Typescript - MappedTypes

Mapped types are a feature in TypeScript which allow you to map over a union of types to create a new type

Using the keyof operator with mapped types gives you a smooth API to create object types from other object types

interface Person {
  name: string;
  age: number;
}

type NullablePerson = {
  [P in keyof Person]: Person[P] | null;
};

// It equals
type NullablePerson = {
  name: string | null;
  age: number | null;
};