function toRoman(num) {
  let result = '';
  const decimal = [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1];
  const roman = ["M", "CM","D","CD","C", "XC", "L", "XL", "X","IX","V","IV","I"];
  for (let i = 0;i<=decimal.length;i++) {
    while (num%decimal[i] < num) {
      result += roman[i];
      num -= decimal[i];
    }
  }
  return result;
}

toRoman(123); //returns "CXXIII"
toRoman(3290); // returns "MMMCCXC"
toRoman(777); // returns "DCCLXXVII"
toRoman(949); // returns "CMXLIX"
toRoman(2000); // returns "MM"