ES6 Class

class Mammel {
  constructor(legs){
    this.legs = legs;
  }
  eat(){
    console.log('eating...');
  }
  static count(){
    console.log('static count...');
  }
}

class Dog extends Mammel{
  constructor(name, legs){
    super(legs);
    this.name = name;
  }
  sleep(){
    super.eat();
    console.log('sleeping');
  }
}

let d = new Dog('fido', 4);
d.sleep();
d.eat();
console.log('d', d);