regexEmptyLookaroundsAssertions

Reports empty lookahead and lookbehind assertions in regular expressions.

✅ This rule is included in the ts logical presets.

Reports empty lookahead and lookbehind assertions in regular expressions. Empty lookarounds like (?=) or (?!) will trivially accept or reject all inputs since they match the empty string.

Examples

Empty Lookahead

❌ Incorrect

const pattern = /(?=)/;

✅ Correct

const pattern = /(?=\d)/;

Empty Negative Lookahead

❌ Incorrect

const pattern = /(?!)/;

✅ Correct

const pattern = /(?!\d)/;

Empty Lookbehind

❌ Incorrect

const pattern = /(?<=)/;

✅ Correct

const pattern = /(?<=\d)/;

Lookahead with Optional Content

❌ Incorrect

const pattern = /(?=a?)/;

✅ Correct

const pattern = /(?=a+)/;

Options

This rule is not configurable.

When Not To Use It

If you have a legitimate use case for empty lookarounds in generated or experimental regex patterns, you may disable this rule.

Further Reading

• MDN: Lookahead assertion
• MDN: Lookbehind assertion

Equivalents in Other Linters

• ESLint: regexp/no-empty-lookarounds-assertion