text: /**
   * Given a number, replace this number with
   * the sum of its digits until we get to a one digit number.
   *
   * @param {Number} n
   * @return {Number}
   *
   * @example
   * For 100, the result should be 1 (1 + 0 + 0 = 1)
   * For 91, the result should be 1 (9 + 1 = 10, 1 + 0 = 1)
   *
   */
  function getSumOfDigits(n) {
    const numArr = n.toString().split('');
    const sum = (arr) => arr.reduce((a, b) => Number(a) + Number(b));
    const res = sum(numArr);
    if (res <= 9) {
      return res;
    }
    return getSumOfDigits(res);
  }
  
  module.exports = getSumOfDigits;
  