TN 2

example.ts

function sound(animal: Dog | Cat) {
  if (animal instanceof Dog) {
    // animal은 Dog로 추론됨.
    animal.bark();
    animal.meow(); // error TS2339: Property 'meow' does not exist on type 'Dog'.
    return;
  }
  if (animal instanceof Cat) {
    // animal은 Cat으로 추론됨.
    animal.bark(); // error TS2339: Property 'bark' does not exist on type 'Cat'.
    animal.meow();
    return;
  }

  // animal은 never로 추론됨.
  animal.bark(); // error TS2339: Property 'bark' does not exist on type 'never'.
  animal.meow(); // error TS2339: Property 'meow' does not exist on type 'never'.
}