roman/arabic conversion code kata

gistfile1.txt

// while reading: http://compositecode.com/2011/09/27/code-katas-kicking-off-with-a-little-javascript/

function romanToArabic(roman) {
   var letters = ["M", "D", "C", "L", "X", "V", "I"],
       values = { M: 1000, D: 500, C: 100, L: 50, X: 10, V: 5, I: 1 },
       sum = 0;
   for(var i=0; i<roman.length; i++) {
        if (typeof roman[i+1]!= "undefined" && letters.indexOf(roman[i]) > letters.indexOf(roman[i+1]) ) {
            sum += values[roman[i+1]] - values[roman[i]];
            i++;
        } else {
            sum += values[roman[i]];
        }
   }
   return sum;
}