closure vs class

var fibo = (function(){
    var buffer = [0,1];
    function f (n) {
        if(buffer[n] == null){
            var recur = f(n-1)+f(n-2);
            buffer[n] = recur;
            return recur;
        }else{
            return buffer[n]; 
        }
    }
    return f;
})();