num_to_roman_converter

function to_roman(input) {
  var romans = ['M', 'CM', 'D', 'CD', 'C', 'XC', 'L', 'XL', 'X', 'IX', 'V', 'IV', 'I'];
  var decimals = [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4,  1];
  var result_roman = '';
  var result_num = 0
  
  if(isNaN(input) === false){
    for(var i = 0 ; i < romans.length ; i++){
      while(input >= decimals[i]){
        result_roman += romans[i];
        input -= decimals[i];
      }
    }
    return result_roman;
  }else{
    for (var i = 0 ; i <= decimals.length ; i++) {
      while(input.indexOf(romans[i]) === 0){
        result_num += decimals[i];
        input = input.replace(romans[i], '');
      }
    }
    return result_num
  }
}

console.log(to_roman("XXXVIII"))
console.log(to_roman(1999))