Using Promises, Async/await to fix callback hell

callback-example.js

function doStep1(init, callback) {
  const result = init + 1
  callback(result)
}

function doStep2(init, callback) {
  const result = init + 2
  callback(result)
}

function doStep3(init, callback) {
  const result = init + 3
  callback(result)
}

function doStep4(init, callback) {
  const result = init + 4
  callback(result)
}

function doOperationCallback() {
  doStep1(0, (result1) => {
    doStep2(result1, (result2) => {
      doStep3(result2, (result3) => {
        doStep4(result3, (total) => {
	      console.log(`Total is: ${total}`)
        })
      });
    });
  });
}

doOperationCallback()

promise-example.js

function doStep1(init) {
  const result = init + 1
  return new Promise((resolve, reject) => {
    resolve(result)
  })
}

function doStep2(init) {
  const result = init + 2
  return new Promise((resolve, reject) => {
    resolve(result)
  })
}

function doStep3(init) {
  const result = init + 3
  return new Promise((resolve, reject) => {
    resolve(result)
  })
}

function doStep4(init) {
  const result = init + 4
  return new Promise((resolve, reject) => {
    resolve(result)
  })
}

function doOperationPromise() {
  return new Promise((resolve, reject) => {
  	resolve(0)
  })
    .then(doStep1)
    .then(doStep2)
    .then(doStep3)
    .then(doStep4)
    .then(total => console.log(`Total is: ${total}`))
}

async function doOperationAsyncAwait() {
  const result1 = await doStep1(0)
  const result2 = await doStep2(result1)
  const result3 = await doStep3(result2)
  const total = await doStep4(result3)
  console.log(`Total is: ${total}`)
}

doOperationPromise()
doOperationAsyncAwait()