Decoration with mixins in ES6

decorators.js

// The object to be decorated
class Coffee {
  price() {
    return 10;
  }

  notify(message) {
    console.log('coffee got a message: ' + message);
  }
}

// Another object
class WithCream {
  price() {
    return 5;
  }

  notify(message) {
    console.log('withcream got a message: ' + message);
  }
}

// The way the decoration is done
const CoffeeDecorator = {
  decorate(original) {
    const decorated = Object.create(original);
    decorated.price = () => {
      return this.price() + original.price();
    }
    decorated.notify = (message) => {
      this.notify(message); 
      original.notify(message);
    }
    return decorated;
  }
}

// The granting of the decorator role
Object.assign(WithCream.prototype, CoffeeDecorator);

// An object that will play a role
class Barista {
  closeShop() {
    this.notifySubscribers('Shop is shutting');
  }
}

// The way observing is done
const Observable = {
  subscribers() {
    return this._subscribers || (this._subscribers = []);
  },
  addSubscriber(subscriber) {
    return this.subscribers().push(subscriber);
  },
  notifySubscribers(event){
    return this.subscribers().map((s) => s.notify(event));
  }
};

// The granting of the Observer role
Object.assign(Barista.prototype, Observable);

// do some decorating
const original = new Coffee;
const dec = new WithCream;
const decorated = dec.decorate(original);

// see the prices are added per specified decorator logic
console.log(original.price());
console.log(decorated.price());

// make an observable and observe it
const barista = new Barista;
barista.addSubscriber(decorated);

// see that each thing is notified per specified notification logic
barista.closeShop();

// dynamically add a property
// no inheritance!
Object.assign(Coffee.prototype, Observable);

const customer = {
  notify(event) {
    console.log('Customer got a message: ' + event);
  }
}

const noisyCoffee = new Coffee;
noisyCoffee.addSubscriber(customer);
noisyCoffee.notifySubscribers('Caution HOT!')