Regular Expression Character Classes

In JavaScript, regular expressions (RegEx) allow you to match patterns in strings. Character classes are a fundamental concept that define a set of characters you want to match. They are enclosed in square brackets [] or use predefined shorthand notations for common patterns.

1. Basic Character Classes

Character classes let you match any one character from a specified set or range.

2. Negated Character Class

Use ^ inside brackets to negate the set. It matches any character not listed.

const regex = /[^0-9]/; // Matches any non-digit
console.log(regex.test("a")); // true
console.log(regex.test("5")); // false

3. Predefined Shorthand Character Classes

JavaScript provides shortcuts for commonly used character sets:

4. Dot . Character

• Matches any character except newline (\\n)
• Use the s flag to include newlines

const regex = /./;
console.log(regex.test("a")); // true
console.log(regex.test("\\n")); // false

5. Unicode Property Escapes (ES2018+)

For advanced Unicode matching, use \\p{...} with the u flag.

const emojiRegex = /\\p{Emoji}/u;
console.log(emojiRegex.test("😊")); // true

6. Combining Character Classes

You can combine ranges, negations, and shorthand classes in a single set:

const regex = /[A-Za-z\\d_]/; // Matches letters, digits, or underscore
console.log(regex.test('Z')); // true
console.log(regex.test('9')); // true
console.log(regex.test('-')); // false

7. Character Class Quantifiers

Character classes can be combined with quantifiers to match multiple occurrences:

8. Escaping Special Characters

Special characters like ., *, [, ] need to be escaped with \\ if you want to match them literally.

console.log("[test]".match(/[\[\]]/g)); // ["[", "]"]