async function

async function name([param[, param[, ... param]]]) {
   statements
}

function resolveAfter2Seconds(x) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(x
    }, 2000
  }
}


async function add1(x) {
  const a = await resolveAfter2Seconds(20
  const b = await resolveAfter2Seconds(30
  return x + a + b;
}

add1(10).then(v => {
  console.log(v  // prints 60 after 4 seconds.
}


async function add2(x) {
  const p_a = resolveAfter2Seconds(20
  const p_b = resolveAfter2Seconds(30
  return x + await p_a + await p_b;
}

add2(10).then(v => {
  console.log(v  // prints 60 after 2 seconds.
}

function getProcessedData(url) {
  return downloadData(url) // returns a promise
    .catch(e => {
      return downloadFallbackData(url // returns a promise
    })
    .then(v => {
      return processDataInWorker(v // returns a promise
    }
}

async function getProcessedData(url) {
  let v;
  try {
    v = await downloadData(url 
  } catch(e) {
    v = await downloadFallbackData(url
  }
  return processDataInWorker(v
}