Character Classes and Ranges

Understanding Character Classes

Character classes allow you to define a set of characters to match. They are enclosed in square brackets [ ]. Any single character within the brackets will match. For example, [abc] will match any occurrence of ‘a’, ‘b’, or ‘c’.

javascript

	const regex = /[abc]/;
	console.log(regex.test('apple')); // true (matches 'a')
	console.log(regex.test('banana')); // true (matches 'a')
	console.log(regex.test('cherry')); // true (matches 'c')
	console.log(regex.test('date')); // false (no match)

Using Ranges within Character Classes

Ranges allow you to specify a range of characters using a hyphen -. For example, [a-z] matches any lowercase letter from ‘a’ to ‘z’.

javascript

	const regex = /[a-z]/;
	console.log(regex.test('apple')); // true (matches 'a')
	console.log(regex.test('Banana')); // true (matches 'a', 'n')
	console.log(regex.test('12345')); // false (no match)

You can combine ranges and individual characters within a single character class:

javascript

	const regex = /[a-zA-Z0-9]/;
	console.log(regex.test('apple')); // true (matches 'a')
	console.log(regex.test('Banana')); // true (matches 'B')
	console.log(regex.test('12345')); // true (matches '1')
	console.log(regex.test('!@#$%')); // false (no match)

Predefined Character Classes

JavaScript provides several predefined character classes for common sets of characters:

\d : Matches any digit (equivalent to [0-9])
\D : Matches any non-digit
\w : Matches any word character (alphanumeric + underscore, equivalent to [a-zA-Z0-9_])
\W : Matches any non-word character
\s : Matches any whitespace character (space, tab, newline)
\S : Matches any non-whitespace character

javascript

	const regexDigit = /\d/;
	console.log(regexDigit.test('123')); // true (matches '1')
	console.log(regexDigit.test('abc')); // false (no match)
	
	const regexNonDigit = /\D/;
	console.log(regexNonDigit.test('123')); // false (no match)
	console.log(regexNonDigit.test('abc')); // true (matches 'a')
	
	const regexWord = /\w/;
	console.log(regexWord.test('hello_world123')); // true (matches 'h')
	console.log(regexWord.test('!@#$%')); // false (no match)
	
	const regexWhitespace = /\s/;
	console.log(regexWhitespace.test('hello world')); // true (matches space)
	console.log(regexWhitespace.test('helloworld')); // false (no match)

Exercises

Write a regular expression that matches any lowercase letter.
Create a Regex pattern that matches any digit and any uppercase letter.
Write a regular expression that matches any non-word character.

Character classes and ranges are powerful tools for defining sets of characters in your patterns.