regexp

A regular expression object, or any object that has aSymbol.match method.

Ifregexp is not aRegExp object and does not have aSymbol.match method, it is implicitly converted to aRegExp by usingnew RegExp(regexp).

If you don't give any parameter and use thematch() method directly, you will get anArray with an empty string:[""], because this is equivalent tomatch(/(?:)/).

AnArray whose contents depend on the presence or absence of the global (g) flag, ornull if no matches are found.

• If theg flag is used, all results matching the complete regular expression will be returned, but capturing groups are not included.
• If theg flag is not used, only the first complete match and its related capturing groups are returned. In this case,match() will return the same result asRegExp.prototype.exec() (an array with some extra properties).

The implementation ofString.prototype.match doesn't do much other than calling theSymbol.match method of the argument with the string as the first parameter. The actual implementation comes fromRegExp.prototype[Symbol.match]().

• If you need to know if a string matches a regular expressionRegExp, useRegExp.prototype.test().
• If you only want the first match found, you might want to useRegExp.prototype.exec() instead.
• If you want to obtain capture groups and the global flag is set, you need to useRegExp.prototype.exec() orString.prototype.matchAll() instead.

For more information about the semantics ofmatch() when a regex is passed, seeRegExp.prototype[Symbol.match]().

In the following example,match() is used to find"Chapter" followed by one or more numeric characters followed by a decimal point and numeric character zero or more times.

The regular expression includes thei flag so that upper/lower case differences will be ignored.

const str = "For more information, see Chapter 3.4.5.1";const re = /see (chapter \d+(\.\d)*)/i;const found = str.match(re);console.log(found);// [//   'see Chapter 3.4.5.1',//   'Chapter 3.4.5.1',//   '.1',//   index: 22,//   input: 'For more information, see Chapter 3.4.5.1',//   groups: undefined// ]

In the match result above,'see Chapter 3.4.5.1' is the whole match.'Chapter 3.4.5.1' was captured by(chapter \d+(\.\d)*).'.1' was the last value captured by(\.\d). Theindex property (22) is the zero-based index of the whole match. Theinput property is the original string that was parsed.

The following example demonstrates the use of the global flag and ignore-case flag withmatch(). All lettersA throughE anda throughe are returned, each its own element in the array.

const str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";const regexp = /[a-e]/gi;const matches = str.match(regexp);console.log(matches);// ['A', 'B', 'C', 'D', 'E', 'a', 'b', 'c', 'd', 'e']

In browsers which support named capturing groups, the following code captures"fox" or"cat" into a group namedanimal:

const paragraph = "The quick brown fox jumps over the lazy dog. It barked.";const capturingRegex = /(?<animal>fox|cat) jumps over/;const found = paragraph.match(capturingRegex);console.log(found.groups); // {animal: "fox"}

If an object has aSymbol.match method, it can be used as a custom matcher. The return value ofSymbol.match becomes the return value ofmatch().

const str = "Hmm, this is interesting.";str.match({  [Symbol.match](str) {    return ["Yes, it's interesting."];  },}); // returns ["Yes, it's interesting."]

When theregexp parameter is a string or a number, it is implicitly converted to aRegExp by usingnew RegExp(regexp).

const str1 =  "All numbers except NaN satisfy <= Infinity and >= -Infinity in JavaScript.";const str2 =  "My grandfather is 65 years old and My grandmother is 63 years old.";const str3 = "The contract was declared null and void.";str1.match("number"); // "number" is a string. returns ["number"]str1.match(NaN); // the type of NaN is the number. returns ["NaN"]str1.match(Infinity); // the type of Infinity is the number. returns ["Infinity"]str1.match(-Infinity); // returns ["-Infinity"]str2.match(65); // returns ["65"]str3.match(null); // returns ["null"]

This may have unexpected results if special characters are not properly escaped.

console.log("123".match("1.3")); // [ "123" ]

This is a match because. in a regex matches any character. In order to make it only match specifically a dot character, you need to escape the input.

console.log("123".match("1\\.3")); // null

• Polyfill ofString.prototype.match incore-js with fixes and implementation of modern behavior likeSymbol.match support
• Regular expressions guide
• String.prototype.matchAll()
• RegExp
• RegExp.prototype.exec()
• RegExp.prototype.test()