ajax请求加载Loading或错误提示

    <div id="loadingDiv" style="color:#f39800;">Loading...</div>

<script type="text/javascript">

    var $loading = $('#loadingDiv').hide();
        $(document).ajaxStart(function () {
              $('#loadingDiv').css("position", "absolute");
              $('#loadingDiv').css("top", Math.max(, (($(window).height() - $('#loadingDiv').outerHeight()) / ) +
                                                        $(window).scrollTop()) + "px");
              $('#loadingDiv').css("left", Math.max(, (($(window).width() - $('#loadingDiv').outerWidth()) / ) +
                                                        $(window).scrollLeft()) + "px");
              $('#loadingDiv').show();
          })
          .ajaxStop(function () {
              $('#loadingDiv').hide();
          });
        $(document).ajaxError(function (event, jqXHR, request, settings) {
            var text = jqXHR.statusText + "(" + jqXHR.status + ")";
            if (jqXHR.responseJSON)
                text = jqXHR.responseJSON.message;
             alert('操作出现异常：' + text + '重试后仍出现请联系开发');
        });
</script>