Number <=> Roman

roman-util

const converter = (() => {
  const romanMap = [[1000, 'M'], [900, 'CM'], [500, 'D'], [400, 'CD'], [100, 'C'], [90, 'XC'],
    [50, 'L'], [40, 'XL'], [10, 'X'], [9, 'IX'], [5, 'V'], [4, 'IV'], [1, 'I']];
  
  const toRoman = num => {
    let remainingNum = num;
    return romanMap.reduce((roman, map) => {
      while (remainingNum % map[0] < remainingNum) {
        roman += map[1];
        remainingNum -= map[0];
      }
      return roman;
    }, '');
  };
  
  const fromRoman = str => {
    let remainingStr = str;
    return romanMap.reduce((num, map) => {
      while (remainingStr.indexOf(map[1]) === 0) {
        num += map[0];
        remainingStr = remainingStr.replace(map[1], '');
      }
      return num;
    }, 0);
  }

  return { toRoman, fromRoman};
})();

converter.toRoman(2018); // 'MMXVIII'
converter.fromRoman('MMXVIII'); // 2018