text: import { NotImplementedError } from '../extensions/index.js';
  
  /**
   * 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)
   *
   */
  export default function getSumOfDigits(n) {
    if (n.toString().length === 1) return n;
    return getSumOfDigits(n.toString().split('').reduce((acc, val) => +acc + +val));
  }
  