Javascript - Sum two arrays in single iteration

I know this is an old question but I was just discussing this with someone and we came up with another solution. You still need a loop but you can accomplish this with the Array.prototype.map().

var array1 = [1,2,3,4];
var array2 = [5,6,7,8];

var sum = array1.map(function (num, idx) {
  return num + array2[idx];
}); // [6,8,10,12]

Here is a generic solution for N arrays of possibly different lengths.

It uses Array.prototype.reduce(), Array.prototype.map(), Math.max() and Array.from():

function sumArrays(...arrays) {
  const n = arrays.reduce((max, xs) => Math.max(max, xs.length), 0);
  const result = Array.from({ length: n });
  return result.map((_, i) => arrays.map(xs => xs[i] || 0).reduce((sum, x) => sum + x, 0));
}

console.log(...sumArrays([0, 1, 2], [1, 2, 3, 4], [1, 2])); // 2 5 5 4

var arr = [1,2,3,4];
var arr2 = [1,1,1,2];

var squares = arr.map((a, i) => a + arr2[i]);

console.log(squares);