tests/cases/conformance/types/objectTypeLiteral/methodSignatures/objectTypesWithOptionalProperties.ts(12,6): error TS1112: A class member cannot be declared optional. tests/cases/conformance/types/objectTypeLiteral/methodSignatures/objectTypesWithOptionalProperties.ts(20,6): error TS1112: A class member cannot be declared optional. tests/cases/conformance/types/objectTypeLiteral/methodSignatures/objectTypesWithOptionalProperties.ts(24,6): error TS1162: An object member cannot be declared optional. ==== tests/cases/conformance/types/objectTypeLiteral/methodSignatures/objectTypesWithOptionalProperties.ts (3 errors) ==== // Basic uses of optional properties var a: { x?: number; // ok } interface I { x?: number; // ok } class C { x?: number; // error ~ !!! error TS1112: A class member cannot be declared optional. } interface I2 { x?: T; // ok } class C2 { x?: T; // error ~ !!! error TS1112: A class member cannot be declared optional. } var b = { x?: 1 // error ~ !!! error TS1162: An object member cannot be declared optional. }