Proto mouse!

es6-proto-mouse.js

let animal = {
  animalType: 'animal',
  
  describe () {
    return `An ${this.animalType}, with ${this.furColor} fur, 
      ${this.legs} legs, and a ${this.tail} tail.`;
  }
};

let mouse = Object.assign(Object.create(animal), {
  animalType: 'mouse',
  furColor: 'brown',
  legs: 4,
  tail: 'long, skinny'
});