function Animal(name, energy) {
    let obj = Object.create(Animal.prototype);
    obj.name = name;
    obj.energy = energy;
    return obj;
}

Animal.prototype.eat = function (amount) {
    console.log(`${this.name} is eating.`);
    this.energy += amount;
}

Animal.prototype.sleep = function (length) {
    console.log(`${this.name} is sleeping.`);
    this.energy += length;
}

Animal.prototype.play = function (length) {
    console.log(`${this.name} is playing.`);
    this.energy -= length;
}

const leo = Animal("Leo", 7);
leo.sleep(8);
leo.eat(2);
leo.play(10);

const bob = Animal("Bob", 3);
bob.sleep(8);
bob.eat(2);
bob.play(10);