prototype-chain-with-class.js

'use strict';
class Animal {
  constructor (voice) {
    this.voice = voice || 'Grunt';
  }
  
  speak() {
    return this.voice;
  }
}

class Cat extends Animal {
  constructor (name, color) {
    super('Meow');
    this.name = name;
    this.color = color;
  }
  
}

var fluffy = new Cat('Fluffy', 'White');
console.log(fluffy.speaK());