sum-of-digits-slash-digital-roots.js

/*
  INSTRUCTIONS
  =============================================================
  In this kata, you must create a digital root function.
  A digital root is the recursive sum of all the digits in a number. Given n, take the sum of the digits of n. If that value has two digits, continue reducing in this way until a single-digit number is produced. This is only applicable to the natural numbers.

  Here's how it works (Ruby example given):

  digital_root(16)
  => 1 + 6
  => 7

  digital_root(942)
  => 9 + 4 + 2
  => 15 ...
  => 1 + 5
  => 6

  digital_root(132189)
  => 1 + 3 + 2 + 1 + 8 + 9
  => 24 ...
  => 2 + 4
  => 6

  digital_root(493193)
  => 4 + 9 + 3 + 1 + 9 + 3
  => 29 ...
  => 2 + 9
  => 11 ...
  => 1 + 1
  => 2
*/

/*
  MY SOLUTION
*/
function digital_root(n) {
  // Convert to string to split into a array...
  let num = n.toString().split('');
  let answer = 0;
  for(let i = 0; i < num.length; i++) {
    answer += parseInt(num[i], 10);
  }
  if(answer <= 9) {
    // Single Digit
    return answer;
  } else {
    // Multiple Digits - Continuing summing...
    return digital_root(answer);
  }
}