animal.js

class Animal {
  describe () {
    return `An ${this.animalType} with ${this.furColor} fur, 
      ${this.legs} legs, and a ${this.tail} tail.`
  }
  static mouse () {
    return Object.assign(new Animal, {
      animalType: 'mouse',
      furColor: 'brown',
      legs: 4,
      tail: 'long, skinny',
    })
  }
}

Object.assign(Animal.prototype, {
  animalType: 'animal',
})

let mickey = Animal.mouse()