Black box composition example

black-box-composition.js

const pooper = (delay) => {
  return {
    lastPoop: null,
    getPoopDelay () { return delay; },
    canPoop: function(now) {
        return this.lastPoop ? (this.lastPoop + delay) >= now : true
    },
    poop: function(){
        if(this.canPoop(new Date())){
            //implementation for pooping is omitted
            this.lastPoop = new Date();
        }
    }
  }
};
const eater = (delay) => {
  return {
    lastMeal: null,
    getEatDelay () { return delay; },
    canEat: function(now) {
        return this.lastMeal ? (this.lastMeal + delay) >= now : true
    },
    eat: function(food){
        if(this.canEat(new Date())){
            //implementation for eating is omitted
            this.lastMeal = new Date();
        }
    }
  };
};

const dog = (poopDelay, eatDelay, pooper, eater) => Object.assign({}, pooper(poopDelay), eater(eatDelay));
let myDog = dog(4, 8, pooper, eater);
console.log(myDog.getPoopDelay()) //4
console.log(myDog.getEatDelay()) //8

Hi, does this.delay need tidying up?

Yes. Done.