Common Regex Patterns

Common Regex Patterns

Matching Email Addresses

A common use case for regular expressions is to validate email addresses. A typical email pattern requires a sequence of characters followed by an ”@” symbol, followed by another sequence of characters, a dot, and a domain.

	const regexEmail = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;
	
	// Examples:
	console.log(regexEmail.test('test@example.com')); // true
	console.log(regexEmail.test('user.name+tag+sorting@example.com')); // true
	console.log(regexEmail.test('user@subdomain.example.com')); // true
	console.log(regexEmail.test('invalid-email')); // false

Explanation:

• ^[a-zA-Z0-9._%+-]+ : Matches the user name part of the email, which can include letters, digits, dots, underscores, percent signs, plus signs, and hyphens.
• @ : Matches the ”@” symbol.
• [a-zA-Z0-9.-]+ : Matches the domain part of the email, which can include letters, digits, dots, and hyphens.
• \.[a-zA-Z]{2,}$ : Matches the top-level domain, which starts with a dot and includes at least two letters.

Matching URLs

Regex can also be used to validate URLs. A typical URL pattern requires a protocol (http, https), followed by ”://”, a domain name, and optionally a path.

	const regexURL = /^(https?:\/\/)?([a-zA-Z0-9.-]+)\.([a-zA-Z]{2,})(\/[a-zA-Z0-9.-]*)*\/?$/;
	
	// Examples:
	console.log(regexURL.test('http://example.com')); // true
	console.log(regexURL.test('https://www.example.com/path/to/page')); // true
	console.log(regexURL.test('example.com')); // true
	console.log(regexURL.test('ftp://invalid-url.com')); // false

Explanation:

• ^(https?:\/\/)? : Matches the protocol part (http or https), which is optional.
• ([a-zA-Z0-9.-]+) : Matches the domain name, which can include letters, digits, dots, and hyphens.
• \.([a-zA-Z]{2,}) : Matches the top-level domain, which starts with a dot and includes at least two letters.
• (\/[a-zA-Z0-9.-]*)*\/?$ : Matches the path part, which can include slashes, letters, digits, dots, and hyphens. The trailing slash is optional.

Matching Phone Numbers

Phone numbers can vary widely in format, but a common pattern is to match digits, optionally grouped by spaces, dots, or hyphens.

	const regexPhone = /^(\+?\d{1,3}[-.\s]?)?(\(?\d{3}\)?[-.\s]?)?\d{3}[-.\s]?\d{4}$/;
	
	// Examples:
	console.log(regexPhone.test('+1-800-555-1234')); // true
	console.log(regexPhone.test('(800) 555-1234')); // true
	console.log(regexPhone.test('800.555.1234')); // true
	console.log(regexPhone.test('5551234')); // true

Explanation:

• ^(\+?\d{1,3}[-.\s]?)? : Matches the optional country code, which may start with a ”+” and be followed by 1 to 3 digits. It can be separated by a hyphen, dot, or space.
• (\(?\d{3}\)?[-.\s]?)? : Matches the optional area code, which may be enclosed in parentheses and separated by a hyphen, dot, or space.
• \d{3}[-.\s]?\d{4}$ : Matches the local number part, which consists of 3 digits, followed by a hyphen, dot, or space, and then 4 digits.

Exercises

1. Write a regular expression to match a valid IP address.
2. Create a Regex pattern that matches a date in the format YYYY-MM-DD.
3. Write a regular expression to match hexadecimal color codes (e.g., #a3c113).

Common Regex patterns are incredibly useful for validating and extracting specific types of data.