demo.ts

type Pet = IDog | ICat | ILizard;

interface IPet {
  type: string;
  name: string;
}

interface IDog extends IPet {
  type: 'dog';
}

interface ICat extends IPet {
  type: 'cat';
}

interface ILizard extends IPet {
  type: 'lizard';
}

function woof(dog: IDog) {
  console.log(`${dog.name} says woof woof`);
}

function meow(cat: ICat) {
  console.log(`${cat.name} says meow`);
}

const yourPets: Pet[] = [{type: 'dog', name: 'frodo'}, {type: 'cat', name: 'garfield'}];
for(const pet of yourPets) {
  if(pet.type === 'dog') {
     woof(pet);
  }else if(pet.type === 'cat') {
     meow(pet);
  }else{
    const n: never = pet; 
  }
}