regexUnusedLazyQuantifiers

Reports lazy quantifiers that have no effect because the quantifier is constant.

✅ This rule is included in the ts logical presets.

When a regular expression quantifier has fixed bounds (min equals max), there is no choice in how many times to match, so the lazy modifier ? is irrelevant. This rule reports lazy quantifiers that have no effect because the quantifier matches a fixed number of times.

Examples

Fixed Count Quantifiers

❌ Incorrect

const pattern = /a{1}?/;
const pattern2 = /a{4}?/;
const pattern3 = /a{2,2}?/;

✅ Correct

const pattern = /a{1}/;
const pattern2 = /a{4}/;
const pattern3 = /a{2,2}/;

Groups and Character Classes

❌ Incorrect

const pattern = /(ab){2}?/;
const pattern2 = /[a-z]{3}?/;

✅ Correct

const pattern = /(ab){2}/;
const pattern2 = /[a-z]{3}/;

Variable Quantifiers (Valid)

These are valid because the quantifier is not constant:

const pattern = /a*?/; // min=0, max=Infinity
const pattern2 = /a+?/; // min=1, max=Infinity
const pattern3 = /a??/; // min=0, max=1
const pattern4 = /a{1,3}?/; // min=1, max=3
const pattern5 = /a{2,}?/; // min=2, max=Infinity

Options

This rule is not configurable.

When Not To Use It

If you prefer explicit lazy modifiers for documentation purposes, even when they have no effect, you might want to disable this rule.

Further Reading

• MDN: Quantifier
• MDN: Regular expressions

Equivalents in Other Linters

• ESLint: regexp/no-useless-lazy