Ajax Loading Bar?

Ajax Loading Bar?

 $(document).ready(function() {
        $("select[name='month']").change(function() {
            var infom = $("select[name='month']").val();

            $.ajax({
                url: "documents/getinfo",
                type: "POST",
                data: "infom=" + infom,
                success:
                        function(likeResult) {
                            $("#likeResult").html(likeResult).fadeIn("slow");
                        }
            });

        });

    });

I have image - loading.gif
So, how to get when the query is opened and when is done. In this case, i tried with append but doesn't catch when begin the query?