Composing async functions

const composeAsync = (...funcs) =>
  arg => funcs.reduceRight(async (acc, fn) => fn(await acc), arg);


async function double(v) {
  await new Promise(resolve => setTimeout(resolve, 1000));
  console.log(v);
  return v * 2;
}

composeAsync(double, double, double)(1)
  .then(console.log, console.error);

• The reducer returns a Promise. So getting a value from the acc have to use the await keyword.
• An initial value of the acc may be not a Promise. But it is not a problem, because the await keyword can accept a value other than a Promise.