algoritma array jumlah maksimum javascript

function maxSumArr(arr, num) {
    let maxSum = 0;
    let tempSum = 0;
    if(arr.length < num) return null;
    for(let i = 0; i < num; i++) {
       tempSum += arr[i];
    }
    tempSum = maxSum;
    for(let i = num; i < arr.length; i++) {
       tempSum = tempSum - arr[i - num] + arr[i];
       maxSum = Math.max(tempSum, maxSum);
       }      
       return maxSum;
}
Donald Obinna Amadi