regexUnnecessaryNestedQuantifiers

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

✅ This rule is included in the ts logical presets.

When a non-capturing group contains a single quantified element and the group itself is quantified, the nested quantifiers can often be combined into a single quantifier. This rule reports trivially nested quantifiers in regular expressions that can be simplified.

Examples

Optional in One-or-More

(?:a?)+ can be simplified to a* because an optional element repeated one or more times is equivalent to zero or more.

❌ Incorrect

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

✅ Correct

const pattern = /a*/;

One-or-More in One-or-More

(?:a+)+ can be simplified to a+ because one or more of one or more is still one or more.

❌ Incorrect

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

✅ Correct

const pattern = /a+/;

One-or-More in Zero-or-More

(?:a+)* can be simplified to a* because one or more repeated zero or more times is zero or more.

❌ Incorrect

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

✅ Correct

const pattern = /a*/;

Character Classes

The rule also works with character classes and escape sequences.

❌ Incorrect

const pattern = /(?:[a-z]?)+/;
const digits = /(?:\d+)+/;

✅ Correct

const pattern = /[a-z]*/;
const digits = /\d+/;

RegExp Constructor

❌ Incorrect

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

✅ Correct

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

Options

This rule is not configurable.

When Not To Use It

If you prefer to keep the nested structure for readability or documentation purposes, or if you need the specific behavior of the non-capturing group for replacement operations, you might prefer to disable this rule. You might consider using Flint disable comments and/or configuration file disables for those specific situations instead of completely disabling this rule.

Further Reading

• MDN: Quantifiers
• MDN: Non-capturing group

Equivalents in Other Linters

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