text: const { NotImplementedError } = require('../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)
   *
   */
  function getSumOfDigits(n) {
    while (n > 9) {
      let sum = 0;
      for (let i = 0; i < String(n).length; i++) {
        sum += Number(String(n)[i]);
      }
      n = sum;
    }
  
    return n;
  }
  
  module.exports = {
    getSumOfDigits,
  };
  