Callbacks, Promises and Async/Await

async.js

// The Problem
function fn(val) {
  setTimeout(function() {
    console.log(val)
  }, val)
}

function executeAll() {
  fn(20)
  fn(20)
  fn(400)
  fn(20)
}

executeAll()



// The Solution (through callback)
function fn(val, callback) {
  setTimeout(function() {
    console.log(val)
    callback()
  }, val)
}

function executeAll() {
  fn(20, function() {
    fn(20, function() {
      fn(400, function() {
        fn(20, function() {

        })
      })
    })
  })
}

executeAll()


// The Solution (through Promise)
function fn(val) {
  return new Promise(function (resolve, reject) {
    setTimeout(function() {
      console.log(val)
      resolve()
    }, val)
  })
  
}

function executeAll() {
  fn(20).then(function() {
    return fn(20)
  }).then(function() {
    return fn(400)
  }).then(function() {
    return fn(20)
  })
}

executeAll()



// The Solution (through Async/Await)
function fn(val) {
  return new Promise(function (resolve, reject) {
    setTimeout(function() {
      console.log(val)
      resolve()
    }, val)
  })
  
}

async function executeAll() {
  await fn(20)
  await fn(20)
  await fn(400)
  await fn(20)
}

executeAll()