Regular expression cheat sheet

    • Testing regular expressions
    • Testing multiple modes
    • Ignore case
    • Extract the first match to the variable
    • Extracts all matches in the array
    • Match any character
    • There are many possibilities for matching a single role
    • Match the letter
    • Matches specific numbers and letters
    • Matches an unknown character
    • Matches characters that appear one or more times in a row
    • Matches characters that occur zero or more times in a row
    • Delayed match
    • Matches the start string pattern
    • Matches the ending string pattern
    • Matches all letters and numbers
    • Matches everything except letters and numbers
    • Match all numbers
    • Matches all non-numbers
    • Match the blank space
    • Match non-space
    • Number of matching characters
    • Minimum number of matched characters
    • The number of characters that match the exact number
    • Matches all or none of the characters

Regular expressions or “regex” are used to match parts of a string. Here’s the cheat sheet I used to create regular expressions.

Testing regular expressions

  • use.test()methods
let testString = "My test string";
let testRegex = /string/;
testRegex.test(testString);
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Testing multiple modes

  • Using the OR operator (|)
const regex = /yes|no|maybe/;
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Ignore case

  • The use of theiFlag to be case sensitive
const caseInsensitiveRegex = /ignore case/i;
const testString = 'We use the i flag to iGnOrE CasE';
caseInsensitiveRegex.test(testString); // true
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Extract the first match to the variable

  • use.match()function
const match = "Hello World!".match(/hello/i); // "Hello"
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Extracts all matches in the array

  • usegmark
const testString = "Repeat repeat rePeAT";
const regexWithAllMatches = /Repeat/gi;
testString.match(regexWithAllMatches); // ["Repeat", "repeat", "rePeAT"]
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Match any character

  • Use wildcards.As 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"]
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There are many possibilities for matching a single role

  • Use the character class, which allows you to define a set of characters that you want to match
  • You put them in 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"]
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Match the letter

  • 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
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Matches specific numbers and letters

  • You can also use a hyphen to match numbers
const regexWithLetterAndNumberRange = /[a-z0-9]/ig;
const testString = "Emma19382";
testString.match(regexWithLetterAndNumberRange) // true
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Matches an unknown character

  • To match an unwanted character set, use the reverse character set
  • To negate character sets, use caret^
const allCharsNotVowels = /[^aeiou]/gi;
const allCharsNotVowelsOrNumbers = /[^aeiou0-9]/gi;
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Matches characters that appear one or more times in a row

  • use+symbol
const oneOrMoreAsRegex = /a+/gi;
const oneOrMoreSsRegex = /s+/gi;
const cityInFlorida = "Tallahassee";

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

  • The smallest part of a string that meets a given requirement
  • By default, regular expressions are greedy (matching the longest part of a string that satisfies a given requirement)
  • use?Character for lazy matching
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"]
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Matches the start string pattern

  • To test for a match at the beginning of the string, use the caret^, but outside 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
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Matches the ending string pattern

  • $Use the dollar sign at the end of the regular expression to check for patterns at the end of the string
const emmaAtBackOfString = "The cats do not like Emma";
const emmaNotAtBackOfString = "Emma loves the cats";
const startingStringRegex = /Emma$/;

startingStringRegex.test(emmaAtBackOfString); // true
startingStringRegex.test(emmaNotAtBackOfString); // false
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Matches all letters and numbers

  • use\wordshorthand
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
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Matches everything except letters and numbers

  • You can use\wThe opposite of the\WUsed together
const noAlphaNumericCharRegex = /\W/gi;
const weirdCharacters = ! "" _ $!!!!!";
const alphaNumericCharacters = "ab283AD";

noAlphaNumericCharRegex.test(weirdCharacters); // true
noAlphaNumericCharRegex.test(alphaNumericCharacters); // false
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Match all numbers

  • You can use character sets[0-9]You can also use 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"]
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Matches all non-numbers

  • You can use\dThe opposite of the\DUsed together
const nonDigitsRegex = /\D/g;
const stringWithLetters = "101 degrees";

stringWithLetters.match(nonDigitsRegex); // [" ", "d", "e", "g", "r", "e", "e", "s"]
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Match the blank space

  • use\sMatches Spaces and carriage returns
const sentenceWithWhitespace = "I like cats!"
var spaceRegex = /\s/g;
whiteSpace.match(sentenceWithWhitespace); // [" ", ""]
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Match non-space

  • You can use\sThe opposite of the\SUsed together
const sentenceWithWhitespace = "C a t"
const nonWhiteSpaceRegex = /\S/g;
sentenceWithWhitespace.match(nonWhiteSpaceRegex); // ["C", "a", "t"]
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Number of matching characters

  • You can use it to specify a specific number of characters in a line{lowerBound, upperBound}
const regularHi = "hi";
const mediocreHi = "hiii";
const superExcitedHey = "heeeeyyyyy!!!";
const excitedRegex = {1, 4} / / hi;

excitedRegex.test(regularHi); // true
excitedRegex.test(mediocreHi); // true
excitedRegex.test(superExcitedHey); //false
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Minimum number of matched characters

  • You can only define the minimum number of character requirements using the following command{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
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The number of characters that match the exact number

  • You can specify the exact number of characters required using the following command{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
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Matches all or none of the characters

  • To check if a character exists, use the?
const britishSpelling = "colour";
const americanSpelling = "Color";
const languageRegex = /colou? r/i;

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