conversion for single digits

app.js

var App = {
    ...
    convertArabicToRoman = function( arabic ) {
    var i = parseInt( arabic, 10 );
      switch( i ) {
          case 1: return "I";
          case 2: return "II";
          case 3: return "III";
          case 4: return "IV";
          case 5: return "V";
          case 6: return "VI";
          case 7: return "VII";
          case 8: return "VIII";
          case 9: return "IX";
      }
      return "";
    }
    ...
}