kata_js_RomanNumerals.js

// https://www.codewars.com/kata/51b66044bce5799a7f000003/train/javascript
    
const values = {M: 1000,CM: 900, D: 500,CD: 400,C: 100,XC: 90, L: 50, XL: 40,X: 10,IX: 9,V: 5,IV: 4,I: 1 }
const orders = ['M','CM','D','CD','C','XC','L','XL','X','IX','V','IV','I'];

function RomanNumerals(){};
RomanNumerals.toRoman = function(num) {
      let roman = ''
      for (const symbol of orders) {
        while (num >= values[symbol]) {
          roman += symbol
          num -= values[symbol]
        }
      }
      return roman
};
RomanNumerals.fromRoman = function(romanNumber) {
      let prev = ' '

      let sum = 0
    
      let newPrev = 0
      for (let i = romanNumber.length - 1; i >= 0; i--) {
        const c = romanNumber.charAt(i)
    
        if (prev !== ' ') {
          newPrev = values[prev] > newPrev ? values[prev] : newPrev
        }
    
        const currentNum = values[c]
        if (currentNum >= newPrev) {
          sum += currentNum
        } else {
          sum -= currentNum
        }
    
        prev = c
      }
      return sum
};

console.log(RomanNumerals.toRoman(1000), 'M');
console.log(RomanNumerals.toRoman(4), 'IV');
console.log(RomanNumerals.toRoman(1), 'I');
console.log(RomanNumerals.toRoman(1990), 'MCMXC');
console.log(RomanNumerals.toRoman(2008), 'MMVIII');

console.log(RomanNumerals.fromRoman('XXI'), 21);
console.log(RomanNumerals.fromRoman('I'), 1);
console.log(RomanNumerals.fromRoman('IV'), 4);
console.log(RomanNumerals.fromRoman('MMVIII'), 2008);
console.log(RomanNumerals.fromRoman('MDCLXVI'), 1666);