regexQuestionQuantifiers

Reports quantifiers {0,1} in regular expressions that should use ? instead.

✅ This rule is included in the ts stylisticStrict presets.

Reports quantifiers using {0,1} in regular expressions and suggests using the more concise ? quantifier instead. Both forms are semantically equivalent (matching zero or one of the preceding element), but ? is the idiomatic form.

This rule also reports non-capturing groups with trailing empty alternatives like (?:abc|) and suggests using (?:abc)? instead.

Examples

Greedy Quantifier

❌ Incorrect

const pattern = /a{0,1}/;

✅ Correct

const pattern = /a?/;

Lazy Quantifier

❌ Incorrect

const pattern = /a{0,1}?/;

✅ Correct

const pattern = /a??/;

Groups

❌ Incorrect

const pattern = /(ab){0,1}/;

✅ Correct

const pattern = /(ab)?/;

Trailing Empty Alternative

❌ Incorrect

const pattern = /(?:abc|)/;

✅ Correct

const pattern = /(?:abc)?/;

RegExp Constructor

❌ Incorrect

const pattern = new RegExp("a{0,1}");

✅ Correct

const pattern = new RegExp("a?");

Options

This rule is not configurable.

When Not To Use It

If your project has a style guide that prefers the explicit {0,1} syntax for clarity, or if you are programmatically generating regular expressions where {0,1} is easier to produce, you might want to disable this rule.

Further Reading

• MDN: Quantifier
• MDN: Regular expressions

Equivalents in Other Linters

• ESLint: regexp/prefer-question-quantifier