비동기 함수의 순서를 제어하는 방법 3. async & await

//Producer
function gotoCodestates(){
  return new Promise ((resolve, reject) => {
   setTimeout(() => {resolve('1. go to codestates')}, 100)
   })
}

function sitAndCode(){
  return new Promise ((resolve, reject) => {
   setTimeout(() => {resolve('2. sit and code')}, 100)
   })
}

function eatLunch(){
  return new Promise ((resolve, reject) => {
   setTimeout(() => {resolve('3. eat lunch')}, 100)
   })
}

function goToBed(){
  return new Promise ((resolve, reject) => {
   setTimeout(() => {resolve('4. goToBed')}, 100)
   })
}

//Consumer - Promise Chaining
gotoCodestates()
.then(data => {
  console.log(data) //'1. go to codestates'
  return sitAndCode() //꼭 'return'을 해야한다!! 
  //return값으로 promise객체 전달
 })
.then(data => {
  console.log(data) //'2. sit and code'
  return eatLunch() // return값으로 promise객체 전달
 })
.then(data => {
  console.log(data) //'3. eat lunch'
  return goToBed() // return값으로 promise객체 전달
})
.then(data => {
  console.log(data) //'4. goToBed'
})


//Consumer - async & await
const result = async () => {
   const one = await gotoCodestates() //resolve값
   console.log(one) // '1. go to codestates'

   const two = await sitAndCode()
   console.log(two) // '2. sit and code'
   
   const three = await eatLunch()
   console.log(three) // '3. eat lunch'
   
   const four = await goToBed()
   console.log(four) //'4. goToBed'
 }
 
 result();
 //'1. go to codestates'
 //'2. sit and code'
 //'3. eat lunch'
 //'4. goToBed'

await로 비동기 함수들을 마치 동기적 program인것처럼 사용. 

await은 항상 async 필요하다. 

setTimeout의 시간이 다 달라도 이 순서대로 나온다.