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Regex matching JS ​

Regular expressions are their own prototype in JS - RegExp.

If you just want to match substrings inside another string:

js
// This has the global flag 'g' set to do multiple matches for a single string
const CAPITAL_LETTERS_PATTERN = /[A-Z]/g;

const fruits = "AppleBananaPomegranateOrange";

// ["A", "B", "P", "O"]
const matches = fruits.match(CAPITAL_LETTERS_PATTERN);

When to use which function ​

Stolen straight from MDN:

  • To know if a string matches (boolean), use .test()
  • To get a single match, use .exec()
  • To get multiple matches, use .match()
  • To get multiple matches using capture groups (the global flag must be set), use .exec() or .matchAll()

INFO

.matchAll() doesn't only return the matches, it instead returns an iterator containing the match and several other bits of information.

See String.prototype.match() - JavaScript | MDN See RegExp.prototype.test() - JavaScript | MDN

Regular expression flags ​

Regular expressions are of the form:

js
// Shorthand
const re = /pattern/flags;

// With the RegExp constructor
const re = new RegExp(pattern, flags);

Where flags is a sequence of none, one or more these flags:

  • d Generate indices for substring matches.
  • g Global search.
  • i Case-insensitive search.
  • m Makes ^ and $ match the start and end of each line instead of those of the entire string.
  • s Allows . to match newline characters.
  • u "Unicode"; treat a pattern as a sequence of Unicode code points.
  • v An upgrade to the u mode with more Unicode features.
  • y Perform a "sticky" search that matches starting at the current position in the target string.

(Yoinked directly from the MDN documentation)

Each flag also corresponds with a boolean property on the finished RegExp object. For example, g corresponds with RegExp.prototype.global:

js
const re = /hello-there/g;

console.log(re.global); // -> true

See Advanced searching with flags