RegExp

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RegExp 物件被用來比對符合自訂規則的文字。

關於正規表達式(regular expressions)的介紹,可以閱讀 JavaScript 指南中的 正規表達式章節

說明

建立 RegExp 物件有兩種方式:文字表示法 (literal notation) 和 建構子 (constructor)。

  • 文字表示法 的參數,頭尾以斜線標註,且不使用引號標註。
  • 建構子函式 的參數,頭尾不以斜線標註,但使用引號標註。

以下的表達式會建立出相同的正規表達式:

/ab+c/i
new RegExp(/ab+c/, 'i') // literal notation
new RegExp('ab+c', 'i') // constructor

The literal notation provides a compilation of the regular expression when the expression is evaluated. Use literal notation when the regular expression will remain constant. For example, if you use literal notation to construct a regular expression used in a loop, the regular expression won't be recompiled on each iteration.

The constructor of the regular expression object—for example, new RegExp('ab+c')—provides runtime compilation of the regular expression. Use the constructor function when you know the regular expression pattern will be changing, or you don't know the pattern and are getting it from another source, such as user input.

Starting with ECMAScript 6, new RegExp(/ab+c/, 'i') no longer throws a TypeError ("can't supply flags when constructing one RegExp from another") when the first argument is a RegExp and the second flags argument is present. A new RegExp from the arguments is created instead.

When using the constructor function, the normal string escape rules (preceding special characters with \ when included in a string) are necessary.

For example, the following are equivalent:

let re = /\w+/
let re = new RegExp('\\w+')

Constructor

RegExp()
Creates a regular expression object.

Properties

RegExp.prototype
Allows the addition of properties to all objects.
RegExp.length
The value of RegExp.length is 2.
get RegExp[@@species]
The constructor function that is used to create derived objects.
RegExp.lastIndex
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

See also deprecated RegExp properties.

Note that several of the RegExp properties have both long and short (Perl-like) names. Both names always refer to the same value. Perl is the programming language from which JavaScript modeled its regular expressions.

RegExp.prototype.constructor
Specifies the function that creates an object's prototype.
RegExp.prototype.flags
A string that contains the flags of the RegExp object.
RegExp.prototype.dotAll
Whether . matches newlines or not.
RegExp.prototype.global
Whether to test the regular expression against all possible matches in a string, or only against the first.
RegExp.prototype.ignoreCase
Whether to ignore case while attempting a match in a string.
RegExp.prototype.multiline
Whether or not to search in strings across multiple lines.
RegExp.prototype.source
The text of the pattern.
RegExp.prototype.sticky
Whether or not the search is sticky.
RegExp.prototype.unicode
Whether or not Unicode features are enabled.

Methods

RegExp.prototype.compile()
(Re-)compiles a regular expression during execution of a script.
RegExp.prototype.exec()
Executes a search for a match in its string parameter.
RegExp.prototype.test()
Tests for a match in its string parameter.
RegExp.prototype[@@match]()
Performs match to given string and returns match result.
RegExp.prototype[@@matchAll]()
Returns all matches of the regular expression against a string.
RegExp.prototype[@@replace]()
Replaces matches in given string with new substring.
RegExp.prototype[@@search]()
Searches the match in given string and returns the index the pattern found in the string.
RegExp.prototype[@@split]()
Splits given string into an array by separating the string into substring.
RegExp.prototype.toSource()
Returns an object literal representing the specified object; you can use this value to create a new object. Overrides the Object.prototype.toSource() method.
RegExp.prototype.toString()
Returns a string representing the specified object. Overrides the Object.prototype.toString() method.

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.

let re = /(\w+)\s(\w+)/
let str = 'John Smith'
let 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.

let text = 'Some text\nAnd some more\r\nAnd yet\rThis is the end'
let 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

let 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.

let str = '#foo#'
let regex = /foo/y

regex.lastIndex = 1
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)

The difference between the sticky flag and the global flag

With the sticky flag y, the next match has to happen at the lastIndex position, while with the global flag g, the match can happen at the lastIndex position or later:

re = /\d/y;
while (r = re.exec("123 456")) console.log(r, "AND re.lastIndex", re.lastIndex);

// [ '1', index: 0, input: '123 456', groups: undefined ] AND re.lastIndex 1
// [ '2', index: 1, input: '123 456', groups: undefined ] AND re.lastIndex 2
// [ '3', index: 2, input: '123 456', groups: undefined ] AND re.lastIndex 3
//   ... and no more match.

With the global flag g, all 6 digits would be matched, not just 3.

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.

let text = 'Образец text на русском языке'
let regex = /[\u0400-\u04FF]+/g

let match = regex.exec(text)
console.log(match[0])        // logs 'Образец'
console.log(regex.lastIndex) // logs '7'

let match2 = regex.exec(text)
console.log(match2[0])       // logs 'на' [did not log 'text']
console.log(regex.lastIndex) // logs '15'

// and so on

The Unicode property escapes feature introduces a solution, by allowing for a statement as simple as \p{scx=Cyrl}. One can also use an external resource for getting the complete Unicode block range for different scripts, such as Regexp-Unicode-block.

Extracting sub-domain name from URL

let url = 'http://xxx.domain.com'
console.log(/[^.]+/.exec(url)[0].substr(7)) // logs 'xxx'

Specifications

Specification
ECMAScript (ECMA-262)
The definition of 'RegExp' in that specification.

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
RegExpChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp() constructorChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
compile
Deprecated
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 6Safari Full support 3.1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 2Samsung Internet Android Full support 1.0nodejs Full support Yes
dotAllChrome Full support 62Edge Full support 79Firefox Full support 78IE No support NoOpera Full support 49Safari Full support 12WebView Android Full support 62Chrome Android Full support 62Firefox Android No support NoOpera Android Full support 46Safari iOS Full support 12Samsung Internet Android Full support 8.0nodejs Full support 8.10.0
Full support 8.10.0
Full support 8.3.0
Disabled
Disabled From version 8.3.0: this feature is behind the --harmony runtime flag.
execChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
flagsChrome Full support 49Edge Full support 79Firefox Full support 37IE No support NoOpera Full support 39Safari Full support 9WebView Android Full support 49Chrome Android Full support 49Firefox Android Full support 37Opera Android Full support 41Safari iOS Full support 9Samsung Internet Android Full support 5.0nodejs Full support 6.0.0
globalChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
ignoreCaseChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.input ($_)
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 15Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 14Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
lastIndexChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.lastMatch ($&)
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 10.5Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 11Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.lastParen ($+)
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 10.5Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 11Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.leftContext ($`)
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 8Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
lookbehind assertions ((?<= ) and (?<! ))Chrome Full support 62Edge Full support 79Firefox Full support 78IE No support NoOpera Full support 49Safari No support NoWebView Android Full support 62Chrome Android Full support 62Firefox Android No support No
Notes
No support No
Notes
Notes See bug 1225665.
Opera Android Full support 46Safari iOS No support NoSamsung Internet Android Full support 8.0nodejs Full support 8.10.0
multilineChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
RegExp.$1-$9Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
Named capture groupsChrome Full support 64Edge Full support 79Firefox Full support 78IE No support NoOpera Full support 51Safari Full support 11.1WebView Android Full support 64Chrome Android Full support 64Firefox Android No support NoOpera Android Full support 47Safari iOS Full support 11.3Samsung Internet Android Full support 9.0nodejs Full support 10.0.0
Full support 10.0.0
Full support 8.3.0
Disabled
Disabled From version 8.3.0: this feature is behind the --harmony runtime flag.
Unicode property escapes (\p{...})Chrome Full support 64Edge Full support 79Firefox Full support 78IE No support NoOpera Full support 51Safari Full support 11.1WebView Android Full support 64Chrome Android Full support 64Firefox Android No support NoOpera Android Full support 47Safari iOS Full support 11.3Samsung Internet Android Full support 9.0nodejs Full support 10.0.0
Full support 10.0.0
Full support 8.3.0
Disabled
Disabled From version 8.3.0: this feature is behind the --harmony runtime flag.
RegExp.rightContext ($')
Non-standard
Chrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 5.5Opera Full support 8Safari Full support 3WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
sourceChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
stickyChrome Full support 49Edge Full support 13Firefox Full support 3IE No support NoOpera Full support 36Safari Full support 10WebView Android Full support 49Chrome Android Full support 49Firefox Android Full support 4Opera Android Full support 36Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support Yes
testChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
toSource
Non-standard
Chrome No support NoEdge No support NoFirefox No support 1 — 74
Notes
No support 1 — 74
Notes
Notes Starting in Firefox 74, toSource() is no longer available for use by web content. It is still allowed for internal and privileged code.
IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoFirefox Android Full support 4Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support Nonodejs No support No
toStringChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support 5Safari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support 10.1Safari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes
unicodeChrome Full support 50Edge Full support 12
Notes
Full support 12
Notes
Notes Case folding is implemented in version 13
Firefox Full support 46IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 46Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support Yes
@@matchChrome Full support 50Edge Full support 13Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0
@@matchAllChrome Full support 73Edge Full support 79Firefox Full support 67IE No support NoOpera Full support 60Safari Full support 13WebView Android Full support 73Chrome Android Full support 73Firefox Android Full support 67Opera Android Full support 52Safari iOS Full support 13Samsung Internet Android Full support 5.0nodejs Full support 12.0.0
@@replaceChrome Full support 50Edge Full support 79Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0
@@searchChrome Full support 50Edge Full support 13Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0
@@speciesChrome Full support 50Edge Full support 13Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.5.0
Full support 6.5.0
Full support 6.0.0
Disabled
Disabled From version 6.0.0: this feature is behind the --harmony runtime flag.
@@splitChrome Full support 50Edge Full support 79Firefox Full support 49IE No support NoOpera Full support 37Safari Full support 10WebView Android Full support 50Chrome Android Full support 50Firefox Android Full support 49Opera Android Full support 37Safari iOS Full support 10Samsung Internet Android Full support 5.0nodejs Full support 6.0.0

Legend

Full support  
Full support
No support  
No support
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.
Deprecated. Not for use in new websites.
Deprecated. Not for use in new websites.
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.

Firefox-specific notes

Starting with Firefox 34, 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).

See also