Chained APIs with Asynchronous Functions

async_chained_api.js

// Given
class Solar {
  getBaseMap(callback) {
    setTimeout(function() {
      callback();
      console.log('Getting Base Map');
    }, 600);
  }
  drawRoofOutline(callback) {
    setTimeout(function() {
      callback();
      console.log('User Outlining Roof');
    }, 1000);
  }
  generate3Dmodel(callback) {
    setTimeout(function() {
      callback();
      console.log('Generating 3D model');
    }, 750);
  }
  calculateIrradiance(callback) {
    setTimeout(function() {
      callback();
      console.log('Calculating Irradiance');
    }, 2000);
  }
  placeSolarPanels(callback) {
    setTimeout(function() {
      callback();
      console.log('Placing Solar Panels');
    }, 500);
  }
  simulatePowerSavings(callback) {
    setTimeout(function() {
      callback();
      console.log('Simulating Power Savings');
    }, 3000);
  }
}

// http://blog.minimum.se/2017/07/18/fluent-chained-api-asynchronous-functions-async-methods-Javascript.html
// https://stackoverflow.com/questions/49766184/how-to-chain-async-methods

const slr = new Solar();

const resolve = (prevAction, fn, cb) => {
  return prevAction
    .then(() => new Promise(resolve => fn(resolve)))
    .then(res => cb ? cb(res) : res);
};

const Api = (prevAction = Promise.resolve()) => ({
  getBaseMap: (cb) => Api(
    resolve(prevAction, slr.getBaseMap, cb)
  ),

  drawRoofOutline: (cb) => Api(
    resolve(prevAction, slr.drawRoofOutline, cb)
  ),

  generate3Dmodel: (cb) => Api(
    resolve(prevAction, slr.generate3Dmodel, cb)
  ),

  calculateIrradiance: (cb) => Api(
    resolve(prevAction, slr.calculateIrradiance, cb)
  ),

  placeSolarPanels: (cb) => Api(
    resolve(prevAction, slr.placeSolarPanels, cb)
  ),

  simulatePowerSavings: (cb) => Api(
    resolve(prevAction, slr.simulatePowerSavings, cb)
  ),
});

solar = Api();

solar
  .getBaseMap()
  .drawRoofOutline()
  .generate3Dmodel()
  .calculateIrradiance()
  .placeSolarPanels()
  .simulatePowerSavings();