JSFiddle - React, Tailwind, and code Playground

JavaScript

Array.prototype.SumArray = function (arr) {
    var sum = [];
    if (arr != null && this.length == arr.length) {
        for (var i = 0; i < arr.length; i++) {
            sum.push(this[i] + arr[i]);
        }
    }

    return sum;
}

var array1 = [1, 2, 3, 4];
var array2 = [5, 6, 7, 8];
var sum = array1.SumArray(array2);
console.log(sum);