type A = {
    propA: number;
    propB: number;
    propC: number;
    propD: number;
}

type B = {
    propA: number;
    propB: string;
    propC: undefined;
}

type C = A | B;

let test: C;

type TPropA = typeof test.propA; // -> type TPropA = number;
type TPropB = typeof test.propB; // -> type TPropB = string | number;
type TPropC = typeof test.propC; // -> type TPropC = number | undefined;

// TS2551: Property 'propD' does not exist on type 'C'.
type TPropD = typeof test.propD; // -> expected: type TPropD = number | undefined;