Regular Expressions Cheatsheet

Matches any single character in the brackets

/[aeiou]/.test('hello') // true

Matches any single character NOT in the brackets

/[^0-9]/.test('abc') // true

Matches any character in the specified range

/[A-Za-z]/.test('Hello') // true

Matches any single character except newline (unless s flag)

/h.t/.test('hat') // true

Matches alphanumeric character plus underscore [A-Za-z0-9_]

'hello_123'.match(/\w+/) // ['hello_123']

Matches any non-word character [^A-Za-z0-9_]

'hello world'.match(/\W/) // [' ']

Matches any digit [0-9]

'abc123'.match(/\d+/) // ['123']

Matches any non-digit character [^0-9]

'abc123'.match(/\D+/) // ['abc']

Matches any whitespace character (space, tab, newline)

'a b'.match(/\s/) // [' ']

Matches any non-whitespace character

'  hello  '.match(/\S+/) // ['hello']

Matches the start of string (or line with m flag)

/^hello/.test('hello world') // true

Matches the end of string (or line with m flag)

/world$/.test('hello world') // true

Matches a word boundary position

/\bcat\b/.test('the cat sat') // true

Matches a non-word boundary position

/\Bcat/.test('concat') // true

Matches 0 or more of the preceding token (greedy)

'aaa'.match(/a*/) // ['aaa']

Matches 0 or more of the preceding token (lazy)

'aaa'.match(/a*?/) // ['']

Matches 1 or more of the preceding token (greedy)

'aaa'.match(/a+/) // ['aaa']

Matches 1 or more of the preceding token (lazy)

'aaa'.match(/a+?/) // ['a']

Matches 0 or 1 of the preceding token (optional)

/colou?r/.test('color') // true

Matches 0 or 1 of the preceding token (lazy)

'a'.match(/a??/) // ['']

Matches exactly n occurrences of the preceding token

/\d{4}/.test('2024') // true

Matches n or more occurrences of the preceding token

'aaaa'.match(/a{2,}/) // ['aaaa']

Matches n or more occurrences (lazy)

'aaaa'.match(/a{2,}?/) // ['aa']

Matches between n and m occurrences (greedy)

'aaaaa'.match(/a{2,4}/) // ['aaaa']

Matches between n and m occurrences (lazy)

'aaaaa'.match(/a{2,4}?/) // ['aa']

Groups pattern and captures the match for backreference

'abc abc'.match(/(abc) \1/) // ['abc abc', 'abc']

Groups pattern without capturing the match

/(?:ab)+/.test('abab') // true

Groups pattern with a named reference

'2024-01-15'.match(/(?<year>\d{4})/).groups.year // '2024'

References the nth captured group

/(\w+) \1/.test('hello hello') // true

References a named captured group

/(?<word>\w+) \k<word>/.test('test test') // true

Matches if followed by pattern without consuming it

'100px'.match(/\d+(?=px)/) // ['100']

Matches if NOT followed by pattern

/\d+(?!px)/.test('100em') // true

Matches if preceded by pattern without consuming it

'$100'.match(/(?<=\$)\d+/) // ['100']

Matches if NOT preceded by pattern

/(?<!\$)\d+/.test('€100') // true

Matches either a or b

/cat|dog/.test('I have a dog') // true

Find all matches instead of stopping after first match

'abab'.match(/a/g) // ['a', 'a']

Makes the pattern case-insensitive

/hello/i.test('HELLO') // true

Makes ^ and $ match start/end of each line

/^b/m.test('a\nb') // true

Makes dot match newline characters as well

/a.b/s.test('a\nb') // true

Enables full Unicode matching and unicode escapes

/\p{Emoji}/u.test('😀') // true

Matches only from lastIndex position in target string

const re = /a/y; re.lastIndex = 1; re.test('bab') // true

Generate indices for substring matches

'abc'.match(/b/d).indices // [[1, 2]]

Returns true if pattern matches string

/\d+/.test('abc123') // true

Returns match array or null with detailed info

/(\d+)/.exec('abc123') // ['123', '123', index: 3]

Returns array of matches or null

'a1b2c3'.match(/\d/g) // ['1', '2', '3']

Returns iterator of all matches with groups (requires g flag)

[...'a1b2'.matchAll(/(\d)/g)] // detailed matches

Replaces first match (or all with g flag) with replacement

'hello'.replace(/l/g, 'L') // 'heLLo'

Replaces all matches (regex must have g flag)

'aaa'.replaceAll(/a/g, 'b') // 'bbb'

Returns index of first match or -1 if not found

'hello123'.search(/\d/) // 5

Splits string by regex matches into array

'a1b2c3'.split(/\d/) // ['a', 'b', 'c', '']

Replace using function that receives match details

'a1b2'.replace(/\d/g, m => m * 2) // 'a2b4'

Replace using captured group references

'John Smith'.replace(/(\w+) (\w+)/, '$2, $1') // 'Smith, John'