Introduction to ES6 promises

Promises aim to solve a lot of the problems that come up when we have a lot of asynchronous code in our application. They make it a lot easier to manage our asynchronous computations—things such as requesting data from a database. Alternatively, in the case of a weather app, things such as fetching data from a URL.

In the app.js file we do a similar thing using callbacks:

const yargs = require('yargs');

const geocode = require('./geocode/geocode');
const weather = require('./weather/weather');

const argv = yargs
  .options({
    a: {
      demand: true,
      alias: 'address',
      describe: 'Address to fetch weather for',
      string: true
    }
  })
  .help()
  .alias('help', 'h')
  .argv;

geocode.geocodeAddress(argv.address, (errorMessage, results) => {
  if (errorMessage) {
    console.log(errorMessage);
  } else {
    console.log(results.address);
    weather.getWeather(results.latitude, results.longitude, (errorMessage, weatherResults) => {
  ...