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) {
    let sum = 0
    let str = n.toString()
    str = str.split('').reduce((previousValue, currentValue) => +previousValue + +currentValue, sum)
    if (str>9){
    return getSumOfDigits(str)
    } else {
    return str
    }
  }
  
  module.exports = {
    getSumOfDigits
  };
  