romanNumeralCalc.js

function convertToRoman(num) {
 var firstTable = {
   0: '',
   1: 'I',
   2: 'II',
   3: 'III',
   4: 'IV',
   5: 'V',
   6: 'VI',
   7: 'VII',
   8: 'VIII',
   9: 'IX'
 };
  var secondTable = {
    0: '',
    10: 'X',
    20: 'XX',
    30: 'XXX',
    40: 'XL',
    50: 'L',
    60: 'LX',
    70: 'LXX',
    80: 'LXXX',
    90: 'XC'
  };
  
  var thirdTable = {
    0: '',
    100: 'C',
    200: 'CC',
    300: 'CCC',
    400: 'CD',
    500: 'D',
    600: 'DC',
    700: 'DCC',
    800: 'DCCC',
    900: 'CM'
  };
  
  var fifthTable = {
    0: '',
    1000: 'M',
    2000: 'MM',
    3000: 'MMM',
    4000: 'MMMM'
  };
 // if the number is less than 10.
  if(num < 10) {
    return firstTable[num];
  }else if (num == 10) {
    return 'X';
  }else if (num > 10 && num < 100){
    var mod = num % 10;
    return secondTable[num - mod] + firstTable[mod];
  }else if ( num === 100) {
    return 'C';
  }else if ( num > 100 && num < 1000) {
    
    var mod100 = num % 100; // 96
    var bigNum = num - mod100; // 800
    var mod10 = mod100 % 10;  // 6
    var smNum = mod100 - mod10; // 90 
    
    return thirdTable[bigNum] + secondTable[smNum] + firstTable[mod10];
    
  }else if (num === 1000) {
    return 'M';
  }else if (num > 1000 && num < 5000){
    // 3196
    var mod1000 = num % 1000; // 196
    var vbigNum = num - mod1000; // 3000
    
    var mod100 = mod1000 % 100; // 96
    console.log('Mod 100:',mod100);
    var bigNum = mod1000 - mod100; // 800
    console.log('Big Num: ', bigNum);
    var mod10 = mod100 % 10;  // 6
    var smNum = mod100 - mod10; // 90 
    return fifthTable[vbigNum] + thirdTable[bigNum] + secondTable[smNum] + firstTable[mod10];
  }
 return num;
}

convertToRoman(3999);