258.js

/** ------------------------------------------------------------------------------
 * 
 * 2023-04-26
 * 258. Add Digits
 * https://leetcode.com/problems/add-digits/
 * 
 ------------------------------------------------------------------------------ */
var addDigits = function (num) {
  if (num < 10) {
    return num;
  } else {
    num = [...num.toString()].reduce((a, c) => a + Number(c), 0);
    return addDigits(num);
  }
};

// 미친풀이
var addDigits = function (num) {
  return ((num - 1) % 9) + 1;
};

console.log(addDigits(38));