Kata solution of https://www.codewars.com/kata/roman-numerals-helper

roman-numerals.js

var RomanNumerals = {
  fromRoman: function(roman) {
    var map = {IV:4,IX:9,XL:40,XC:90,CD:400,CM:900,I:1,V:5,X:10,L:50,C:100,D:500,M:1000};
    var value = 0;
    for (var i = 0; i < roman.length; i++) {
      var two = map[roman[i]+roman[i+1]], one = map[roman[i]];
      if (two != null) { value += two; i++; }
      else if (one != null) value += one;
    }
    return value;
  },
  toRoman: function(value) {
    var map = {M:1000,CM:900,D:500,CD:400,C:100,C:100,XC:90,L:50,XL:40,X:10,IX:9,V:5,IV:4,I:1};
    var roman = '';
    while (value > 0) {
      for (var r in map) {
        if (map[r] <= value) {
          roman += r;
          value -= map[r];
          break;
        }
      }
    }
    return roman;
  }
};