JavaScript: Perform left-to-right function composition for asynchronous functions

JavaScript fundamental (ES6 Syntax): Exercise-166 with Solution

Write a JavaScript program to perform 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.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
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)
})();

Sample Output:

15

Flowchart:

Live Demo:

See the Pen javascript-fundamental-exercise-166 by w3resource (@w3resource) on CodePen.

Improve this sample solution and post your code through Disqus

Previous: Write a JavaScript program to perform left-to-right function composition.
Next: Write a JavaScript program to calculate how many numbers in the given array are less or equal to the given value using the percentile formula.