👨🏻‍🚒Asynchronous JavaScript(2) - Callback

const printString = string => {
  setTimeout(() => {
    console.log(string)
  }, Math.floor(Math.random() * 100) + 1)
}

const printAll = () => {
  printString('A')
  printString('B')
  printString('C')
}
printAll() // what do you expect?

const printString = (string, callback) => {
  setTimeout(() => {
    console.log(string)
    callback()
  }, Math.floor(Math.random() * 100) + 1)
}

const printAll = () => {
  printString('A', () => {
    printString('B', () => {
      printString('C', () => {})
    })
  })
}
printAll() // now what do you expect?

// Callback error handling Design
const somethingGonnaHappen = callback => {
  waitingUntilSomethingHappens()

  if (isSomethingGood) {
    callback(null, data)
  }

  if (isSomethingBad) {
    callback(error, null)
  }
}

// Usage
somethingGonnaHappen((err, data) => {
  if (err) {
    console.log('ERR!!')
    return
  }
  return data
})