Inheritance: extends, super and instanceof

class Animal {
  constructor(name) {
    this.name = name;
  }

  speak() {
    return `${this.name} makes a sound`;
  }
}

class Dog extends Animal {
  speak() {
    return `${this.name} barks`;     // overrides the parent method
  }
}

const generic = new Animal("Creature");
const rex = new Dog("Rex");

console.log(generic.speak()); // → Creature makes a sound
console.log(rex.speak());     // → Rex barks

class Animal {
  constructor(name) { this.name = name; }
}

class Dog extends Animal {
  constructor(name, breed) {
    super(name);              // run the parent constructor
    this.breed = breed;       // then add your own data
  }
}

console.log(new Dog("Rex", "Collie")); // → Dog { name: Rex, breed: Collie }

class Animal {
  speak() { return "makes a sound"; }
}

class Dog extends Animal {
  speak() {
    return `barks and ${super.speak()}`;
  }
}

console.log(new Dog().speak()); // → barks and makes a sound

class Animal {}
class Dog extends Animal {}
const rex = new Dog();

console.log(rex instanceof Dog);     // → true
console.log(rex instanceof Animal);  // → true  (a Dog is an Animal)
console.log(rex instanceof Object);  // → true
console.log(new Animal() instanceof Dog); // → false

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = "ValidationError";
  }
}

console.log(new ValidationError("bad input") instanceof Error); // → true