classMemberDuplicates

Reports duplicate class member names that will be overwritten.

✅ This rule is included in the ts javascript presets.

Duplicate class members are legal in JavaScript, but only the last definition is used. This can lead to confusion and bugs, especially when maintaining the code.

Examples

❌ Incorre

AEcla5<3 sp ansty="le--0:#FFCB8B;--1:#1111">11F53< {d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0b11<()sp ansty="le--0:#D6DEEB;--1:#403F">53 <{}d ivclassNa="meec-li">nt< sp ansty="le--0:#82AAFF;--1:#3B61">B0b11<()sp ansty="le--0:#D6DEEB;--1:#403F">53 <{}d ivclassNa="meec-li">5<3}d ivclassNa="meco"><}d>AEcla5<3 sp ansty="le--0:#FFCB8B;--1:#1111">11F53< {d ivclassNa="meec-li">nt< sp ansty="le--0:#C792EA;--1:#8844">AEg5<3 sp ansty="le--0:#82AAFF;--1:#3B61">B0b11<()sp ansty="le--0:#D6DEEB;--1:#403F">53< {d ivclassNa="meec-li">nt < sp ansty="le--0:#C792EA;--1:#8844">AEretu5<3 sp ansty="le--0:#F78C6C;--1:#AA09">8<21sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meec-li">53< sp ansty="le--0:#D6DEEB;--1:#403F">5<3}d ivclassNa="meec-li">nt< sp ansty="le--0:#C792EA;--1:#8844">AEg5<3 sp ansty="le--0:#82AAFF;--1:#3B61">B0b11<()sp ansty="le--0:#D6DEEB;--1:#403F">53< {d ivclassNa="meec-li">nt < sp ansty="le--0:#C792EA;--1:#8844">AEretu5<3 sp ansty="le--0:#F78C6C;--1:#AA09">8<22sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meec-li">53< sp ansty="le--0:#D6DEEB;--1:#403F">5<3}d ivclassNa="meec-li">5<3}d ivclassNa="meco"><}d>AEcla5<3 sp ansty="le--0:#FFCB8B;--1:#1111">11F53< {d ivclassNa="meec-li">53< sp ansty="le--0:#D6DEEB;--1:#403F">53baA5<3 sp ansty="le--0:#F78C6C;--1:#AA09">8<21sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meec-li">53< sp ansty="le--0:#D6DEEB;--1:#403F">53baA5<3 sp ansty="le--0:#F78C6C;--1:#AA09">8<22sp ansty="le--0:#D6DEEB;--1:#403F">5<3;d ivclassNa="meec-li">5<3}d ivclassNa="meco"><}d>

44AEc3111<1Foo spans="tyle--0:#D6DEEB;--1:#40">3F<53 {divclass="Nameec-">de61B<0bar spans="tyle--0:#D9F5DD;--1:#11">11<11() spans="tyle--0:#D6DEEB;--1:#40">3F5<3 { }divclass="Nameec-">de61B<0baz spans="tyle--0:#D9F5DD;--1:#11">11<11() spans="tyle--0:#D6DEEB;--1:#40">3F5<3 { }divclass="Nameec-">3<{}><}di vdivclass="Nameexpressive-">44AEc3111<1Foo spans="tyle--0:#D6DEEB;--1:#40">3F<53 {divclass="Nameec-">de44A361B<0bar spans="tyle--0:#D9F5DD;--1:#11">11<11() spans="tyle--0:#D6DEEB;--1:#40">3F<53 {divclass="Nameec-">dent< spans="tyle--0:#C792EA;--1:#88">44AEre30<9821 spans="tyle--0:#D6DEEB;--1:#40">33F<53 spans="tyle--0:#D6DEEB;--1:#40">3de44A361B<0bar spans="tyle--0:#D9F5DD;--1:#11">1<111( spans="tyle--0:#D7DBE0;--1:#40">3F53v1<111) spans="tyle--0:#D6DEEB;--1:#40">3F5<3 { }divclass="Nameec-">3<{}><}di vdivclass="Nameexpressive-">44AEc3111<1Foo spans="tyle--0:#D6DEEB;--1:#40">3F<53 {divclass="Nameec-">de61B<0bar spans="tyle--0:#D9F5DD;--1:#11">11<11() spans="tyle--0:#D6DEEB;--1:#40">3F5<3 { }divclass="Nameec-">de44AEst361B<0bar spans="tyle--0:#D9F5DD;--1:#11">11<11() spans="tyle--0:#D6DEEB;--1:#40">3F5<3 { }divclass="Nameec-">3<{}>

Options

This rule is not configurable.

When Not To Use It

This rule should generally always be enabled. There is no valid use case for duplicate class member names.

Further Reading

• MDN documentation on classes

Equivalents in Other Linters

• Biome: noDuplicateClassMembers
• Deno: no-dupe-class-members
• ESLint: no-dupe-class-members@typescript-eslint/no-dupe-class-members
• Oxlint: eslint/no-dupe-class-members