Discriminated Unions in TypeScript

dogOrPerson.ts

interface Dog {
  age: number;
  name: string;
  bark: () => void;
  type: "dog";
}

interface Person {
  age: number;
  name: string;
  shout: () => void;
  type: "person";
}

function makeNoise(dogOrPerson: Dog | Person): void {
  switch (dogOrPerson.type) {
    case "dog": {
      dogOrPerson.bark();
      break;
    }
    case "person": {
      dogOrPerson.shout();
      break;
    }
  }
}