run asynchronous task parallel or series

async_await_parallel_series.js

const wait = delay => {
  return () => new Promise(resolve => {
    setTimeout(() => {
      console.log(`wait ${delay}ms`)
      resolve()
    }, delay)
  })
}

const wait200 = wait(200)
const wait500 = wait(500)
const wait1000 = wait(1000)

const parallel = async () => {
  const start = new Date()
  await Promise.all([wait200(), wait500(), wait1000()])
  console.log(`total ${new Date() - start}ms`)
}

const series = async () => {
  const start = new Date()
  await wait200()
  await wait500()
  await wait1000()
  console.log(`total ${new Date() - start}ms`)
}

if (process.argv[2] === 'parallel') return parallel()
series()