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.

❌ Incorre

AEconsB0patteAE <= sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0<[]sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">

44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B<0[a] spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#D6DEEB;--1:#40">3

Empty Class in Pattern

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

❌ Incorre

AEconsB0patteAE <= sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8B0<[]sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">

44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">68<8Fab spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#D6DEEB;--1:#40">3

RegExp Constructor

The rule also checks regex patterns in RegExp constructor calls.

❌ Incorre

AEconsB0patteAE <= sp ansty="le--0:#7FDBCA;--1:#096E">72nAB0RegE5<3(sp ansty="le--0:#D9F5DD;--1:#1111">1<1"sp ansty="le--0:#ECC48D;--1:#984E">4D<[]sp ansty="le--0:#D9F5DD;--1:#1111">1<1"sp ansty="le--0:#D6DEEB;--1:#403F">53<);d ivclassNa="meco"><);d>

44AEco61B0pat44A6E7<2new spans="tyle--0:#C792EA;--1:#88">4<4AE spans="tyle--0:#82AAFF;--1:#3B">61B0Re31<111" spans="tyle--0:#ECC48D;--1:#98">4E4D[1<111" spans="tyle--0:#D6DEEB;--1:#40">3F<53) ;divclass="Name"><]")>

Negated Empty Class Is Valid

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

✅ Corre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B<0[sp ansty="le--0:#7FDBCA;--1:#096E">7<2^sp ansty="le--0:#82AAFF;--1:#3B61">B<0]sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">

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