only. The lastIndex property of the provided regex is not used, but is updated for compatibility. Also fixes browser bugs compared to the native RegExp.prototype.test and can be used reliably cross-browser.

Parameters:
  • str {String}
    String to search.
  • regex {RegExp}
    Regex to search with.
  • [pos=0] {Number}
    Zero-based index at which to start the search.
  • [sticky=false] {Boolean|String}
    Whether the match must start at the specified position only. The string 'sticky' is accepted as an alternative to true.
Returns: {Boolean}
Whether the regex matched the provided value.

Example

// Basic use
XRegExp.test('abc', /c/); // -> true

// With pos and sticky
XRegExp.test('abc', /c/, 0, 'sticky'); // -> false
XRegExp.test('abc', /c/, 2, 'sticky'); // -> true

XRegExp.uninstall(options)

Uninstalls optional features according to the specified options. Used to undo the actions of XRegExp.install.

Parameters:
  • options {Object|String}
    Options object or string.
Returns: {undefined}
Does not return a value.

Example

// With an options object
XRegExp.uninstall({
  // Disables support for astral code points in Unicode addons (unless enabled per regex)
  astral: true,

  // Don't add named capture groups to the `groups` property of matches
  namespacing: true
});

// With an options string
XRegExp.uninstall('astral namespacing');

XRegExp.union(patterns, [flags])

Returns an XRegExp object that is the union of the given patterns. Patterns can be provided as regex objects or strings. Metacharacters are escaped in patterns provided as strings. Backreferences in provided regex objects are automatically renumbered to work correctly within the larger combined pattern. Native flags used by provided regexes are ignored in favor of the flags argument.

Parameters:
  • patterns {Array}
    Regexes and strings to combine.
  • [flags] {String}
    Any combination of XRegExp flags.
  • [options] {Object}
    Options object with optional properties:
    • conjunction {String} Type of conjunction to use: 'or' (default) or 'none'.
Returns: {RegExp}
Union of the provided regexes and strings.

Example

XRegExp.union(['a+b*c', /(dogs)\1/, /(cats)\1/], 'i');
// -> /a\+b\*c|(dogs)\1|(cats)\2/i

XRegExp.union([/man/, /bear/, /pig/], 'i', {conjunction: 'none'});
// -> /manbearpig/i

XRegExp.version

The XRegExp version number as a string containing three dot-separated parts. For example, '2.0.0-beta-3'.

<regexp>.xregexp.source

The original pattern provided to the XRegExp constructor. Note that this differs from the <regexp>.source property which holds the transpiled source in native RegExp syntax and therefore can't be used to reconstruct the regex (e.g. <regexp>.source holds no knowledge of capture names). This property is available only for regexes originally constructed by XRegExp. It is null for native regexes copied using the XRegExp constructor or XRegExp.globalize.

<regexp>.xregexp.flags

The original flags provided to the XRegExp constructor. Differs from the ES6 <regexp>.flags property in that it includes XRegExp's non-native flags and is accessible even in pre-ES6 browsers. This property is available only for regexes originally constructed by XRegExp. It is null for native regexes copied using the XRegExp constructor or XRegExp.globalize. When regexes originally constructed by XRegExp are copied using XRegExp.globalize, the value of this property is augmented with 'g' if not already present. Flags are listed in alphabetical order.