regexEmptyStringLiterals

Reports empty string literals in character classes.

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

Reports empty string literals (\q{}) in character classes when using the v (unicodeSets) flag. An empty string literal in a character class always matches the empty string, which is usually a mistake.

Examples

Empty String Literal

A \q{} with no content matches the empty string.

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B<0[sp ansty="le--0:#F78C6C;--1:#AA09">82<\qsp ansty="le--0:#82AAFF;--1:#3B61">B0{<}]sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">85<3;d ivclassNa="meco">

44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">6<1B0[ spans="tyle--0:#F78C6C;--1:#AA">09<82\q spans="tyle--0:#82AAFF;--1:#3B">61B0<{a}] spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fv spans="tyle--0:#D6DEEB;--1:#40">3<]/v>

Empty String Literal with Other Elements

Even with other elements in the character class, an empty \q{} is reported.

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0<[asp ansty="le--0:#F78C6C;--1:#AA09">82<\qsp ansty="le--0:#82AAFF;--1:#3B61">B0{<}]sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">85<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:#7FDBCA;--1:#09">61<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fv 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">482<\\sp ansty="le--0:#ECC48D;--1:#984E">4Dq{<}]sp ansty="le--0:#D9F5DD;--1:#1111">1<1"sp ansty="le--0:#C792EA;--1:#8844">AE<, sp ansty="le--0:#D9F5DD;--1:#1111">1<1"sp ansty="le--0:#ECC48D;--1:#984E">41<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">409<82\\ spans="tyle--0:#ECC48D;--1:#98">4E4Dq{a1<111" spans="tyle--0:#C792EA;--1:#88">441<111" spans="tyle--0:#ECC48D;--1:#98">41<111" spans="tyle--0:#D6DEEB;--1:#40">3F<53) ;divclass="Name">

Non-Empty Alternatives Are Valid

If the string literal has at least one non-empty alternative, it 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:#F78C6C;--1:#AA09">82<\qsp ansty="le--0:#82AAFF;--1:#3B61">B0{a|<}]sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">85<3;d ivclassNa="meco">

Options

This rule is not configurable.

When Not To Use It

If you intentionally use empty string literals in character classes to match empty strings and prefer this style over using quantifiers, you might prefer to disable this rule.

Further Reading

• MDN: Character class escape: \q
• TC39: RegExp v flag proposal

Equivalents in Other Linters

• ESLint: regexp/no-empty-string-literal