convert-to-roman.js

/**
 * Convert the given number num into a roman numeral. This function
 * supports converting numbers in between 1 and 3999 into roman numerals.
 * @param {*Number} num A number to be converted into a roman number.
 * @returns The roman numeral string of the given num.
 */
function convertToRoman(num) {
  let commonNums = [
    {'I': '1'}, {'II': '2'}, {'III': '3'}, {'IV': '4'}, {'V': '5'},
    {'VI': '6'}, {'VII': '7'}, {'VIII': '8'}, {'IX': '9'}, {'X': '10'},
    {'XX': '20'}, {'XXX': '30'}, {'XL': '40'}, {'L': '50'}, {'LX': '60'},
    {'LXX': '70'}, {'LXXX': '80'}, {'XC': '90'}, {'C': '100'},
    {'CC': '200'}, {'CCC': '300'}, {'CD': '400'}, {'D': '500'},
    {'DC': '600'}, {'DCC': '700'}, {'DCCC': '800'}, {'CM': '900'},
    {'M': '1000'}, {'MM': '2000'}, {'MMM': '3000'}
  ];

  // Convert num to a string
  let strNum = num.toString();

  // If strNum is found in commonNums, return its key
  let romanNum = commonNums.filter(prop =>
    strNum == Object.values(prop)
  );
  if (romanNum.length > 0) {
    return Object.keys(romanNum[0])[0];
  }

  // Reset strNum as a string version of num
  strNum = num.toString();

  // Create an array version of strNum
  let arrNum = strNum.split("");

  // If num > 10, pad the numbers greater than 10. Increase by
  // one zero pad with each new iteration.
  if (num > 10) {
    let zero = "";
    let lastNum = arrNum.length;

    arrNum.slice(0, lastNum - 1).map(n => {
      if (lastNum >= 0) {
        zero += "0";
        lastNum--;
        arrNum[lastNum - 1] += zero;
      }
    });
  }

  let value = "";
  let index = 0;

  // Replace arrNum elements with their corresponding roman numerals
  commonNums.filter(n => {
    value = Object.values(n);
    index = arrNum.indexOf(value[0]);

    if(arrNum[index]){ 
      arrNum[index] = Object.keys(n)[0];
    }
  });

  // Join array of roman numerals and remove pure 0 elements
  // that originally 0's found in between the original num.
  // E.g., 501, 1004, 1006, 2014.
  arrNum = arrNum.join("").replace(/0/g, "");

  return arrNum;
}

// Tests
console.log(convertToRoman(2)); // II
console.assert(convertToRoman(2), "should return the string II");

console.log(convertToRoman(3)); // III
console.assert(convertToRoman(3), "should return the string III");

console.log(convertToRoman(4)); // IV
console.assert(convertToRoman(4), "should return the string IV");

console.log(convertToRoman(5)); // V
console.assert(convertToRoman(5), "should return the string V");

console.log(convertToRoman(9)); // IX
console.assert(convertToRoman(9), "should return the string IX");

console.log(convertToRoman(12)); // XII
console.assert(convertToRoman(12), "should return the string XII");

console.log(convertToRoman(16)); // XVI
console.assert(convertToRoman(16), "should return the string XVI");

console.log(convertToRoman(29)); // XXIX
console.assert(convertToRoman(29), "should return the string XXIX");

console.log(convertToRoman(44)); // XLIV
console.assert(convertToRoman(44), "should return the string XLIV");

console.log(convertToRoman(45)); // XLV
console.assert(convertToRoman(45), "should return the string XLV");

console.log(convertToRoman(68)); // LXVIII
console.assert(convertToRoman(68), "should return the string LXVIII");

console.log(convertToRoman(83)); // LXXXIII
console.assert(convertToRoman(83), "should return the string LXXXIII");

console.log(convertToRoman(97)); // XCVII
console.assert(convertToRoman(97), "should return the string XCVII");

console.log(convertToRoman(99)); // XCIX
console.assert(convertToRoman(99), "should return the string XCIX");

console.log(convertToRoman(400)); // CD
console.assert(convertToRoman(400), "should return the string CD");

console.log(convertToRoman(500)); // D
console.assert(convertToRoman(500), "should return the string D");

console.log(convertToRoman(501)); // DI
console.assert(convertToRoman(501), "should return the string DI");

console.log(convertToRoman(649)); // DCXLIX
console.assert(convertToRoman(649), "should return the string DCXLIX");

console.log(convertToRoman(798)); // DCCXCVIII
console.assert(convertToRoman(798), "should return the string DCCXCVIII");

console.log(convertToRoman(891)); // DCCCXCI
console.assert(convertToRoman(891), "should return the string DCCCXCI");

console.log(convertToRoman(1000)); // M
console.assert(convertToRoman(1000), "should return the string M");

console.log(convertToRoman(1004)); // MIV
console.assert(convertToRoman(1004), "should return the string MIV");

console.log(convertToRoman(1006)); // MVI
console.assert(convertToRoman(1006), "should return the string MVI");

console.log(convertToRoman(1023)); // MXXIII
console.assert(convertToRoman(1023), "should return the string MXXIII");

console.log(convertToRoman(2014)); // MMXIV
console.assert(convertToRoman(2014), "should return the string MMXIV");

console.log(convertToRoman(3999)); // MMMCMXCIX
console.assert(convertToRoman(3999), "should return the string MMMCMXCIX");