I've been working on numerals conversion lately. Now the JavaScript course I'm following asked me to do something similar for Roman numerals.

To keep things fresh and given the amount of test-cases provided I decided to write this one Test-Driven Development style. That is, for as much as I understand it.

First I check whether it's dividable by a full numeral (M, C, etc.). After that I have to reverse the string because the numerals were added in reverse order. The next step is to translate all combinations into their correct form using regex and a translation map. The functions were written in that order and fixing the problem the last part caused.

So far it looks very messy. Is this how one is supposed to solve problems TDD style? There is definitely a lot of code duplication going on, could this be fixed with another map?

Challenge

Convert the given number into a Roman numeral.

All Roman numerals answers should be provided in upper-case.

Test cases

convert(5) // "V".
convert(9) // "IX".
convert(12) // "XII".
convert(16) // "XVI".
convert(29) // "XXIX".
convert(44) // "XLIV".
convert(45) // "XLV"
convert(68) // "LXVIII"
convert(83) // "LXXXIII"
convert(97) // "XCVII"
convert(99) // "XCIX"
convert(500) // "D"
convert(501) // "DI"
convert(649) // "DCXLIX"
convert(798) // "DCCXCVIII"
convert(891) // "DCCCXCI"
convert(1000) // "M"
convert(1004) // "MIV"
convert(1006) // "MVI"
convert(1023) // "MXXIII"
convert(2014) // "MMXIV"
convert(3999) // "MMMCMXCIX"

Code

function convert(num) {
  roman = "";
  for (var i = 0; i < num; i++) {
    //MDCLXVI
    if (!(num % 1000)) { roman += "M"; num -= 1000; }
    else if (!(num % 500)) { roman += "D"; num -= 500; }
    else if (!(num % 100)) { roman += "C"; num -= 100; }
    else if (!(num % 50)) { roman += "L"; num -= 50; }
    else if (!(num % 10)) { roman += "X"; num -= 10; }
    else if (!(num % 5)) { roman += "V"; num -= 5; }
    else if (!(num % 1)){ roman += "I"; num -= 1; }
  }
  roman = roman.split('').reverse().join('');
  var translationMap = {
    DCCCC : 'CM',
    CCCC : 'CD',
    LXXXX : 'XC',
    XXXX : 'XL',
    VIIII : 'IX',
    IIII : 'IV',
  };
  for (var i in translationMap) {
    roman = roman.replace(new RegExp(i,'g'), translationMap[i]);
  }
  return roman;
}

convert(3999);

Run it at repl.it