Async/Await and Promises

async-await-and-promises

const P = val => {
  return new Promise(resolve => {
    setTimeout(() => resolve(val), 1000)
  })
}

const usePromise = () => {
  console.log('start')
 
  P('async val').then(res => {
    console.log(res)
  })

  console.log('stop')
}

const useAsyncAwait = async () => {
  console.log('start')

  const res = await P('async val')
  console.log(res)

  console.log('stop')
}

const useAsyncAwaitWithThen = async () => {
  console.log('start')

  const res = await P('async val').then(res => {
    console.log('inside callback:', res)
    return res
  })
  console.log(res)

  console.log('stop')
}

usePromise() // logs 'start' -> 'stop' -> 'async val'
useAsyncAwait() // logs 'start' -> 'async val' -> 'stop'
useAsyncAwaitWithThen() // logs 'start' -> 'inside callback: async val' -> 'async val' -> 'stop'