AJAX - BeforeSend总是在发送之前立即运行

Question

请参阅以下代码：

function GetSQLTable() {

            var str = $("#<%=fieldGroupReferences.ClientID%>")[0].value
            var res = str.split(",");
            var numSucceeded = 0;
            $("#LoadingImage").show();
            $("#LoadingImage2").show();
            for (var i = 0; i < res.length; i++) {
                var div = document.createElement('div');
                div.id = "div" + i
                document.getElementById('info_div').appendChild(div);

                var PossiblesPage = false;
                $.ajax({
                    type: "POST",
                    url: "PrimaryNominalAjax.aspx/GetSQLTable",
                    data: '{username: "' + $("#<%=fieldUserName.ClientID%>")[0].value + '", terminalname: "' + $("#<%=fieldTerminalName.ClientID%>")[0].value + '", terminalip: "' + $("#<%=fieldTerminalIP.ClientID%>")[0].value + '", mappingid: "' + res[i] + '", usergroup: "' + $("#<%=fieldUserGroup.ClientID%>")[0].value + '", usn: "' + $("#<%=fieldUSN.ClientID%>")[0].value + '", requester: "' + $("#<%=fieldRequester.ClientID%>")[0].value + '", reason: "' + $("#<%=fieldReason.ClientID%>")[0].value + '", rrd: "' + $("#<%=fieldRRD.ClientID%>")[0].value + '", review: "' + $("#<%=fieldReview.ClientID%>")[0].value + '", possibles: "' + PossiblesPage + '",linkno: "", urn1: "", urn2: ""}',
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    success: OnSuccess(i, res.length),
                    failure: function (response) {
                        alert('there was an error loading the webpage')
                    }
                });
            }
            function OnSuccess(i, totalrows) {
                return function (response) {
                alert(response.d)
             }}

Ajax多次运行。我想在运行e.g. mappingID + " is currently running"之前将映射ID打印到屏幕。在AJAX请求期间，MappingID被传递给服务器。是否有一个事件可以让我处理这个要求？我看过这里：http://api.jquery.com/Ajax_Events/。请问BeforeSend处理它吗？也就是说，BeforeSend总是在AJAX请求之前立即运行，即我现在希望这种情况发生：

Before Send MappingID 1
Before Send MappingID 2
Send MappingID 1
Send MappingID 2