regexUnnecessaryLookaroundAssertions

Reports unnecessary nested lookaround assertions in regular expressions.

✅ This rule is included in the ts logical presets.

Reports unnecessary nested lookaround assertions in regular expressions. A positive lookahead at the end of another lookahead, or a positive lookbehind at the start of another lookbehind, is redundant because the nested assertion can be inlined into the parent.

Examples

Unnecessary Lookahead at End

❌ Incorre

AEconsB0patteAE <= sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8F(?=content(?=nested<))sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">AEconsB0patteAE <= sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8F(?<=(?<=nested)conten1<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meco">AEconsB0patteAE <= sp ansty="le--0:#D9F5DD;--1:#1111">1<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8F(?!content(?=nested<))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:#5CA7E4;--1:#3A">688F(?=contentNes1<111/ spans="tyle--0:#D6DEEB;--1:#40">3<;di vdivclass="Nameexpressive-">44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">688F(?<=nestedCont1<111/ spans="tyle--0:#D6DEEB;--1:#40">3<;di vdivclass="Nameexpressive-">44AEco61B0pat446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">688F(?!contentNes1<111/ spans="tyle--0:#D6DEEB;--1:#40">3

Options

This rule is not configurable.

When Not To Use It

If you are intentionally structuring patterns with nested lookarounds for clarity or readability, you might prefer to disable this rule.

Further Reading

• MDN: Lookahead assertion
• MDN: Lookbehind assertion

Equivalents in Other Linters

• ESLint: regexp/no-extra-lookaround-assertions