path: root/files/uk/web/javascript/reference/global_objects/regexp/index.html

---
title: RegExp
slug: Web/JavaScript/Reference/Global_Objects/RegExp
tags:
  - Constructor
  - JavaScript
  - NeedsTranslation
  - Reference
  - RegExp
  - Regular Expressions
  - TopicStub
translation_of: Web/JavaScript/Reference/Global_Objects/RegExp
---
<div>{{JSRef}}</div>

<p>Конструктор <strong><code>RegExp </code></strong>створює об'єкт регулярного виразу для знаходження тексту по шаблону.</p>

<p>Для ознайомлення з регулярними виразами, можете проглянути розділ <a href="/en-US/docs/Web/JavaScript/Guide/Regular_Expressions">Regular Expressions</a> в <a href="/en-US/docs/Web/JavaScript/Guide/Regular_Expressions">JavaScript Guide</a>.</p>

<h2 id="Синтаксис">Синтаксис</h2>

<p>Можливі позначення літералу та констуктору:</p>

<pre class="syntaxbox notranslate">/<var>pattern</var>/<var>flags</var>
new RegExp(<var>pattern</var>[, <var>flags</var>])
</pre>

<h3 id="Параметри">Параметри</h3>

<dl>
 <dt><code>pattern</code></dt>
 <dd>Шаблон регулярного виразу.</dd>
 <dt><code>flags</code></dt>
 <dd>
 <p>Якщо об'явлені, можуть сторювати комбінації з цих значень:</p>

 <dl>
  <dt><code>g</code></dt>
  <dd>глобальне співпадіння</dd>
  <dt><code>i</code></dt>
  <dd>ігнорування розкладки</dd>
  <dt><code>m</code></dt>
  <dd>співпадіння по кільком строкам; символи початку та кінця (<code>^</code> й <font face="consolas, Liberation Mono, courier, monospace"><span style="background-color: rgba(220, 220, 220, 0.5);">$</span></font>) починають працювати по кільком строкам (тобто відбувається співпадіння с початком або кінцем <em>кожної </em>строки (строки відділяються символами <code>\n</code> й <code>\r</code>), а не тільки з початком та кінцем усієї строки, яку ввели)</dd>
  <dt><code>u</code></dt>
  <dd>юнікод</dd>
  <dt><code>y</code></dt>
  <dd>"липкий" пошук; починає шукати співпадіння з індексу, на який вказує властивість <code>lastIndex</code> даного <code>RegExp</code></dd>
 </dl>
 </dd>
</dl>

<h2 id="Опис">Опис</h2>

<p>Існує 2 шляхи створити <code>RegExp</code> об'єкт: за допомогою літерального виразу або конструктора. Аби розрізняти текстовий рядок, параметри літерального виразу не містять лапок, але якщо створювати за допомогою конструктора, то лапки можно використовувати. У наступному прикладі створюються однакові регулярні вирази:</p>

<pre class="brush: js notranslate">/ab+c/i;
new RegExp('ab+c', 'i');
new RegExp(/ab+c/, 'i');
</pre>

<p>Літеральна нотація виконує компіляцію виразу коли даний вираз обчислений. Викоритсовуйте літерали якщо регулярний вираз відомий до початку роботи програми. Наприклад, якщо використовувати літерал у циклі, регулярний вираз не буде наново компілюватись на кожній ітерації.</p>

<p>Конструктор об'єкту регулярного виразу, приміром, <code>new RegExp('ab+c')</code>, забезпечує компіляцію регулярного виразу під час виконання програми. Використовуйте функцію конструктора якщо шаблон регулярного виразу буде змінюватися або шаблон не відомий та надходить з іншого джерела, наприклад, від користувача.</p>

<p>Починаючи з ECMAScript 6, <code>new RegExp(/ab+c/, 'i')</code> більше не видає {{jsxref("TypeError")}} ("can't supply flags when constructing one RegExp from another") якщо перший аргумент <code>RegExp</code> та другий аргумент <code>flags</code> наявний. Натомість створюється новий <code>RegExp</code> з аргументів.</p>

<p>При використанні функції-конструктора необхідно дотримуватись правил текстових рядків (попередні спеціальні символи з \ якщо вони входять в рядок). Наприклад, наступні вирази еквівалентні:</p>

<pre class="brush: js notranslate">var re = /\w+/;
var re = new RegExp('\\w+');
</pre>

<h2 id="Special_characters_meaning_in_regular_expressions">Special characters meaning in regular expressions</h2>

<ul>
 <li><a href="#character-classes">Character Classes</a></li>
 <li><a href="#character-sets">Character Sets</a></li>
 <li><a href="#boundaries">Boundaries</a></li>
 <li><a href="#grouping-back-references">Grouping and back references</a></li>
 <li><a href="#quantifiers">Quantifiers</a></li>
</ul>

<table class="fullwidth-table">
 <tbody>
  <tr id="character-classes">
   <th colspan="2">Character Classes</th>
  </tr>
  <tr>
   <th>Character</th>
   <th>Meaning</th>
  </tr>
  <tr>
   <td><code>.</code></td>
   <td>
    <p>(The dot, the decimal point) matches any single character <em>except</em> line terminators: <code>\n</code>, <code>\r</code>, <code>\u2028</code> or <code>\u2029</code>.</p>

    <p>Inside a character class, the dot loses its special meaning and matches a literal dot.</p>

    <p>Note that the <code>m</code> multiline flag doesn't change the dot behavior. So to match a pattern across multiple lines, the character set <code>[^]</code> can be used (if you don't mean an old version of IE, of course), it will match any character including newlines.</p>

    <p>For example, <code>/.y/</code> matches "my" and "ay", but not "yes", in "yes make my day".</p>
   </td>
  </tr>
  <tr>
   <td><code>\d</code></td>
   <td>
    <p>Matches a digit character in the basic Latin alphabet. Equivalent to <code>[0-9]</code>.</p>

    <p>For example, <code>/\d/</code> or <code>/[0-9]/</code> matches "2" in "B2 is the suite number".</p>
   </td>
  </tr>
  <tr>
   <td><code>\D</code></td>
   <td>
    <p>Matches any character that is not a digit in the basic Latin alphabet. Equivalent to <code>[^0-9]</code>.</p>

    <p>For example, <code>/\D/</code> or <code>/[^0-9]/</code> matches "B" in "B2 is the suite number".</p>
   </td>
  </tr>
  <tr>
   <td><code>\w</code></td>
   <td>
    <p>Matches any alphanumeric character from the basic Latin alphabet, including the underscore. Equivalent to <code>[A-Za-z0-9_]</code>.</p>

    <p>For example, <code>/\w/</code> matches "a" in "apple", "5" in "$5.28", and "3" in "3D".</p>
   </td>
  </tr>
  <tr>
   <td><code>\W</code></td>
   <td>
    <p>Matches any character that is not a word character from the basic Latin alphabet. Equivalent to <code>[^A-Za-z0-9_]</code>.</p>

    <p>For example, <code>/\W/</code> or <code>/[^A-Za-z0-9_]/</code> matches "%" in "50%".</p>
   </td>
  </tr>
  <tr>
   <td><code>\s</code></td>
   <td>
    <p>Matches a single white space character, including space, tab, form feed, line feed and other Unicode spaces. Equivalent to <code>[ \f\n\r\t\v​\u00a0\u1680​\u180e\u2000​-\u200a​\u2028\u2029\u202f\u205f​\u3000\ufeff]</code>.</p>

    <p>For example, <code>/\s\w*/</code> matches " bar" in "foo bar".</p>
   </td>
  </tr>
  <tr>
   <td><code>\S</code></td>
   <td>
    <p>Matches a single character other than white space. Equivalent to <code>[^ \f\n\r\t\v​\u00a0\u1680​\u180e\u2000​-\u200a​\u2028\u2029\u202f\u205f​\u3000\ufeff]</code>.</p>

    <p>For example, <code>/\S\w*/</code> matches "foo" in "foo bar".</p>
   </td>
  </tr>
  <tr>
   <td><code>\t</code></td>
   <td>Matches a horizontal tab.</td>
  </tr>
  <tr>
   <td><code>\r</code></td>
   <td>Matches a carriage return.</td>
  </tr>
  <tr>
   <td><code>\n</code></td>
   <td>Matches a linefeed.</td>
  </tr>
  <tr>
   <td><code>\v</code></td>
   <td>Matches a vertical tab.</td>
  </tr>
  <tr>
   <td><code>\f</code></td>
   <td>Matches a form-feed.</td>
  </tr>
  <tr>
   <td><code>[\b]</code></td>
   <td>Matches a backspace. (Not to be confused with <code>\b</code>)</td>
  </tr>
  <tr>
   <td><code>\0</code></td>
   <td>Matches a NUL character. Do not follow this with another digit.</td>
  </tr>
  <tr>
   <td><code>\c<em>X</em></code></td>
   <td>
    <p>Where <code><em>X</em></code> is a letter from A - Z. Matches a control character in a string.</p>

    <p>For example, <code>/\cM/</code> matches control-M in a string.</p>
   </td>
  </tr>
  <tr>
   <td><code>\x<em>hh</em></code></td>
   <td>Matches the character with the code <code><em>hh</em></code> (two hexadecimal digits).</td>
  </tr>
  <tr>
   <td><code>\u<em>hhhh</em></code></td>
   <td>Matches a UTF-16 code-unit with the value <code><em>hhhh</em></code> (four hexadecimal digits).</td>
  </tr>
  <tr>
   <td><code>\u<em>{hhhh} </em>or <em>\u{hhhhh}</em></code></td>
   <td>(only when u flag is set) Matches the character with the Unicode value U+<code><em>hhhh</em> or </code>U+<code><em>hhhhh</em></code> (hexadecimal digits).</td>
  </tr>
  <tr>
   <td><code>\</code></td>
   <td>
    <p>For characters that are usually treated literally, indicates that the next character is special and not to be interpreted literally.</p>

    <p>For example, <code>/b/</code> matches the character "b". By placing a backslash in front of "b", that is by using <code>/\b/</code>, the character becomes special to mean match a word boundary.</p>

    <p><em>or</em></p>

    <p>For characters that are usually treated specially, indicates that the next character is not special and should be interpreted literally.</p>

    <p>For example, "*" is a special character that means 0 or more occurrences of the preceding character should be matched; for example, <code>/a*/</code> means match 0 or more "a"s. To match <code>*</code> literally, precede it with a backslash; for example, <code>/a\*/</code> matches "a*".</p>
   </td>
  </tr>
 </tbody>
 <tbody>
  <tr id="character-sets">
   <th colspan="2">Character Sets</th>
  </tr>
  <tr>
   <th>Character</th>
   <th>Meaning</th>
  </tr>
  <tr>
   <td><code>[xyz]<br>
    [a-c]</code></td>
   <td>
    <p>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.</p>

    <p>For example, <code>[abcd]</code> is the same as <code>[a-d]</code>. They match the "b" in "brisket" and the "c" in "chop".</p>
   </td>
  </tr>
  <tr>
   <td>
    <p><code>[^xyz]<br>
     [^a-c]</code></p>
   </td>
   <td>
    <p>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.</p>

    <p>For example, <code>[^abc]</code> is the same as <code>[^a-c]</code>. They initially match "o" in "bacon" and "h" in "chop".</p>
   </td>
  </tr>
 </tbody>
 <tbody>
  <tr id="alternation">
   <th colspan="2">Alternation</th>
  </tr>
  <tr>
   <th>Character</th>
   <th>Meaning</th>
  </tr>
  <tr>
   <td><code><em>x</em>|<em>y</em></code></td>
   <td>
    <p>Matches either <code><em>x</em></code> or <code><em>y</em></code>.</p>

    <p>For example, <code>/green|red/</code> matches "green" in "green apple" and "red" in "red apple".</p>
   </td>
  </tr>
 </tbody>
 <tbody>
  <tr id="boundaries">
   <th colspan="2">Boundaries</th>
  </tr>
  <tr>
   <th>Character</th>
   <th>Meaning</th>
  </tr>
  <tr>
   <td><code>^</code></td>
   <td>
    <p>Matches beginning of input. If the multiline flag is set to true, also matches immediately after a line break character.</p>

    <p>For example, <code>/^A/</code> does not match the "A" in "an A", but does match the first "A" in "An A".</p>
   </td>
  </tr>
  <tr>
   <td><code>$</code></td>
   <td>
    <p>Matches end of input. If the multiline flag is set to true, also matches immediately before a line break character.</p>

    <p>For example, <code>/t$/</code> does not match the "t" in "eater", but does match it in "eat".</p>
   </td>
  </tr>
  <tr>
   <td><code>\b</code></td>
   <td>
    <p>Matches a zero-width word boundary, such as between a letter and a space. (Not to be confused with <code>[\b]</code>)</p>

    <p>For example, <code>/\bno/</code> matches the "no" in "at noon"; <code>/ly\b/</code> matches the "ly" in "possibly yesterday".</p>
   </td>
  </tr>
  <tr>
   <td><code>\B</code></td>
   <td>
    <p>Matches a zero-width non-word boundary, such as between two letters or between two spaces.</p>

    <p>For example, <code>/\Bon/</code> matches "on" in "at noon", and <code>/ye\B/</code> matches "ye" in "possibly yesterday".</p>
   </td>
  </tr>
 </tbody>
 <tbody>
  <tr id="grouping-back-references">
   <th colspan="2">Grouping and back references</th>
  </tr>
  <tr>
   <th>Character</th>
   <th>Meaning</th>
  </tr>
  <tr>
   <td><code>(<em>x</em>)</code></td>
   <td>
    <p>Matches <code><em>x</em></code> and remembers the match. These are called capturing groups.</p>

    <p>For example, <code>/(foo)/</code> matches and remembers "foo" in "foo bar". </p>

    <p>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 <code>[1], ..., [n]</code> or from the predefined <code>RegExp</code> object's properties <code>$1, ..., $9</code>.</p>

    <p>Capturing groups have a performance penalty. If you don't need the matched substring to be recalled, prefer non-capturing parentheses (see below).</p>
   </td>
  </tr>
  <tr>
   <td><code>\<em>n</em></code></td>
   <td>
    <p>Where <code><em>n</em></code> is a positive integer. A back reference to the last substring matching the n parenthetical in the regular expression (counting left parentheses).</p>

    <p>For example, <code>/apple(,)\sorange\1/</code> matches "apple, orange," in "apple, orange, cherry, peach". A more complete example follows this table.</p>
   </td>
  </tr>
  <tr>
   <td><code>(?:<em>x</em>)</code></td>
   <td>Matches <code><em>x</em></code> but does not remember the match. These are called non-capturing groups. The matched substring can not be recalled from the resulting array's elements <code>[1], ..., [n]</code> or from the predefined <code>RegExp</code> object's properties <code>$1, ..., $9</code>.</td>
  </tr>
 </tbody>
 <tbody>
  <tr id="quantifiers">
   <th colspan="2">Quantifiers</th>
  </tr>
  <tr>
   <th>Character</th>
   <th>Meaning</th>
  </tr>
  <tr>
   <td><code><em>x</em>*</code></td>
   <td>
    <p>Matches the preceding item <em>x</em> 0 or more times.</p>

    <p>For example, <code>/bo*/</code> matches "boooo" in "A ghost booooed" and "b" in "A bird warbled", but nothing in "A goat grunted".</p>
   </td>
  </tr>
  <tr>
   <td><code><em>x</em>+</code></td>
   <td>
    <p>Matches the preceding item <em>x</em> 1 or more times. Equivalent to <code>{1,}</code>.</p>

    <p>For example, <code>/a+/</code> matches the "a" in "candy" and all the "a"'s in "caaaaaaandy".</p>
   </td>
  </tr>
  <tr>
   <td><code><em>x</em>?</code></td>
   <td>
    <p>Matches the preceding item <em>x</em> 0 or 1 time.</p>

    <p>For example, <code>/e?le?/</code> matches the "el" in "angel" and the "le" in "angle."</p>

    <p>If used immediately after any of the quantifiers <code>*</code>, <code>+</code>, <code>?</code>, or <code>{}</code>, makes the quantifier non-greedy (matching the minimum number of times), as opposed to the default, which is greedy (matching the maximum number of times).</p>
   </td>
  </tr>
  <tr>
   <td><code><em>x</em>{<em>n</em>}</code></td>
   <td>
    <p>Where <code><em>n</em></code> is a positive integer. Matches exactly <code><em>n</em></code> occurrences of the preceding item <em>x</em>.</p>

    <p>For example, <code>/a{2}/</code> doesn't match the "a" in "candy", but it matches all of the "a"'s in "caandy", and the first two "a"'s in "caaandy".</p>
   </td>
  </tr>
  <tr>
   <td><code><em>x</em>{<em>n</em>,}</code></td>
   <td>
    <p>Where <code><em>n</em></code> is a positive integer. Matches at least <code><em>n</em></code> occurrences of the preceding item <em>x</em>.</p>

    <p>For example, <code>/a{2,}/</code> doesn't match the "a" in "candy", but matches all of the a's in "caandy" and in "caaaaaaandy".</p>
   </td>
  </tr>
  <tr>
   <td><code><em>x</em>{<em>n</em>,<em>m</em>}</code></td>
   <td>
    <p>Where <code><em>n</em></code> and <code><em>m</em></code> are positive integers. Matches at least <code><em>n</em></code> and at most <code><em>m</em></code> occurrences of the preceding item <em>x</em>.</p>

    <p>For example, <code>/a{1,3}/</code> matches nothing in "cndy", the "a" in "candy", the two "a"'s in "caandy", and the first three "a"'s in "caaaaaaandy". Notice that when matching "caaaaaaandy", the match is "aaa", even though the original string had more "a"'s in it.</p>
   </td>
  </tr>
  <tr>
   <td>
    <p><code><em>x</em>*?</code><br>
     <code><em>x</em>+?</code><br>
     <code><em>x</em>??</code><br>
     <code><em>x</em>{n}?</code><br>
     <code><em>x</em>{n,}?</code><br>
     <code><em>x</em>{n,m}?</code></p>
   </td>
   <td>
    <p>Matches the preceding item <em>x</em> like <code>*</code>, <code>+</code>, <code>?</code>, and <code>{...}</code> from above, however the match is the smallest possible match.</p>

    <p>For example, <code>/&lt;.*?&gt;/</code> matches "&lt;foo&gt;" in "&lt;foo&gt; &lt;bar&gt;", whereas <code>/&lt;.*&gt;/</code> matches "&lt;foo&gt; &lt;bar&gt;".</p>

    <p>Quantifiers without <code>?</code> are said to be greedy. Those with <code>?</code> are called "non-greedy".</p>
   </td>
  </tr>
 </tbody>
 <tbody>
  <tr id="assertions">
   <th colspan="2">Assertions</th>
  </tr>
  <tr>
   <th>Character</th>
   <th>Meaning</th>
  </tr>
  <tr>
   <td><code><em>x</em>(?=<em>y</em>)</code></td>
   <td>
    <p>Matches <code><em>x</em></code> only if <code><em>x</em></code> is followed by <code><em>y</em></code>.</p>

    <p>For example, /<code>Jack(?=Sprat)/</code> matches "Jack" only if it is followed by "Sprat".<br>
     <code>/Jack(?=Sprat|Frost)/</code> matches "Jack" only if it is followed by "Sprat" or "Frost". However, neither "Sprat" nor "Frost" is part of the match results.</p>
   </td>
  </tr>
  <tr>
   <td><code><em>x</em>(?!<em>y</em>)</code></td>
   <td>
    <p>Matches <code><em>x</em></code> only if <code><em>x</em></code> is not followed by <code><em>y</em></code>.</p>

    <p>For example, <code>/\d+(?!\.)/</code> matches a number only if it is not followed by a decimal point.<br>
     <code>/\d+(?!\.)/.exec('3.141')</code> matches "141" but not "3.141".</p>
   </td>
  </tr>
 </tbody>
</table>

<h2 id="Properties">Properties</h2>

<dl>
 <dt>{{jsxref("RegExp.prototype")}}</dt>
 <dd>Allows the addition of properties to all objects.</dd>
 <dt><code>RegExp.length</code></dt>
 <dd>The value of <code>RegExp.length</code> is 2.</dd>
 <dt>{{jsxref("RegExp.@@species", "get RegExp[@@species]")}}</dt>
 <dd>The constructor function that is used to create derived objects.</dd>
 <dt>{{jsxref("RegExp.lastIndex")}}</dt>
 <dd>The index at which to start the next match.</dd>
</dl>

<h2 id="Methods">Methods</h2>

<p>The global <code>RegExp</code> object has no methods of its own, however, it does inherit some methods through the prototype chain.</p>

<h2 id="RegExp_prototype_objects_and_instances"><code>RegExp</code> prototype objects and instances</h2>

<h3 id="Properties_2">Properties</h3>

<div>{{page('/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/prototype', 'Properties')}}</div>

<h3 id="Methods_2">Methods</h3>

<div>{{page('/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/prototype', 'Methods')}}</div>

<h2 id="Examples">Examples</h2>

<h3 id="Using_a_regular_expression_to_change_data_format">Using a regular expression to change data format</h3>

<p>The following script uses the {{jsxref("String.prototype.replace()", "replace()")}} method of the {{jsxref("Global_Objects/String", "String")}} instance to match a name in the format <em>first last</em> and output it in the format <em>last, first</em>. In the replacement text, the script uses <code>$1</code> and <code>$2</code> to indicate the results of the corresponding matching parentheses in the regular expression pattern.</p>

<pre class="brush: js notranslate">var re = /(\w+)\s(\w+)/;
var str = 'John Smith';
var newstr = str.replace(re, '$2, $1');
console.log(newstr);
</pre>

<p>This displays "Smith, John".</p>

<h3 id="Using_regular_expression_to_split_lines_with_different_line_endingsends_of_lineline_breaks">Using regular expression to split lines with different <strong>line endings/ends of line/line breaks</strong></h3>

<p>The default line ending varies depending on the platform (Unix, Windows, etc.). The line splitting provided in this example works on all platforms.</p>

<pre class="brush: js notranslate">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' ]
</pre>

<p>Note that the order of the patterns in the regular expression matters.</p>

<h3 id="Using_regular_expression_on_multiple_lines">Using regular expression on multiple lines</h3>

<pre class="brush: js notranslate">var s = 'Please yes\nmake my day!';
s.match(/yes.*day/);
// Returns null
s.match(/yes[^]*day/);
// Returns 'yes\nmake my day'
</pre>

<h3 id="Using_a_regular_expression_with_the_sticky_flag">Using a regular expression with the sticky flag</h3>

<p>The <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/sticky">sticky flag</a> indicates that the regular expression performs sticky matching in the target string by attempting to match starting at {{jsxref("RegExp.prototype.lastIndex")}}.</p>

<pre class="brush: js notranslate">var str = '#foo#';
var regex = /foo/y;

regex.lastIndex; // 0
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)</pre>

<h3 id="Regular_expression_and_Unicode_characters">Regular expression and Unicode characters</h3>

<p>As mentioned above, <code>\w</code> or <code>\W</code> 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 <code>\uhhhh</code>, where "hhhh" is the character's Unicode value in hexadecimal. This example demonstrates how one can separate out Unicode characters from a word.</p>

<pre class="brush: js notranslate">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
</pre>

<p>Here's an external resource for getting the complete Unicode block range for different scripts: <a href="http://kourge.net/projects/regexp-unicode-block">Regexp-unicode-block</a>.</p>

<h3 id="Extracting_sub-domain_name_from_URL">Extracting sub-domain name from URL</h3>

<pre class="brush: js notranslate">var url = 'http://xxx.domain.com';
console.log(/[^.]+/.exec(url)[0].substr(7)); // logs 'xxx'
</pre>

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('ES3')}}</td>
   <td>{{Spec2('ES3')}}</td>
   <td>Initial definition. Implemented in JavaScript 1.1.</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-15.10', 'RegExp')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-regexp-regular-expression-objects', 'RegExp')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>The <code>RegExp</code> constructor no longer throws when the first argument is a <code>RegExp</code> and the second argument is present. Introduces Unicode and sticky flags.</td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-regexp-regular-expression-objects', 'RegExp')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td></td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>

<div>{{CompatibilityTable}}</div>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
  <tr>
   <td>Sticky flag ("y")</td>
   <td>{{CompatChrome("39")}} [1]</td>
   <td>{{CompatGeckoDesktop("1.9")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
  </tr>
  <tr>
   <td>Unicode flag ("u")</td>
   <td>{{CompatChrome("50")}}</td>
   <td>{{CompatGeckoDesktop("46")}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
  </tr>
  <tr>
   <td><code>RegExp(RegExp object, flags)</code> no longer throws</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatGeckoDesktop("39")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Chrome for Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
  <tr>
   <td>Sticky flag ("y")</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatGeckoMobile("1.9")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
  </tr>
  <tr>
   <td>Unicode flag ("u")</td>
   <td>{{CompatUnknown }}</td>
   <td>{{CompatGeckoMobile("46")}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatUnknown}}</td>
  </tr>
  <tr>
   <td><code>RegExp(RegExp object, flags)</code> no longer throws</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatGeckoMobile("39")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
  </tr>
 </tbody>
</table>
</div>

<p>[1] Behind a flag.</p>

<h2 id="Gecko-specific_notes">Gecko-specific notes</h2>

<p>Starting with Gecko 34 {{geckoRelease(34)}}, in the case of a capturing group with quantifiers preventing its exercise, the matched text for a capturing group is now <code>undefined</code> instead of an empty string:</p>

<pre class="brush: js notranslate">// 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'
</pre>

<p>Note that due to web compatibility, <code>RegExp.$N</code> will still return an empty string instead of <code>undefined</code> ({{bug(1053944)}}).</p>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Guide/Regular_Expressions">Regular Expressions</a> chapter in the <a href="/en-US/docs/Web/JavaScript/Guide">JavaScript Guide</a></li>
 <li>{{jsxref("String.prototype.match()")}}</li>
 <li>{{jsxref("String.prototype.replace()")}}</li>
</ul>