Javascript :: pipeAsyncFunctions

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

Use Array.prototype.reduce() with the spread operator (...) to perform left-to-right function composition using Promise.then(). The functions can return a combination of: simple values, Promise‘s, or they can be defined as async ones returning through await. All functions must be unary.

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)
})();

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