hexlet help

hexlet_for_kate.js

const SumOfNum = (str) => {
  let result = 0;
  let i = 0;

  while (str.length > i) {
    result = Number(str[i]) + Number(result);
    i += 1;
  }

  if (String(result).length > 1) {
    result = SumOfNum(String(result));
  }

  return result;
}

const addDigits = (num) => {
  let result = num;
  result = SumOfNum(String(result));

  return result;
}
console.log(SumOfNum('4687867457'));