regexDuplicateCharacterClassCharacters

Reports duplicate characters in regular expression character classes.

✅ This rule is included in the ts logical and logicalStrict presets.

Disallows duplicate characters in regular expression character classes. When a character appears multiple times in a character class, only one occurrence is needed. Duplicates are often typing mistakes and can be safely removed.

Examples

Duplicate Characters

❌ Incorrect

const pattern = /[aaa]/;

✅ Correct

const pattern = /[a]/;

Character Already in Range

❌ Incorrect

const pattern = /[a-z a]/;

✅ Correct

const pattern = /[a-z]/;

Duplicate Ranges

❌ Incorrect

const pattern = /[a-z a-z]/;

✅ Correct

const pattern = /[a-z]/;

Options

This rule is not configurable.

When Not To Use It

If you are intentionally using duplicate characters for documentation purposes or have auto-generated patterns, you might prefer to disable this rule.

Further Reading

• MDN: Character class
• MDN: Regular expressions

Equivalents in Other Linters

• ESLint: regexp/no-dupe-characters-character-class