RegExp

Baseline *

20157

RegExp

JavaScript

RegExp 2

2 2
RegExp 2

const re = /ab+c/i; // 
// 
const re = new RegExp("ab+c", "i"); // 
// 
const re = new RegExp(/ab+c/, "i"); //

RegExp new RegExp('ab+c')

RegExp()

new RegExp(/ab+c/, flags) RegExp 1 2

\

const re = /\w+/;
// 
const re = new RegExp("\\w+");

: RegExp

x

x
x[Symbol.match] undefined
x[Symbol.match] undefined x RegExp x RegExp Symbol.match

Symbol.match

RegExp Symbol.match undefined exec [Symbol.replace]()
RegExp Symbol.match

[Symbol.match]() exec

String.prototype.endsWith(), startsWith(), includes() TypeError
String.prototype.matchAll() replaceAll() global [Symbol.matchAll]() [Symbol.replace]()
RegExp() pattern pattern pattern pattern source flags

String.prototype.endsWith()

"foobar".endsWith({ toString: () => "bar" }); // true
"foobar".endsWith(/bar/); // TypeError: First argument to String.prototype.endsWith must not be a regular expression

[Symbol.match] undefined String.prototype.match() [Symbol.match] match() re.toString() 2 RegExp

const re = /bar/g;
re[Symbol.match] = false;
"/bar/g".endsWith(re); // true
re.exec("bar"); // [ 'bar', index: 0, input: 'bar', groups: undefined ]
"bar & bar".replace(re, "foo"); // 'foo & foo'

Perl RegExp

RegExp Perl Perl JavaScript RegExp

RegExp(): RegExp

RegExp.$1, , RegExp.$9
RegExp.input ($_)
RegExp.lastMatch ($&)
RegExp.lastParen ($+)
RegExp.leftContext ($`)
RegExp.rightContext ($')
RegExp[Symbol.species]

RegExp.escape(): RegExp()

RegExp.prototype RegExp

RegExp.prototype.constructor: RegExp RegExp
RegExp.prototype.dotAll: .
RegExp.prototype.flags: RegExp
RegExp.prototype.global
RegExp.prototype.hasIndices
RegExp.prototype.ignoreCase
RegExp.prototype.multiline
RegExp.prototype.source
RegExp.prototype.sticky: (sticky)
RegExp.prototype.unicode: Unicode
RegExp.prototype.unicodeSets: u v

RegExp

lastIndex

RegExp.prototype.compile(): ()
RegExp.prototype.exec()
RegExp.prototype.test()
RegExp.prototype.toString(): Object.prototype.toString()
RegExp.prototype[Symbol.match]()
RegExp.prototype[Symbol.matchAll]()
RegExp.prototype[Symbol.replace]()
RegExp.prototype[Symbol.search]()
RegExp.prototype[Symbol.split]()

String.prototype.replace() ,

$1 $2

const re = /(\w+)\s(\w+)/;
const str = "Maria Cruz";
const newStr = str.replace(re, "$2, $1");
console.log(newStr);

"Cruz, Maria"

//

(UnixWindows )

const text = "Some text\nAnd some more\r\nAnd yet\nThis is the end";
const lines = text.split(/\r?\n/);
console.log(lines); // [ 'Some text', 'And some more', 'And yet', 'This is the end' ]

. s dotAll

const s = "Please yes\nmake my day!";

s.match(/yes.*day/);
// null 

s.match(/yes.*day/s);
// Returns ["yes\nmake my day"]

sticky

sticky sticky RegExp.prototype.lastIndex

const str = "#foo#";
const regex = /foo/y;

regex.lastIndex = 1;
regex.test(str); // true
regex.lastIndex = 5;
regex.test(str); // false (sticky  lastIndex )
regex.lastIndex; // 0 ()

sticky global

sticky y lastIndex global g lastIndex

const re = /\d/y;
let r;
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
//   ...

global g 3 6

Unicode

\w \W ASCII a z A Z 0 9 _

ASCII \uHHHH HHHH 16 Unicode

Unicode

const text = " text   ";
const regex = /[\u0400-\u04ff]+/g;

const match = regex.exec(text);
console.log(match[0]); // ''
console.log(regex.lastIndex); // 7

const match2 = regex.exec(text);
console.log(match2[0]); // '' ('text' )
console.log(regex.lastIndex); // 15

//

Unicode \p{scx=Cyrl} \p{L}/u

URL

const url = "http://xxx.domain.com";
console.log(/^https?:\/\/(.+?)\./.exec(url)[1]); // 'xxx'

: URL URL API URL

const breakfasts = ["bacon", "eggs", "oatmeal", "toast", "cereal"];
const order = "Let me get some bacon and eggs, please";

order.match(new RegExp(`\\b(${breakfasts.join("|")})\\b`, "g"));
// ['bacon', 'eggs']


ECMAScript 2027 LanguageSpecification # sec-regexp-regular-expression-objects

Firefox

Firefox 34 undefined

// Firefox 33 
"x".replace(/x(.)?/g, (m, group) => {
  console.log(`group: ${JSON.stringify(group)}`);
});
// group: ""

// Firefox 34 
"x".replace(/x(.)?/g, (m, group) => {
  console.log(`group: ${group}`);
});
// group: undefined

RegExp.$N undefined ( 1053944)

MDN

MDN 20251110

GitHub