Factory Functions for Mixin Composition

factory-function-for-mixin-composition.js

// See https://medium.com/javascript-scene/javascript-factory-functions-with-es6-4d224591a8b1

const pipe = (...fns) => x => fns.reduce((y, f) => f(y), x);

const withConstructor = constructor => o => ({
  // create the delegate [[Prototype]]
  __proto__: {
    // add the constructor prop to the new [[Prototype]]
    constructor
  },
  // mix all o's props into the new object
  ...o
});

const withFlying = o => {
  let isFlying = false;
  return {
    ...o,
    fly () {
      isFlying = true;
      return this;
    },
    land () {
      isFlying = false;
      return this;
    },
    isFlying: () => isFlying
  }
};

const withBattery = ({ capacity }) => o => {
  let percentCharged = 100;
  return {
    ...o,
    draw (percent) {
      const remaining = percentCharged - percent;
      percentCharged = remaining > 0 ? remaining : 0;
      return this;
    },
    getCharge: () => percentCharged,
    getCapacity () {
      return capacity;
    }
  };
};

const createDrone = ({ capacity = '3000mAh' }) => pipe(
  withFlying,
  withBattery({ capacity }),
  withConstructor(createDrone)
)({});

const myDrone = createDrone({ capacity: '5500mAh' });

console.log(`
  can fly:  ${ myDrone.fly().isFlying() === true }
  can land: ${ myDrone.land().isFlying() === false }
  battery capacity: ${ myDrone.getCapacity() }
  battery status: ${ myDrone.draw(50).getCharge() }%
  battery drained: ${ myDrone.draw(75).getCharge() }%
`);

console.log(`
  constructor linked: ${ myDrone.constructor === createDrone }
`);