RegExp
Конструктор RegExp
створює об'єкт регулярного виразу для знаходження тексту по шаблону.
Для ознайомлення з регулярними виразами, можете проглянути розділ Regular Expressions в JavaScript Guide.
Синтаксис
Можливі позначення літералу та констуктору:
/pattern/flags new RegExp(pattern[, flags])
Параметри
pattern
- Шаблон регулярного виразу.
flags
-
Якщо об'явлені, можуть сторювати комбінації з цих значень:
g
- глобальне співпадіння
i
- ігнорування розкладки
m
- співпадіння по кільком строкам; символи початку та кінця (
^
й $) починають працювати по кільком строкам (тобто відбувається співпадіння с початком або кінцем кожної строки (строки відділяються символами\n
й\r
), а не тільки з початком та кінцем усієї строки, яку ввели) u
- юнікод
y
- "липкий" пошук; починає шукати співпадіння з індексу, на який вказує властивість
lastIndex
даногоRegExp
Опис
Існує 2 шляхи створити RegExp
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:
/ab+c/i;
new RegExp('ab+c', 'i');
new RegExp(/ab+c/, 'i');
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.
Конструктор об'єкту регулярного виразу, приміром, new RegExp('ab+c')
, 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.
Починаючи з ECMAScript 6, new RegExp(/ab+c/, 'i')
більше не видає TypeError
("can't supply flags when constructing one RegExp from another") якщо перший аргумент RegExp
та другий аргумент flags
наявний. Натомість створюється новий RegExp
з аргументів.
При використанні функції-конструктора необхідно дотримуватись правил текстових рядків (попередні спеціальні символи з \ якщо вони входять в рядок). Наприклад, наступні вирази еквівалентні:
var re = /\w+/;
var re = new RegExp('\\w+');
Special characters meaning in regular expressions
Character Classes | |
---|---|
Character | Meaning |
. |
(The dot, the decimal point) matches any single character except line terminators: Inside a character class, the dot loses its special meaning and matches a literal dot. Note that the For example, |
\d |
Matches a digit character in the basic Latin alphabet. Equivalent to For example, |
\D |
Matches any character that is not a digit in the basic Latin alphabet. Equivalent to For example, |
\w |
Matches any alphanumeric character from the basic Latin alphabet, including the underscore. Equivalent to For example, |
\W |
Matches any character that is not a word character from the basic Latin alphabet. Equivalent to For example, |
\s |
Matches a single white space character, including space, tab, form feed, line feed and other Unicode spaces. Equivalent to For example, |
\S |
Matches a single character other than white space. Equivalent to For example, |
\t |
Matches a horizontal tab. |
\r |
Matches a carriage return. |
\n |
Matches a linefeed. |
\v |
Matches a vertical tab. |
\f |
Matches a form-feed. |
[\b] |
Matches a backspace. (Not to be confused with \b ) |
\0 |
Matches a NUL character. Do not follow this with another digit. |
\cX |
Where For example, |
\xhh |
Matches the character with the code hh (two hexadecimal digits). |
\uhhhh |
Matches a UTF-16 code-unit with the value hhhh (four hexadecimal digits). |
\u{hhhh} or \u{hhhhh} |
(only when u flag is set) Matches the character with the Unicode value U+hhhh or U+hhhhh (hexadecimal digits). |
\ |
For characters that are usually treated literally, indicates that the next character is special and not to be interpreted literally. For example, or For characters that are usually treated specially, indicates that the next character is not special and should be interpreted literally. For example, "*" is a special character that means 0 or more occurrences of the preceding character should be matched; for example, |
Character Sets | |
Character | Meaning |
[xyz] |
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. For example, |
|
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. For example, |
Alternation | |
Character | Meaning |
x|y |
Matches either For example, |
Boundaries | |
Character | Meaning |
^ |
Matches beginning of input. If the multiline flag is set to true, also matches immediately after a line break character. For example, |
$ |
Matches end of input. If the multiline flag is set to true, also matches immediately before a line break character. For example, |
\b |
Matches a zero-width word boundary, such as between a letter and a space. (Not to be confused with For example, |
\B |
Matches a zero-width non-word boundary, such as between two letters or between two spaces. For example, |
Grouping and back references | |
Character | Meaning |
(x) |
Matches For example, 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 Capturing groups have a performance penalty. If you don't need the matched substring to be recalled, prefer non-capturing parentheses (see below). |
\n |
Where For example, |
(?:x) |
Matches x 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 [1], ..., [n] or from the predefined RegExp object's properties $1, ..., $9 . |
Quantifiers | |
Character | Meaning |
x* |
Matches the preceding item x 0 or more times. For example, |
x+ |
Matches the preceding item x 1 or more times. Equivalent to For example, |
x? |
Matches the preceding item x 0 or 1 time. For example, If used immediately after any of the quantifiers |
x{n} |
Where For example, |
x{n,} |
Where For example, |
x{n,m} |
Where For example, |
|
Matches the preceding item x like For example, Quantifiers without |
Assertions | |
Character | Meaning |
x(?=y) |
Matches For example, / |
x(?!y) |
Matches For example, |
Properties
RegExp.prototype
(en-US)- Allows the addition of properties to all objects.
RegExp.length
- The value of
RegExp.length
is 2. get RegExp[@@species]
(en-US)- The constructor function that is used to create derived objects.
RegExp.lastIndex
(en-US)- The index at which to start the next match.
Methods
The global RegExp
object has no methods of its own, however, it does inherit some methods through the prototype chain.
RegExp
prototype objects and instances
Properties
Methods
Examples
Using a regular expression to change data format
The following script uses the replace()
method of the String
instance to match a name in the format first last and output it in the format last, first. In the replacement text, the script uses $1
and $2
to indicate the results of the corresponding matching parentheses in the regular expression pattern.
var re = /(\w+)\s(\w+)/;
var str = 'John Smith';
var newstr = str.replace(re, '$2, $1');
console.log(newstr);
This displays "Smith, John".
Using regular expression to split lines with different line endings/ends of line/line breaks
The default line ending varies depending on the platform (Unix, Windows, etc.). The line splitting provided in this example works on all platforms.
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' ]
Note that the order of the patterns in the regular expression matters.
Using regular expression on multiple lines
var s = 'Please yes\nmake my day!';
s.match(/yes.*day/);
// Returns null
s.match(/yes[^]*day/);
// Returns 'yes\nmake my day'
Using a regular expression with the sticky flag
The sticky flag indicates that the regular expression performs sticky matching in the target string by attempting to match starting at RegExp.prototype.lastIndex
(en-US).
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)
Regular expression and Unicode characters
As mentioned above, \w
or \W
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 \uhhhh
, where "hhhh" is the character's Unicode value in hexadecimal. This example demonstrates how one can separate out Unicode characters from a word.
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
Here's an external resource for getting the complete Unicode block range for different scripts: Regexp-unicode-block.
Extracting sub-domain name from URL
var url = 'http://xxx.domain.com';
console.log(/[^.]+/.exec(url)[0].substr(7)); // logs 'xxx'
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 3rd Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.1. |
ECMAScript 5.1 (ECMA-262) The definition of 'RegExp' in that specification. |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'RegExp' in that specification. |
Standard | The RegExp constructor no longer throws when the first argument is a RegExp and the second argument is present. Introduces Unicode and sticky flags. |
ECMAScript (ECMA-262) The definition of 'RegExp' in that specification. |
Living Standard |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Sticky flag ("y") | 39 [1] | 3.0 (1.9) | No support | No support | No support |
Unicode flag ("u") | 50 | 46 (46) | ? | ? | ? |
RegExp(RegExp object, flags) no longer throws |
No support | 39 (39) | No support | No support | No support |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Sticky flag ("y") | No support | No support | 1.0 (1.9) | No support | No support | No support |
Unicode flag ("u") | ? | 46.0 (46) | ? | ? | ? | |
RegExp(RegExp object, flags) no longer throws |
No support | No support | 39.0 (39) | No support | No support | No support |
[1] Behind a flag.
Gecko-specific notes
Starting with Gecko 34 (Firefox 34 / Thunderbird 34 / SeaMonkey 2.31), in the case of a capturing group with quantifiers preventing its exercise, the matched text for a capturing group is now undefined
instead of an empty string:
// 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'
Note that due to web compatibility, RegExp.$N
will still return an empty string instead of undefined
(bug 1053944).