/RegEx-Cheatsheet

Regular Expressions in JavaScript

RegEx Cheatsheet - Regular Expressions in JavaScript

Regex (Regular Expressions) are a way to search through a string of text in an advanced way

https://regexr.com/ for practice and reference

https://regexone.com/lesson/introduction_abcs

https://www.debuggex.com/cheatsheet/regex/javascript

https://regexcrossword.com/

https://youtu.be/rhzKDrUiJVk to follow along

Format

starts with / ends with / everything contained within this is the regEx

Counting and Special Character Selectors

  • e+ search for multiple strings of e i.e. ee or eee etc.
  • e+a? search for multiple strings of e and optionally search for a
  • re* search for multiple strings of r and optionally search for zero or more e's
  • /.at/ or . matches anything i.e. fat cat and eat, but will not match a new line
  • use \ to "escape" special characters \@
  • \w to match any word character
  • \W to match any non-word character
  • \s to match any form of white space
  • \S to match any form of non-white space
  • \w{4} matches any word that is {4}characters
  • \w{4,} matches any word that is {4} or more characters
  • \w{4,5} matches any word that is {4,} to {5}characters

Range Selectors

  • /[fc]at/ any three letter at word that starts with f or c i.e. fat or cat
  • /[a-z]at/ starts with any letter in the range of a to z and ends with at i.e. fat cat and eat
    • [a-z]
    • [A-Z]
    • [0-9]
    • [a-f]

Capture Group Selectors

  • \(t|T)he\g match the or The
  • \(t|e|r){2,3}\.\g matches between 2 to 3 of the characters t e or r then a .
  • /^The/ matches the beginning of the line only
  • /.\$/ match the end of our statement

Look-aheads and Look-behinds

  • /(?<=[tT]he)./g positive look-behind, returns the characters behind the or The, but doesn't actually capture the character
  • /(?<T[tT]he)./g negative look-behind, returns everything that doesn't follow behind the or The
  • /(?=at)./g positive look-ahead, returns anything that has an at after it
  • /(?!at)./g look-ahead, returns anything that doesn't have an at after it

Flags

after the end / you can add flags

  • /g or global allows you to match anywhere in the string(multiple matches vs first match)
  • /i case insensitive
  • /m multiline

const reg = /e+/g
const sentence = 
"The fat cat ran down the street.  
It was searching for a mouse to eat."

reg.test(sentence)

Phone Number Example

let isPhoneNumber = /\d{10}/g
let phoneNumber = 1234567890
isPhoneNumber.test(phoneNumber)

isPhoneNumber = /\d{3}-?\d{3}-?\d{4}/g
phoneNumber = "123-456-7890"
isPhoneNumber.test(phoneNumber)

isPhoneNumber = /\d{3}[ -]?\d{3}[ -]?\d{4}/g
phoneNumber = "123 456 7890"
isPhoneNumber.test(phoneNumber)

Captures digits of phone number

/(\d{3})[ -]?(\d{3})[ -]?\(d{4})/gm

Returns group 1,2, and 3

$1$2$3

change group 1's name to areacode

/(?<areacode>\d{3})[ -]?(\d{3})[ -]?\(d{4})/gm

phoneNumber = "(123) 456-7890"
/\?(?<areacode>\d{3}\)?[ -]?(\d{3})[ -]?\(d{4})/gm

phoneNumber = "+ 1 123 456-7890"
/((\+1)[ -])?\?(?<areacode>\d{3}\)?[ -]?(\d{3})[ -]?\(d{4})/gm

Email Example

const emailRegex = /\S+@\S+\.\S+/
const validEmail = "valid@gmail.com"
const fauxEmail = "invalid,con"
emailRegex.test(validEmail)
emailRegex.test(fauxEmail)

Credit Card Example

// const creditCardRegex = //g
const validCreditCard = "1234 5678 9101 1123"
const fauxCreditCard = "abcd 0000 fake 1111 card 2222"
// emailRegex.test(validEmail)
// emailRegex.test(fauxEmail)

Currency Example

Implement a function that will determine if a string represents a valid currency amount Such strings will have the following properties:

  • The amount must consist of base-10 digits
  • The amount may optionally contain thousands separators using the ',' character.
  • If thousands separators are present, they must be present at each thousands increment.
  • The amount must be prefixed by the currency symbol. We support US Dollars ($), Euros (€), and Japanese Yen (¥) only.
  • Negative amounts may be indicated either by a negative sign before the currency symbol or by enclosing the amount (including currency symbol) in parentheses, such as ($450)
  • Dollar and Euro amounts may contain an amount of cents, represented to exactly two digits of precision.
  • If a decimal point is present, the cents must be specified
  • Yen amounts may not contain decimal points
    • Amounts may not contain a leading zero, unless it is zero Dollars or Euros and cents are specified
  • Any other characters, including leading or trailing whitespace, is invalid
const currencyRegex = /[\$\€\¥][0-9]{1,3}(?:,?[0-9]{3})*(\.[0-9]{2}$)?/
    
currencyRegex.test('$450')//true
currencyRegex.test('-€23')//true
currencyRegex.test('(¥2400)')//true
currencyRegex.test('$4,500.00')//true
currencyRegex.test('€0.25')//true

currencyRegex.test('cat')//false
currencyRegex.test('£25')//false
currencyRegex.test('$45,0')//false*
currencyRegex.test('€350')//false*
currencyRegex.test('(-3.50)')//false
currencyRegex.test('¥120.00')//false*