Ajax 实现长轮询（long-polling）

<script language="javascript" type="text/javascript">
    var updater = {
        poll: function() {
            $.ajax({ url: "Handler1.ashx",
                type: "POST",
                dataType: "text",
                success: updater.onSuccess,
                error: updater.onError
            });
        },
        onSuccess: function(data, dataStatus) {
            try {
                $("p").append(data + "<br>");
            }
            catch (e) {
                updater.onError();
                return;
            }
            interval = window.setTimeout(updater.poll, 0);
        },
        onError: function() {
            console.log("Poll error;");
        }
    };
    updater.poll();
</script>