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 RegExp 생성자는 특정 패턴에 맞는 텍스트를 위한 일반적인 표현식(regular expression object)을 만들어 냅니다.

정규 표현식에 대한 소개는 JavaScript Guide의 Regular Expressions chapter를 참조하시기 바랍니다.

Constructor

그냥 문자로 표기해서 생성할수도 있고, 생성자로 만들수도 있습니다.:

/pattern/flags         //문자표기방식
new RegExp(pattern[, flags])       //생성자로 만들때

Parameters

pattern
정규식(regular expression)을 나타내는 문자입니다..
flags

If specified, flags can have any combination of the following values:

g
global match; 일치하는 첫 번째 문자에서 멈추지 않고 전체에서 일치하는 모든 문자를 검색합니다.
i
ignore case(대소문자를 구별하지 않습니다.)
m
multiline; 시작 혹은 끝 문자 탐색(^ and $)이 다중행에 적용되도록 합니다.  (예로,  \n 혹은 \r로 개행된 각각의 라인 시작 혹은 끝 뿐만 아니라, 전체 입력 문자의 시작 혹은 끝에서 일치합니다.
y
sticky; matches only from the index indicated by the lastIndex property of this regular expression in the target string (and does not attempt to match from any later indexes).

Description

 

RegExp object만드는 2가지 방법:

1) 리터럴 방식 : 파라미터에 따옴표를 사용해선 안된다.   

2) 생성자 방식 : 파라미터에 따옴표를 사용 해야 한다. 

아래의 코드는 동일한 결과를 가진다.

/ab+c/i;
new RegExp('ab+c', 'i');
new RegExp(/ab+c/, 'i');

리터럴 방식은 이 expression이 evaluate될 때 regular expression의 컴파일 된(compilation of the regular expression) 형태를 제공한다. 그러니까 이 방식은 regular expression이 상수 형태일때 변하지 않을 때 쓴다. 예를들어 문자로 쓰는 regular expression을 반복문 안에서 쓰면 이것은 반복문을 돌 때마다 계속 다시 컴파일 되는 것이 아니라서  컴퓨터 자원을 낭비하지 않는다

생성자 방식으로 regular expression object 쓰는것은 , ex) new RegExp('ab+c'), regular expression이 런타임 방식으로 컴파일 되게 한다. regular expression패턴이 계속 변한다거나 아니면 regular expression 패턴이 어떻게 될지 모를때(예를 들어 패턴을 user input처럼 다른 곳에서 받아올때) 이 방식을 쓴다.

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:

var re = /\w+/;
var re = new RegExp('\\w+');

정규 표현식에서 특별한 의미를 갖는 문자들

Character Classes
Character Meaning
.

(The dot, the decimal point) 행 종결자(\n, \r, \u2028 or \u2029)를 제외한 임의의 1자와 일치합니다.

Inside character class, the dot loses its special meaning and matches a literal dot.

다중행 플래그(m)가 이 문자의 의미를 바꾸지 않는다는 점을 알아두십시오. 때문에 여러 행에 걸쳐 패턴을 일치시키고자 하는 경우 개행문자를 포함한 임의의 1자와 일치하는 [^]가 사용될 수 있습니다(물론 구형 버전의 IE를 제외하고는).

예를 들어, /.y/ 는"my" 와 "ay"와 일치하지만, "yes make my day"의 "yes"와는 일치하지 않습니다.

\d

기본 라틴 알파벳의 숫자문자와 일치합니다. [0-9]와 동일.

예를 들어, /\d/ 혹은 /[0-9]/ 는 "B2 is the suite number"의 "2"와 일치합니다.

\D

기본 라틴 알파벳의 숫자문자를 제외한 문자와 일치합니다. [^0-9]와 동일.

예를 들어, /\D/ 혹은 /[^0-9]/는 "B2 is the suite number"의 "B"와 일치합니다.

\w

Matches any alphanumeric character from the basic Latin alphabet, including the underscore. Equivalent to [A-Za-z0-9_].

For example, /\w/ matches "a" in "apple", "5" in "$5.28", and "3" in "3D".

\W

Matches any character that is not a word character from the basic Latin alphabet. Equivalent to [^A-Za-z0-9_].

For example, /\W/ or /[^A-Za-z0-9_]/ matches "%" in "50%".

\s

Matches a single white space character, including space, tab, form feed, line feed and other Unicode spaces. Equivalent to [ \f\n\r\t\v​\u00a0\u1680​\u180e\u2000​-\u200a​\u2028\u2029\u202f\u205f​\u3000\ufeff].

For example, /\s\w*/ matches " bar" in "foo bar".

\S

Matches a single character other than white space. Equivalent to [^ \f\n\r\t\v​\u00a0\u1680​\u180e\u2000​-\u200a​\u2028\u2029\u202f\u205f​\u3000\ufeff].

For example, /\S\w*/ matches "foo" in "foo bar".

\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 X is a letter from A - Z. Matches a control character in a string.

For example, /\cM/ matches control-M in a string.

\xhh Matches the character with the code hh (two hexadecimal digits).
\uhhhh Matches the character with the Unicode value hhhh (four hexadecimal digits).
\

For characters that are usually treated literally, indicates that the next character is special and not to be interpreted literally.

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

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, /a*/ means match 0 or more "a"s. To match * literally, precede it with a backslash; for example, /a\*/ matches "a*".

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.

For example, [abcd] is the same as [a-d]. They match the "b" in "brisket" and the "c" in "chop".

[^xyz]

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.

For example, [^abc] is the same as [^a-c]. They initially match "o" in "bacon" and "h" in "chop".

Alternation
Character Meaning
x|y

Matches either x or y.

For example, /green|red/ matches "green" in "green apple" and "red" in "red apple".

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, /^A/ does not match the "A" in "an A", but does match the first "A" in "An A".

$

Matches end of input. If the multiline flag is set to true, also matches immediately before a line break character.

For example, /t$/ does not match the "t" in "eater", but does match it in "eat".

\b

Matches a zero-width word boundary, such as between a letter and a space. (Not to be confused with [\b])

For example, /\bno/ matches the "no" in "at noon"; /ly\b/ matches the "ly" in "possibly yesterday".

\B

Matches a zero-width non-word boundary, such as between two letters or between two spaces.

For example, /\Bon/ matches "on" in "at noon", and /ye\B/ matches "ye" in "possibly yesterday".

Grouping and back references
Character Meaning
(x)

Matches x and remembers the match. These are called capturing groups.

For example, /(foo)/ matches and remembers "foo" in "foo bar". 

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 [1], ..., [n] or from the predefined RegExp object's properties $1, ..., $9.

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 n is a positive integer. A back reference to the last substring matching the n parenthetical in the regular expression (counting left parentheses).

For example, /apple(,)\sorange\1/ matches "apple, orange," in "apple, orange, cherry, peach". A more complete example follows this table.

(?: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, /bo*/ matches "boooo" in "A ghost booooed" and "b" in "A bird warbled", but nothing in "A goat grunted".

x+

Matches the preceding item x 1 or more times. Equivalent to {1,}.

For example, /a+/ matches the "a" in "candy" and all the "a"'s in "caaaaaaandy".

x*?
x+?

Matches the preceding item x like * and + from above, however the match is the smallest possible match.

For example, /".*?"/ matches '"foo"' in '"foo" "bar"' and does not match '"foo" "bar"' as without the ? behind the *.

x?

Matches the preceding item x 0 or 1 time.

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

If used immediately after any of the quantifiers *, +, ?, or {}, 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).

x{n}

Where n is a positive integer. Matches exactly n occurrences of the preceding item x.

For example, /a{2}/ 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".

x{n,}

Where n is a positive integer. Matches at least n occurrences of the preceding item x.

For example, /a{2,}/ doesn't match the "a" in "candy", but matches all of the a's in "caandy" and in "caaaaaaandy".

x{n,m}

Where n and m are positive integers. Matches at least n and at most m occurrences of the preceding item x.

For example, /a{1,3}/ 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.

Assertions
Character Meaning
x(?=y)

Matches x only if x is followed by y.

For example, /Jack(?=Sprat)/ matches "Jack" only if it is followed by "Sprat".
/Jack(?=Sprat|Frost)/ matches "Jack" only if it is followed by "Sprat" or "Frost". However, neither "Sprat" nor "Frost" is part of the match results.

x(?!y)

Matches x only if x is not followed by y.

For example, /\d+(?!\.)/ matches a number only if it is not followed by a decimal point.
/\d+(?!\.)/.exec('3.141') matches "141" but not "3.141".

Properties

RegExp.prototype
Allows the addition of properties to all objects.
RegExp.length
The value of RegExp.length is 2.
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.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[@@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.

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

This example demonstrates how one could use the sticky flag on regular expressions to match individual lines of multiline input.

var text = 'First line\nSecond line';
var regex = /(\S+) line\n?/y;

var match = regex.exec(text);
console.log(match[1]);        // logs 'First'
console.log(regex.lastIndex); // logs '11'

var match2 = regex.exec(text);
console.log(match2[1]);       // logs 'Second'
console.log(regex.lastIndex); // logs '22'

var match3 = regex.exec(text);
console.log(match3 === null); // logs 'true'

One can test at run-time whether the sticky flag is supported, using try { … } catch { … }. For this, either an eval(…) expression or the RegExp(regex-string, flags-string) syntax must be used (since the /regex/flags notation is processed at compile-time, so throws an exception before the catch block is encountered). For example:

var supports_sticky;
try { RegExp('', 'y'); supports_sticky = true; }
catch(e) { supports_sticky = false; }
console.log(supports_sticky); // logs 'true'

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.

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
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
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).

See also

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