Mastering JavaScript Functional Programming - Second Edition

Calculating several values at once

What would you do if, instead of a single value, you needed to calculate two or more results? This would seem to be a case for providing a clear advantage for common loops, but there's a trick that you can use. Let's yet again revisit the average calculation. We might want to do it the old-fashioned way, by looping and at the same time summing and counting all numbers. Well, reduce() only lets you produce a single result, but there's no reason you can't return an object with as many fields as desired:

const average3 = arr => {  const sumCount = arr.reduce(    (accum, value) => ({sum: value + accum.sum, count: accum.count + 1}),    {sum: 0, count: 0}  );  return sumCount.sum / sumCount.count;};console.log(average3(myArray) ...