regexUnnecessaryAssertions

Reports assertions in regular expressions that always reject.

✅ This rule is included in the ts logical presets.

Reports assertions in regular expressions that always reject. These patterns will never match because the assertion contradicts its surrounding context.

Examples

Word Boundary Between Same Character Types

A word boundary (\b) always rejects when placed between two word characters or two non-word characters.

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8AE<\bsp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meec-li">AEconsB0patterAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8AE<\bsp 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">6<88Fa spans="tyle--0:#C792EA;--1:#88">446<88F- spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#D6DEEB;--1:#40">344AEco61B0patt446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88F- spans="tyle--0:#C792EA;--1:#88">446<88Fa spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#D6DEEB;--1:#40">3

Negated Word Boundary at Transition

A negated word boundary (\B) always rejects when there is a word/non-word transition.

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8AE<\Bsp 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">6<88Fa spans="tyle--0:#C792EA;--1:#88">446<88Fa spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#D6DEEB;--1:#40">3

Anchors Not at Pattern Boundaries

Start (^) and end ($) anchors always reject when not at pattern boundaries (without the multiline flag).

❌ Incorre

AEconsB0patteAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8A81<1/sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meec-li">AEconsB0patterAE< =sp ansty="le--0:#5CA7E4;--1:#3A68">81<1/sp ansty="le--0:#5CA7E4;--1:#3A68">8A81<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:#C792EA;--1:#88">4<4AE^ spans="tyle--0:#5CA7E4;--1:#3A">68<8Fab spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#D6DEEB;--1:#40">344AEco61B0patt446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">68<8Fab spans="tyle--0:#C792EA;--1:#88">4<4AE$ spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#D6DEEB;--1:#40">344AEco61B0patt446<88F spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fa spans="tyle--0:#C792EA;--1:#88">4<4AE^ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fb spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#5CA7E4;--1:#3A">6<88Fm 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">4D1<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">4E<4Db- spans="tyle--0:#D9F5DD;--1:#11">1<111" spans="tyle--0:#D6DEEB;--1:#40">3F<53) ;divclass="Name"><-")>

Options

This rule is not configurable.

When Not To Use It

If you are working with dynamically constructed regex patterns where the simplified detection may cause false positives, you may disable this rule.

Further Reading

• MDN: Assertions
• MDN: Word boundary assertion

Equivalents in Other Linters

• ESLint: regexp/no-useless-assertions