regexCharacterClassSetOperations

Reports lookarounds that can be replaced with character class set operations.

✅ This rule is included in the ts stylistic and stylisticStrict presets.

Regular expressions with the v flag have access to character class set operations like intersection (&&) and subtraction (--). These are more readable and performant than using lookarounds to achieve the same effect.

Examples

❌ Incorre

76// Negative lookahead can be subtractiAEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8F(B0<\dsp ansty="le--0:#5CA7E4;--1:#3A68">8B0<\wsp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">85<3;d ivclassNa="meco">76// Positive lookbehind can be intersectiAEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#82AAFF;--1:#3B61">B0<\wsp ansty="le--0:#5CA7E4;--1:#3A68">8F(?<<=sp ansty="le--0:#82AAFF;--1:#3B61">B0<\dsp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">85<3;d ivclassNa="meco">76// Positive lookahead can be intersectiAEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8F(B0<\dsp ansty="le--0:#5CA7E4;--1:#3A68">8B0<\wsp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">85<3;d ivclassNa="meco">

6376// Use subtraction instead of negative looka44AEco61B0pat446<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\w spans="tyle--0:#82AAFF;--1:#3B">61B0-<-\d] spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fv spans="tyle--0:#D6DEEB;--1:#40">3<]/v><;di vdivclass="Nameexpressive-">6376// Use intersection instead of positive lookbe44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[\w&<&\d] spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fv spans="tyle--0:#D6DEEB;--1:#40">3<]/v><;di vdivclass="Nameexpressive-">6376// Use intersection instead of positive looka44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#82AAFF;--1:#3B">61B0[\w&<&\d] spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fv spans="tyle--0:#D6DEEB;--1:#40">3<]/v><;di vdivclass="Nameexpressive-">6376// Lookarounds without the v flag are v44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">688616<88F) spans="tyle--0:#82AAFF;--1:#3B">611<111/ spans="tyle--0:#D6DEEB;--1:#40">3<\w/><;di vdivclass="Nameexpressive-">6376// Complex lookarounds cannot be conve44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">688F(?!611<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fv spans="tyle--0:#D6DEEB;--1:#40">3

Options

This rule is not configurable.

When Not To Use It

If you prefer the explicit semantics of lookarounds over set operations, this rule might not be for you.

Further Reading

• MDN: Unicode character class escape - v-mode character class
• MDN: Lookahead assertion

Equivalents in Other Linters

• ESLint: regexp/prefer-set-operation