To sum two arrays in single iteration with JavaScript, we use the map method.

For instance, we write

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

const sum = array1.map((num, idx) => {
  return num + array2[idx];
});

to call array1.map with a callback that returns the sum of num and item in array2 at the same idx index.

The array with the sums is returned.