pipeAsyncFunctions

Performs left-to-right function composition for asynchronous functions.

• Use Array.prototype.reduce() and the spread operator (...) to perform function composition using Promise.prototype.then().
• The functions can return a combination of normal values, Promises or be async, returning through await.
• All functions must accept a single argument.

const pipeAsyncFunctions = (...fns) =>
  arg => fns.reduce((p, f) => p.then(f), Promise.resolve(arg));

const sum = pipeAsyncFunctions(
  x => x + 1,
  x => new Promise(resolve => setTimeout(() => resolve(x + 2), 1000)),
  x => x + 3,
  async x => (await x) + 4
);
(async() => {
  console.log(await sum(5)); // 15 (after one second)
})();