Solution to exercise posted @ https://gist.github.com/arol/85fbd96648a5d1b6b28f204932fd3b9b

async-solution.js

const randomNumber = () => {
  return Math.random();
}

// 1. Make it wait for 1 sec. with `setTimeout`
const timeoutRandomNumber = (cb) => {
  setTimeout(() => {
    cb(null, randomNumber())
  }, 1000);
}

// 2. Now wrap the timeout version to work with promises
const promiseRandomNumber = () => {
  return new Promise((resolve, reject) => {
    timeoutRandomNumber((err, rnd) => {
      if (err) reject(err);
      else resolve(rnd);
    })
  });
}

// 3. Finally, code a final version with async await.
const asyncRandomNumber = async () => {
  // Just a clarification, this is quite absurd and we're doing it only for
  // learning purposes. Returning the await of another function in an async
  // function (with no other awaits) it's useless. Simply return the execution
  // of `promiseRandomNumber`, which already returns a promise.
  return await promiseRandomNumber();
}

const rangedRandomNumber = (base, min, max) => {
  return Math.floor((base*(max-min))+min);
}

const main = async () => {
  // 0. Without asynchronicity
  const rnd = randomNumber()
  console.log('Not asynchronous', rangedRandomNumber(rnd, 14, 42));


  // 1. Callbacks
  timeoutRandomNumber((err, rnd) => {
    if(err) {
      // return in here is only for halting
      return console.error(err);
    }
    console.log('Callback', rangedRandomNumber(rnd, 14, 42));
  })

  // 2. Promises
  promiseRandomNumber()
  .then(rnd => {
    console.log('Promise', rangedRandomNumber(rnd, 14, 42));
  })
  .catch(e => {
    console.error(e);
  }) 

  // 4. async/await (wee need to prefix main with async. See line 31)
  const number = await asyncRandomNumber();
  console.log('async/await', rangedRandomNumber(number, 14, 42));
}

main();