regexContradictoryAssertions

Reports elements in regular expressions that contradict assertions.

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

Reports elements in regular expressions that contradict assertions like word boundaries (\b). These contradictions indicate dead code or unintended behavior in the regex pattern.

Examples

Quantifier Always Entered

When a word boundary is between two word characters (or two non-word characters), optional quantifiers following it are always entered.

❌ 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">87<2?sp 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">4468<8F-a spans="tyle--0:#D9F5DD;--1:#11">1<111/ spans="tyle--0:#D6DEEB;--1:#40">3<-a/>

Quantifier Cannot Be Entered

When a word boundary assertion forces a transition that conflicts with the quantifier’s element, the quantifier can never match.

❌ 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">87<2*sp 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">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">4Db-1<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">4E41<111" spans="tyle--0:#D6DEEB;--1:#40">3F<53) ;divclass="Name">

Options

This rule is not configurable.

When Not To Use It

If you intentionally use contradictory assertions for documentation purposes or if you’re working with dynamically constructed regex patterns where the contradictions are not actually problematic, you may disable this rule.

Further Reading

• MDN: Assertions
• MDN: Word boundary assertion

Equivalents in Other Linters

• ESLint: regexp/no-contradiction-with-assertion