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).

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8F1<23sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">85<3;d ivclassNa="meec-li">AEconsB0digiAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0<\dsp ansty="le--0:#7FDBCA;--1:#096E">7<2+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:#5CA7E4;--1:#3A">6881<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fi spans="tyle--0:#D6DEEB;--1:#40">344AEco61B0alphanum446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[a-z<0-9] spans="tyle--0:#7FDBCA;--1:#09">61<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fi spans="tyle--0:#D6DEEB;--1:#40">3<+/i>

Unused m Flag (multiline)

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

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8Fa1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">85<3;d ivclassNa="meec-li">AEconsB0whitespaAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0<\ssp ansty="le--0:#7FDBCA;--1:#096E">7<2+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:#C792EA;--1:#88">4<4AE^ spans="tyle--0:#5CA7E4;--1:#3A">6881<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fm spans="tyle--0:#D6DEEB;--1:#40">344AEco61B0lin446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6884<4AE$ spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fm spans="tyle--0:#D6DEEB;--1:#40">3<$/m>

Unused s Flag (dotAll)

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

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8Fa1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">85<3;d ivclassNa="meec-li">AEconsB0escapAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">882<\.sp ansty="le--0:#5CA7E4;--1:#3A68">81<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:#5CA7E4;--1:#3A">6<88Fa spans="tyle--0:#82AAFF;--1:#3B">6<1B0. spans="tyle--0:#5CA7E4;--1:#3A">6<88Fb spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fs spans="tyle--0:#D6DEEB;--1:#40">344AEco61B0multi446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">6<1B0. spans="tyle--0:#7FDBCA;--1:#09">6688Fcon6<1B0. spans="tyle--0:#7FDBCA;--1:#09">61<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fs spans="tyle--0:#D6DEEB;--1:#40">3<*/s>

Multiple Unused Flags

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8F1<23sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8Fi5<3;d ivclassNa="meco">

44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6881<111/ spans="tyle--0:#D6DEEB;--1:#40">3<23/>

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