regexCharacterClassSetOperations

Reports lookarounds that can be replaced with character class set operations.

✅ This rule is included in the ts stylistic and stylisticStrict presets.

Regular expressions with the v flag have access to character class set operations like intersection (&&) and subtraction (--). These are more readable and performant than using lookarounds to achieve the same effect.

Examples

❌ Incorrect

// Negative lookahead can be subtraction
const pattern = /(?!\d)\w/v;
Error ts(1501)  ― This regular expression flag is only available when targeting 'es2024' or later.

// Positive lookbehind can be intersection
const pattern = /\w(?<=\d)/v;
Error ts(1501)  ― This regular expression flag is only available when targeting 'es2024' or later.

// Positive lookahead can be intersection
const pattern = /(?=\d)\w/v;
Error ts(1501)  ― This regular expression flag is only available when targeting 'es2024' or later.

✅ Correct

// Use subtraction instead of negative lookahead
const pattern = /[\w--\d]/v;
Error ts(1501)  ― This regular expression flag is only available when targeting 'es2024' or later.

// Use intersection instead of positive lookbehind
const pattern = /[\w&&\d]/v;
Error ts(1501)  ― This regular expression flag is only available when targeting 'es2024' or later.

// Use intersection instead of positive lookahead
const pattern = /[\w&&\d]/v;
Error ts(1501)  ― This regular expression flag is only available when targeting 'es2024' or later.

// Lookarounds without the v flag are valid
const pattern = /(?!\d)\w/;

// Complex lookarounds cannot be converted
const pattern = /(?!abc)\w/v;
Error ts(1501)  ― This regular expression flag is only available when targeting 'es2024' or later.

Options

This rule is not configurable.

When Not To Use It

If you prefer the explicit semantics of lookarounds over set operations, this rule might not be for you.

Further Reading

• MDN: Unicode character class escape - v-mode character class
• MDN: Lookahead assertion

Equivalents in Other Linters

• ESLint: regexp/prefer-set-operation