regexUnusedFlags

Reports regular expression flags that have no effect on the pattern.

✅ This rule is included in the ts logical presets.

Reports regular expression flags that have no effect on the pattern. Unused flags add unnecessary complexity and may mislead readers about the regex’s behavior.

Examples

Unused i Flag (ignoreCase)

The i flag is useless when the pattern contains no ASCII letters (A-Za-z).

❌ Incorrect

const pattern = /123/i;
const digits = /\d+/i;

✅ Correct

const pattern = /abc/i;
const alphanumeric = /[a-z0-9]+/i;

Unused m Flag (multiline)

The m flag is useless when the pattern contains no ^ or $ anchors.

❌ Incorrect

const pattern = /abc/m;
const whitespace = /\s+/m;

✅ Correct

const pattern = /^abc/m;
const lineEnd = /foo$/m;

Unused s Flag (dotAll)

The s flag is useless when the pattern contains no . metacharacters.

❌ Incorrect

const pattern = /abc/s;
const escaped = /a\.b/s;

✅ Correct

const pattern = /a.b/s;
const multiline = /.*content.*/s;

Multiple Unused Flags

❌ Incorrect

const pattern = /123/ims;

✅ Correct

const pattern = /123/;

Options

This rule is not configurable.

When Not To Use It

If you add flags preemptively to patterns you intend to extend later, you might want to disable this rule.

Further Reading

• MDN: Regular expression flags
• MDN: RegExp

Equivalents in Other Linters

• ESLint: regexp/no-useless-flag