Skip to main content

JavaScript Regular Expressions (RegEx) Cheatsheet

JavaScript uses RegExp objects to work with regular expressions for searching and manipulating strings.

🧠 Syntax Basics

const pattern = /expression/flags;
const regex = new RegExp("expression", "flags");
FlagMeaning
gGlobal search (all matches)
iCase-insensitive
mMultiline mode
sDot matches newline
uUnicode
ySticky matching

🔍 Common RegEx Patterns

1. Match an Email Address

const regex = /^[\w.-]+@[a-zA-Z\d.-]+\.[a-zA-Z]{2,}$/;
  • Explanation: Matches user@domain.com
  • \w = word char, . = dot, - = hyphen

2. Match a URL

const regex = /https?:\/\/(www\.)?[a-zA-Z0-9-]+\.[a-zA-Z]{2,}(\/\S*)?/;
  • Matches http://, https://, optional www, domain, and optional path

3. Validate a Phone Number (US)

const regex = /^\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}$/;
  • Matches formats like (123) 456-7890, 123-456-7890, 1234567890

4. Match Only Digits

const regex = /^\d+$/;
  • Only digits (0-9), at least one

5. Match Only Letters

const regex = /^[a-zA-Z]+$/;
  • Only alphabetic characters

6. Check for Whitespace

const regex = /\s/;
  • Matches any whitespace character

7. Password Strength (8+ chars, upper, lower, number, special)

const regex = /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@#$%^&+=!]).{8,}$/;
  • Uses lookaheads to ensure character variety

8. Extract Numbers from a String

const regex = /\d+/g;
const numbers = "abc123def456".match(regex); // ['123', '456']

9. Detect HTML Tags

const regex = /<[^>]*>/g;
  • Matches any HTML tags like <div>, </p>, etc.

10. Match Dates (MM/DD/YYYY)

const regex = /^(0[1-9]|1[0-2])\/(0[1-9]|[12]\d|3[01])\/\d{4}$/;
  • Matches US-style dates like 04/16/2025

11. Match Hex Colors

const regex = /^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$/;
  • Matches hex colors like #fff or #12a3ef

12. Match Time (24-hour HH:MM)

const regex = /^([01]\d|2[0-3]):([0-5]\d)$/;
  • Matches times like 14:30, 09:45

🧪 Using RegEx in JavaScript

const pattern = /^\d{3}$/;
console.log(pattern.test("123")); // true
console.log("abc123".match(/\d+/g)); // ['123']

📌 Tips

  • Use RegExp.test() to check for a match (true/false)
  • Use String.match() to extract matches
  • Escape special characters like . or ? with \

Let me know if you'd like this exported to a .md file or extended with advanced patterns (e.g., IPv4, slugs, currency formats).

Back to top