README.md

RequiredKeys<Type> constructs a union type by picking all required properties of object type Type

interface StudentWithOptionalName {
  homework: string | undefined;
  name?: string;
  score: number;
}

type PropertiesThatStudentAlwaysHave = RequiredKeys<StudentWithOptionalName>;
//   ^? 'homework' | 'score'

TS validates required properties are always specified, otherwise shows an error

const student: StudentWithOptionalName = {
  homework: undefined,
  score: 0,
};

// error: Property 'homework' is missing in type '{ score: number; }' but required in type 'StudentWithOptionalName'
const studentWithoutHomework: StudentWithOptionalName = {
  //  ^^^^^^^^^^^^^^^^^^^^^^
  score: 0,
};

TS Playground – https://tsplay.dev/mq9gdm