interface Dog {
  run: Function
}
interface Bird {
  fly: Function
}
function myFunction(animal: Dog | Bird) {
  if (animal.fly) {
    animal.fly();
  } else {
  animal.run();
  }
}
const dog: Dog = {
  run: function () {
    alert("Let's run dogs");
  }
};
const bird: Bird = {
  fly: function () {
    alert("Let's fly birds");
  }
};
myFunction(dog); // prints Let's run dogs
myFunction(bird); // prints Let's fly birds