To download csv as post in ASP.NET MVC5

// Here's an excerpt:
$('#download').click(
            function(){
                var param = new Object();
                //param set
                if(parking!=null){
                    $.ajax({
                        type: "POST",
                        url: "@Url.Action("CreateCsv", "Csv")",
                        data —JSON.stringify (param),
                        contentType: "application/json; charset=utf-8",
                        datatype: 'json',
                        success: function() {
                            debugger
                            alert("success");
                        },
                        failure:function(data){
                            debugger
                            alert(data.StatusMessage);
                        },
                        error: function(data){
                            debugger
                            alert(data.StatusMessage);
                        }
                    })
                }
            }
        );


[HttpPost]
        public ActionResult CreateCsv (Param Pram)
        {
            if(Request.IsAjaxRequest())
            {

                // Retrieving data from DB

                // CSV Content Generation

                 varfileName=string.Format("filename_{0}.csv", DateTime.Now.ToString("yyyyMMddHHmmss"));

                vardata=Encoding.UTF8.GetBytes(csvString);

                varstream=new MemoryStream(data);
                var writer = new StreamWriter(stream);

                // var fileStreamResult = new FileStreamResult (stream, System.Net.Mime.MediaTypeNames.Text.Plain);
                // fileStreamResult.FileDownloadName=fileName;

                // return fileStreamResult;

                writer.Write(data);
                writer.Flush();
                stream.Position=0;

                return File (stream, "text/csv", fileName);

            }
            return null;
        }