Regex Cheatsheet

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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]/gi
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 = /\w+/
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/g
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 = 'colour'
const americanSpelling = 'Color'
const languageRegex = /colou?r/i

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

get all the numbers which contain . character and are preceded by $ character

(?<=$)[0-9\.]*

optionally match lowercase letter t or uppercase letter T, followed by letter h, followed by letter e. In parentheses we define positive lookahead which tells regular expression engine to match The or the which are followed by the word fat.

T|t]he(?=\sfat)

https://regex101.com/r/IDDARt/1

Negative Lookahead

get all The or the words from input string that are not followed by the word fat precedes by a space character.

[T|t]he(?!\sfat)

https://regex101.com/r/V32Npg/1

Negative Lookbehind

get all cat words from input string that are not after the word The or the

(?<!(T|t)he\s)(cat)

https://regex101.com/r/8Efx5G/1

Reference