gistfile1.js

foldR: function(str, acc, fun) {
  var i, 
      len = str.length,
  for(i = 0; i < len; i++) {
    acc = fun(acc, str.substring(len-i-1,len-i));
  }
}

isCreditCard( CC ) {
     if (CC.length > 19)
          return (false);

     var sum, 
         mul = 1,
         tproduct;

     sum = foldR(CC, 0, function(acc, digit) {
          tproduct = parseInt(digit,10)*mul;
          if (mul == 1)
               mul++;
          else
               mul--;
          if (tproduct >= 10)
               return(acc + (tproduct % 10) + 1);
          else
               return(acc + product);
     }
     if ((sum % 10) == 0)
          return (true);
     return (false);
}