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elseIfDuplicates

Reports duplicate conditions in if-else-if chains that make code unreachable.

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

When an if-else-if chain contains duplicate conditions, the branch with the duplicate condition will never execute. This is because the earlier identical condition will always be evaluated first and match when true, preventing the duplicate condition from ever being reached. Duplicate conditions typically indicate a copy-paste error or a logic mistake in the code.

Examples

Section titled “Examples”
AE53 (statuAE=<==sp ansty="le--0:#D6DEEB;--1:#403F">5<3 sp ansty="le--0:#D9F5DD;--1:#1111">1<1"sp ansty="le--0:#ECC48D;--1:#984E">4Dpendi1<1"sp ansty="le--0:#D6DEEB;--1:#403F">53)< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0handlePendi53(<);d ivclassNa="meec-li">53<} sp ansty="le--0:#C792EA;--1:#8844">AEel5<3 sp ansty="le--0:#C792EA;--1:#8844">AE53 (statuAE=<==sp ansty="le--0:#D6DEEB;--1:#403F">5<3 sp ansty="le--0:#D9F5DD;--1:#1111">1<1"sp ansty="le--0:#ECC48D;--1:#984E">4Dacti1<1"sp ansty="le--0:#D6DEEB;--1:#403F">53)< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0handleActi53(<);d ivclassNa="meec-li">53<} sp ansty="le--0:#C792EA;--1:#8844">AEel5<3 sp ansty="le--0:#C792EA;--1:#8844">AE53 (statuAE=<==sp ansty="le--0:#D6DEEB;--1:#403F">5<3 sp ansty="le--0:#D9F5DD;--1:#1111">1<1"sp ansty="le--0:#ECC48D;--1:#984E">4Dpendi1<1"sp ansty="le--0:#D6DEEB;--1:#403F">53)< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0handlePendingAga53(<);d ivclassNa="meec-li">5<3}d ivclassNa="meco"><}d>AE53 (isValiAE<&&sp ansty="le--0:#D6DEEB;--1:#403F">53 isActive)< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0processVal53(<);d ivclassNa="meec-li">53<} sp ansty="le--0:#C792EA;--1:#8844">AEel5<3 sp ansty="le--0:#C792EA;--1:#8844">AE53 (isPending)< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0processPendi53(<);d ivclassNa="meec-li">53<} sp ansty="le--0:#C792EA;--1:#8844">AEel5<3 sp ansty="le--0:#C792EA;--1:#8844">AE53 (isValiAE<&&sp ansty="le--0:#D6DEEB;--1:#403F">53 isActive)< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0processValidAga53(<);d ivclassNa="meec-li">5<3}d ivclassNa="meco"><}d>AE53 (counAE=<==sp ansty="le--0:#D6DEEB;--1:#403F">5<3 sp ansty="le--0:#F78C6C;--1:#AA09">8<21sp ansty="le--0:#D6DEEB;--1:#403F">53)< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0handleO53(<);d ivclassNa="meec-li">53<} sp ansty="le--0:#C792EA;--1:#8844">AEel5<3 sp ansty="le--0:#C792EA;--1:#8844">AE53 (counAE=<==sp ansty="le--0:#D6DEEB;--1:#403F">5<3 sp ansty="le--0:#F78C6C;--1:#AA09">8<22sp ansty="le--0:#D6DEEB;--1:#403F">53)< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0handleT53(<);d ivclassNa="meec-li">53<} sp ansty="le--0:#C792EA;--1:#8844">AEel5<3 sp ansty="le--0:#C792EA;--1:#8844">AE53 (counAE=<==sp ansty="le--0:#D6DEEB;--1:#403F">5<3 sp ansty="le--0:#F78C6C;--1:#AA09">8<21sp ansty="le--0:#D6DEEB;--1:#403F">53)< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0handleOneAga53(<);d ivclassNa="meec-li">5<3}d ivclassNa="meco"><}d>
443F53 (sta44A31<111" spans="tyle--0:#ECC48D;--1:#98">4E4Dpen1<111" spans="tyle--0:#D6DEEB;--1:#40">3F5<3) {divclass="Nameec-">de61B0handlePen3F5<3() ;divclass="Nameec-">3F<53} spans="tyle--0:#C792EA;--1:#88">44AE3443F53 (sta44A31<111" spans="tyle--0:#ECC48D;--1:#98">4E4Dac1<111" spans="tyle--0:#D6DEEB;--1:#40">3F5<3) {divclass="Nameec-">de61B0handleAc3F5<3() ;divclass="Nameec-">3F<53} spans="tyle--0:#C792EA;--1:#88">44AE3443F53 (sta44A31<111" spans="tyle--0:#ECC48D;--1:#98">4E4Dcompl1<111" spans="tyle--0:#D6DEEB;--1:#40">3F5<3) {divclass="Nameec-">de61B0handleCompl3F5<3() ;divclass="Nameec-">3<);><}di vdivclass="Nameexpressive-">443F53 (isVa443F53 isActivde61B0processV3F5<3() ;divclass="Nameec-">3F<53} spans="tyle--0:#C792EA;--1:#88">44AE3443F53 (isPendinde61B0processPen3F5<3() ;divclass="Nameec-">3F<53} spans="tyle--0:#C792EA;--1:#88">44AE3443F53 (isVa4434<4AE! spans="tyle--0:#D6DEEB;--1:#40">3F53isActivde61B0processInac3F5<3() ;divclass="Nameec-">3<);><}di vdivclass="Nameexpressive-">443F53 (co44A30<9821 spans="tyle--0:#D6DEEB;--1:#40">3F5<3) {divclass="Nameec-">de61B0handl3F5<3() ;divclass="Nameec-">3F<53} spans="tyle--0:#C792EA;--1:#88">44AE3443F53 (co44A30<9822 spans="tyle--0:#D6DEEB;--1:#40">3F5<3) {divclass="Nameec-">de61B0handl3F5<3() ;divclass="Nameec-">3F<53} spans="tyle--0:#C792EA;--1:#88">44AE3443F53 (co44A30<9823 spans="tyle--0:#D6DEEB;--1:#40">3F5<3) {divclass="Nameec-">de61B0handleT3F5<3() ;divclass="Nameec-">3<);>

Options

Section titled “Options”

This rule is not configurable.

When Not To Use It

Section titled “When Not To Use It”

If your project intentionally uses patterns that look like duplicate conditions but actually modify state behind-the-scenes, you might not want to enable this rule. For example, projects that modify state in computed object get() properties or use Proxy are often considered overly difficult to reason about for both humans and lint rules.

Further Reading

Section titled “Further Reading”

Equivalents in Other Linters

Section titled “Equivalents in Other Linters”