House class with rooms

house.ts

/**
 * This code would live inside the library.
 */

class House {
  // Private
  #rooms: Array<Room> = [];

  getRooms(): Array<Room> {
    return this.#rooms;
  }

  addRoom(room: Room): void {
    this.#rooms.push(room);
  }
}

interface Room {
  // Anything that extends this interface HAS to have
  // a name prop now.
  name: string;
}

/**
 * This code would live in userland (aka how you'd use the library).
 */

// Now anywhere that accepts type Room, you can also use Bathroom,
// because it's base type is Room. (like in `House.addRoom(room)`)
interface Bathroom extends Room {
  full: boolean;
  // etc...
}

interface Bedroom extends Room {
  sqFt: number;
  // etc...
}

const myHouse = new House();

const masterBath: Bathroom = {
  name: 'master bath',
  full: true,
};

const guestBedroom: Bedroom = {
  name: 'downstairs guest',
  sqFt: 300,
};

[masterBath, guestBedroom].forEach((roomToAdd) => {
  // If `roomToAdd` does not satisfy the Room interface
  // this would throw an error (red squiggly lines).
  myHouse.addRoom(roomToAdd));
};
                                   
console.log( myHouse.getRooms() );