Regex Cheat Sheet

Testing a regex

Use the .test() method

const testString = 'My test string'
const testRegex = /string/
testRegex.test(testString)

Testing multiple patterns

Use the OR operator (|)

const regex = /yes|no|maybe/

Ignoring case

Use the i flag for case insensitivity

const caseInsensitiveRegex = /ignore case/i
const testString = 'We use the i flag to iGnOrE CasE'
caseInsensitiveRegex.test(testString) // true

Extracting the first match to a variable

Use the .match() function

const match = 'Hello World!'.match(/hello/i) // 'Hello'

Extracting all of the matches in an array

Use the g flag

const testString = 'Repeat repeat rePeAT'
const regexWithAllMatches = /Repeat/gi
testString.match(regexWithAllMatches) // ['Repeat', 'repeat', 'rePeAT']

Matching any character

Use the wildcard character . to be a placeholder for any character

// To match 'cat', 'BAT', 'fAT', 'mat'
const regexWithWildcard = /.at/gi
const testString = 'cat BAT cupcake fAT mat dog'
const allMatchingWords = testString.match(regexWithWildcard) // ['cat', 'BAT', 'fAT', 'mat']

Matching a single character with multiple possibilities

Use character classes, which allow you to define a group of characters you wish to match
You place them inside square brackets []

// Match 'cat' 'fat' and 'mat' but not 'bat'
const regexWithCharClass = /[cfm]at/g
const testString = 'cat fat bat mat'
const allMatchingWords = testString.match(regexWithCharClass) // ['cat', 'fat', 'mat']

Match letters of the alphabet

Use a range within the character set [a-z]

const regexWithCharRange = /[a-e]at/
const catString = 'cat'
const batString = 'bat'
const fatString = 'fat'

regexWithCharRange.test(catString) // true
regexWithCharRange.test(batString) // true
regexWithCharRange.test(fatString) // false

Match specific numbers and letters

You can also use the hyphen to match numbers

const regexWithLetterAndNumberRange = /[a-z0-9]/ig
const testString = 'Victor5'
testString.match(regexWithLetterAndNumberRange) // true

Match a single, unknown character

To match a set of characters you don't want to have, use the negated character set
To negate a character set, use a caret ^

const allCharsNotVowels = /[^aeiou]/gi
const allCharsNotVowelsOrNumbers = /[^aeiou0-9]/gi

Match characters that occur one or more times in a row

Use the + symbol

const oneOrMoreAsRegex = /a+/gi
const oneOrMoreSsRegex = /s+/gi
const cityInFlorida = 'Tallahassee'

cityInFlorida.match(oneOrMoreAsRegex) // ['a', 'a', 'a']
cityInFlorida.match(oneOrMoreSsRegex) // ['ss']

Matches characters that occur zero or more times in a row

Use the asterisk *

const zeroOrMoreOsRegex = /hi*/gi
const normalHi = 'hi'
const happyHi = 'hiiiiii'
const twoHis = 'hiihii'
const bye = 'bye'

normalHi.match(zeroOrMoreOsRegex) // ['hi']
happyHi.match(zeroOrMoreOsRegex) // ['hiiiiii']
twoHis.match(zeroOrMoreOsRegex) // ['hii', 'hii']
bye.match(zeroOrMoreOsRegex) // null

Lazy Matching

The smallest part of a string that matches the given requirements
Regex, by default, are greedy (matches the longest portion of a string meeting the given requirements)
Use the ? character to lazy match

const testString = 'catastrophe'
const greedyRexex = /c[a-z]*t/gi
const lazyRegex = /c[a-z]*?t/gi

testString.match(greedyRexex) // ['catast']
testString.match(lazyRegex) // ['cat']

Match starting string patterns

To test for a match of characters at the beginning of a string, use the caret ^, but outside of the character set

const emmaAtFrontOfString = 'Emma likes cats a lot.'
const emmaNotAtFrontOfString = 'The cats Emma likes are fluffy.'
const startingStringRegex = /^Emma/

startingStringRegex.test(emmaAtFrontOfString) // true
startingStringRegex.test(emmaNotAtFrontOfString) // false

Match ending string patterns

Use the dollar sign $ at the end of a regex to check whether a pattern exists at the end of a string

const emmaAtBackOfString = 'The cats do not like Emma'
const emmaNotAtBackOfString = 'Emma loves the cats'
const startingStringRegex = /Emma$/

startingStringRegex.test(emmaAtBackOfString) // true
startingStringRegex.test(emmaNotAtBackOfString) // false

Matching all letters and numbers

Use the \word shorthand

const longHand = /[A-Za-z0-9_]+/
const shortHand = /\w+/
const numbers = '42'
const myFavoriteColor = 'magenta'

longHand.test(numbers) // true
shortHand.test(numbers) // true
longHand.test(myFavoriteColor) // true
shortHand.test(myFavoriteColor) // true

Match everything except letters & numbers

You can use for the opposite of \w with \W

const noAlphaNumericCharRegex = /\W/gi
const weirdCharacters = '!_$!!'
const alphaNumericCharacters = 'ab283AD'

noAlphaNumericCharRegex.test(weirdCharacters) // true
noAlphaNumericCharRegex.test(alphaNumericCharacters) // false

Match all numbers

You can use a character set 0-9, or use the shorthand \d

const digitsRegex = /\d/g
const stringWithDigits = 'My cat eats $20.00 worth of food a week.'

stringWithDigits.match(digitsRegex) // ['2', '0', '0', '0']

Match all non-numbers

You can use the opposite of \d with \D

const nonDigitsRegex = /\D/g
const stringWithLetters = '101 degrees'

stringWithLetters.match(nonDigitsRegex) // [' ', 'd', 'e', 'g', 'r', 'e', 'e', 's']

Matching whitespace

Use \s to match white space and carriage returns

const sentenceWithWhitespace = 'I like cats!'
const spaceRegex = /\s/g
whiteSpace.match(sentenceWithWhitespace) // [' ', ' ']

Matching non-whitespace

You can use the opposite of \s with \S

const sentenceWithWhitespace = 'C a t'
const nonWhiteSpaceRegex = /\S/g
sentenceWithWhitespace.match(nonWhiteSpaceRegex) // ['C', 'a', 't']

Matching character counts

You can specify a specific number of characters in a row using {lowerBound, upperBound}

const regularHi = 'hi'
const mediocreHi = 'hiii'
const superExcitedHey = 'heeeeyyyyy!!!'
const excitedRegex = /hi{1,4}/

excitedRegex.test(regularHi) // true
excitedRegex.test(mediocreHi) // true
excitedRegex.test(superExcitedHey) // false

Matching lowest number of character counts

You can define only a minimum number of character requirements with {lowerBound,}
This is called a quantity specifier

const regularHi = 'hi'
const mediocreHi = 'hiii'
const superExcitedHey = 'heeeeyyyyy!!!'
const excitedRegex = /hi{2,}/

excitedRegex.test(regularHi) // false
excitedRegex.test(mediocreHi) // true
excitedRegex.test(superExcitedHey) // false

Matching an exact number of character counts

_ You can specify the exact number of character requirements with {requiredCount}

const regularHi = 'hi'
const bestHi = 'hii'
const mediocreHi = 'hiii'
const excitedRegex = /hi{2}/

excitedRegex.test(regularHi) // false
excitedRegex.test(bestHi) // true
excitedRegex.test(mediocreHi) // false

Matching all or none of a character

To check whether a character exists, use the ?

const britishSpelling = 'color'
const americanSpelling = 'Color'
const languageRegex = /colou?r/i

languageRegex.test(britishSpelling) // true
languageRegex.test(americanSpelling) // true