const nums1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; const nums2 = [99, 77, 55, 66, 33,22,11,15,16]; const nums3 = [11, 12, 13, 14, 15, 16, 17, 18]; const result = [...nums1, ...nums2, ...nums3].reduce((acc, x, i) => acc + x ,0); console.log(result)