regexEmptyCharacterClasses

Reports character classes that match no characters.

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

Reports empty character classes in regular expressions. An empty character class [] matches nothing and always fails, which is usually a mistake.

Examples

Empty Character Class

An empty character class matches nothing.

❌ Incorrect

const pattern = /[]/;

✅ Correct

const pattern = /[a]/;

Empty Class in Pattern

An empty character class in a larger pattern causes the entire match to fail.

❌ Incorrect

const pattern = /a[]b/;

✅ Correct

const pattern = /ab/;

RegExp Constructor

The rule also checks regex patterns in RegExp constructor calls.

❌ Incorrect

const pattern = new RegExp("[]");

✅ Correct

const pattern = new RegExp("[a-z]");

Negated Empty Class Is Valid

A negated empty character class [^] matches any character and is valid.

✅ Correct

const pattern = /[^]/;

Options

This rule is not configurable.

When Not To Use It

If you intentionally use empty character classes as a way to create a pattern that never matches (e.g., for testing purposes), you might prefer to disable this rule.

Further Reading

• MDN: Character classes
• ECMAScript specification: CharacterClass

Equivalents in Other Linters

• Biome: noEmptyCharacterClassInRegex
• Deno: no-empty-character-class
• ESLint: regexp/no-empty-character-classno-empty-character-class
• Oxlint: eslint/no-empty-character-class