What will be the output of the following recursive function?

function computeSum(arr) {
  if (arr.length === 0) {
    return 0;
  }
  let firstElement = arr[0];
  let remainingArray = arr.slice(1);
  if (Array.isArray(firstElement)) {
    return computeSum(firstElement) + computeSum(remainingArray);
  }
  return firstElement + computeSum(remainingArray);
}
console.log(computeSum([1, [2, [3, 4]], 5]));