function convertToRoman(num) {
  let numArr = num.toString().split("");
  let numSize = numArr.length;

  let onesArr = ['I', 'II', 'III', 'IV', 'V', 'VI', 'VII', 'VIII', 'IX'];
  let tensArr = ['X', 'XX', 'XXX', 'XL', 'L', 'LX', 'LXX', 'LXXX','XC'];
  let hundredsArr = ['C', 'CC', 'CCC', 'CD', 'D', 'DC', 'DCC', 'DCCC','CM'];
  let thousandsArr = ['M', 'MM', 'MMM', 'MMMM'];

  if(numSize === 1){
    return oneDigitToRoman(numArr[0], onesArr);
  }
  else if(numSize === 2){
    return oneDigitToRoman(numArr[0], tensArr)
          + oneDigitToRoman(numArr[1], onesArr);
  }
  else if(numSize === 3){
    return oneDigitToRoman(numArr[0], hundredsArr)
      + oneDigitToRoman(numArr[1], tensArr)
      + oneDigitToRoman(numArr[2], onesArr);
  }
  else if(numSize === 4){
  return oneDigitToRoman(numArr[0], thousandsArr)
    + oneDigitToRoman(numArr[1], hundredsArr)
    + oneDigitToRoman(numArr[2], tensArr)
    + oneDigitToRoman(numArr[3], onesArr);
  }
}

function oneDigitToRoman(num, arr){
  if(num == 0){
    return "";
  }
  return arr[num - 1];
}

convertToRoman(36);