regexUnnecessaryNestedAssertions

Reports trivially nested assertions in regular expressions that can be simplified.

✅ This rule is included in the ts logical presets.

Regular expression lookarounds are trivially nested when it contains exactly one element that is itself an assertion (anchor or another lookaround of the same direction). Such lookarounds are unnecessary and can be simplified. This rule reports those lookarounds.

Examples

❌ Incorrect

const pattern = /(?=$)/;
const boundary = /(?=\b)/;

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

const pattern = new RegExp("(?=$)");
const boundary = RegExp("(?=\\b)");

✅ Correct

const pattern = /$/;
const boundary = /\b/;

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

const pattern = new RegExp("$");
const boundary = RegExp("\\b");

Options

This rule is not configurable.

When Not To Use It

If you intentionally keep nested regular expression structures for code clarity or documentation purposes, you might prefer to disable this rule.

Further Reading

• MDN: Lookahead and lookbehind assertions

Equivalents in Other Linters

• ESLint: regexp/no-trivially-nested-assertion