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) {
    while (n > 9) {
      n = String(n)
        .split("")
        .reduce((x, y) => x + +y, 0);
    }
    return n;
  }
  