const sumAll = function (numStart, numEnd) { // final sum variable let sum = 0; if (numStart < 0 || numEnd < 0 || typeof numStart != "number" || typeof numEnd != "number") { return "ERROR"; } else if (numStart > numEnd) { [numStart, numEnd] = [numEnd, numStart]; } for (let i = numStart; i <= numEnd; i++) { sum += i; } return sum; }; module.exports = sumAll;