Extending Functionality

Classes can inherit from each other using the extends keyword.

class Animal {
  constructor(name) { this.name = name; }
  eat() { console.log(this.name + ' is eating.'); }
  toString() { return `Animal: ${this.name}`; }
}

class Rabbit extends Animal {
  hide() { console.log(this.name + ' hides!'); }
}

let rabbit = new Rabbit('White Rabbit');
rabbit.eat();  // Inherited from Animal
rabbit.hide(); // Rabbit's own method

Overriding Methods with super

class Dog extends Animal {
  constructor(name, breed) {
    super(name);  // MUST call super() before using this
    this.breed = breed;
  }

  eat() {
    super.eat(); // Call the parent's eat() first
    console.log('...and wags tail!');
  }
}

let dog = new Dog('Rex', 'Labrador');
dog.eat();
// "Rex is eating."
// "...and wags tail!"