regexCharacterClasses

Reports regex alternations that can be simplified to character classes.

✅ This rule is included in the ts stylisticStrict presets.

Character classes in regular expressions are more efficient than alternations because they don’t require backtracking. When multiple single-character alternatives are used in a regex pattern, they can be combined into a character class for better performance and readability.

Examples

❌ Incorrect

const pattern = /a|b|c/;

const digits = /1|2|3|4|5/;

const mixed = /a|b|[cd]/;

const withSets = /\w|\d|x/;

✅ Correct

const pattern = /[abc]/;

const digits = /[12345]/;

const mixed = /[abcd]/;

const withSets = /[\w\dx]/;

// Two alternatives are allowed (below the default threshold)
const twoChars = /a|b/;

// Multi-character alternatives cannot be simplified
const multiChar = /ab|cd/;

// Alternations with word boundaries or other assertions
const withBoundary = /a|b|c\b/;

Options

This rule is not configurable.

When Not To Use It

If you prefer the readability of explicit alternations over character classes, or if your codebase has specific conventions around regex formatting, you might prefer to disable this rule. Some developers find alternations easier to read when the alternatives represent distinct concepts rather than a set of characters.

Further Reading

• MDN: Regular expressions - Character classes
• MDN: Regular expressions - Disjunction

Equivalents in Other Linters

• ESLint: regexp/prefer-character-class