let romanNumber = new Map();
romanNumber.set('M', 1000);
romanNumber.set('CM', 900);
romanNumber.set('D', 500);
romanNumber.set('CD', 400);
romanNumber.set('C', 100);
romanNumber.set('XC', 90);
romanNumber.set('L', 50);
romanNumber.set('XL', 40);
romanNumber.set('X', 10);
romanNumber.set('V', 5);
romanNumber.set('VI', 4);
romanNumber.set('I', 1);

function integerToRoman(number) {
  if(number > 3999 || number < 1) throw new Error('Range 1 to 3999');

  let result = '';
  romanNumber.forEach((value, key) => {
    if(number - value >= 0) {
      result += key;
      number -= value;
    }
  });

  return result;
}

console.log(integerToRoman(49));