tests/cases/conformance/types/namedTypes/classWithOptionalParameter.ts(4,6): error TS1112: A class member cannot be declared optional. tests/cases/conformance/types/namedTypes/classWithOptionalParameter.ts(5,6): error TS1112: A class member cannot be declared optional. tests/cases/conformance/types/namedTypes/classWithOptionalParameter.ts(9,6): error TS1112: A class member cannot be declared optional. tests/cases/conformance/types/namedTypes/classWithOptionalParameter.ts(10,6): error TS1112: A class member cannot be declared optional. ==== tests/cases/conformance/types/namedTypes/classWithOptionalParameter.ts (4 errors) ==== // classes do not permit optional parameters, these are errors class C { x?: string; ~ !!! error TS1112: A class member cannot be declared optional. f?() {} ~ !!! error TS1112: A class member cannot be declared optional. } class C2 { x?: T; ~ !!! error TS1112: A class member cannot be declared optional. f?(x: T) {} ~ !!! error TS1112: A class member cannot be declared optional. }