Character classes

JavaScript course · Intermediate · Lesson 119/134

Learn to narrow patterns with character classes like \d, \w and \s.

Character classes

A character class matches a whole set of characters with a single token. Built-in classes: \d digit, \w letter-digit-underscore, \s whitespace. You can also write your own with square brackets: [aeiou] matches one vowel.

/[aeiou]/.test("hello"); // true

Classes narrow your pattern and make the search precise. For example you can check that a field holds only digits with \d.

Negated classes

Every character class has an uppercase negated partner: \D matches a non-digit, \W a non-word character, \S a non-whitespace character.

"a5!".replace(/\D/g, ""); // "5"

This lets you do "remove everything that is not a digit" in one pattern. Negated classes are handy for targeting the characters you do not want.

Exercise Check whether a digit is present

Assign a regex literal that matches a digit to hasDigit. Then test it on the string "abc5def" with .test() and log the result with console.log.

Show example solution

/\d/.
Example solution:
let hasDigit = /\d/;
console.log(hasDigit.test("abc5def"));

Test yourself

Which pattern matches a digit?
- /\w/
- /\s/
- /\d/
- /d/
Show answer

/\d/ — Correct! /\d/ matches a digit from 0 to 9.

Match a whitespace character

const space = ____;
console.log(space.test("a b"));

Show answer

const space = /\s/;
console.log(space.test("a b"));

Match classes with their meaning

\d

digit
\w

letter/digit/_
\s

whitespace
\D

non-digit

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Character classes