post a data from database to a html in code behind without using AJAX

function BindTable() {

           $.ajax({
               type: "POST",
               url: "newsCafe.aspx/GetData",
               contentType: "application/json;charset=utf-8",
               data: {},
               dataType: "json",
               success: function (data) {

                   $("#grdDemo").empty();

                   if (data.d.length > 0) {
                       $("#grdDemo").append("<tr><th>Username</th>
                       <th>Firstname</th>  <th>Lastname</th>
                       <th>EmailID</th></tr>");
                       for (var i = 0; i < data.d.length; i++) {

                           $("#grdDemo").append("<tr><td>" +
                           data.d[i].Firstname + "</td> <td>" +
                           data.d[i].Lastname + "</td> <td>" +
                           data.d[i].Username + "</td> <td>" +
                           data.d[i].EmailID + "</td></tr>");
                       }
                   }
               },
               error: function (result) {
                   //alert("Error login");

               }
           });

<div id="grdDemo"> </div>

[WebMethod] 
        public static DetailsClass[] GetData() //GetData function
        {
            List<detailsclass> Detail = new List<detailsclass>();

            string SelectString = "Select Username,Firstname,Lastname,EmailID from DemoTable";
            SqlConnection cn = new SqlConnection("Data Source=servername;
            Initial Catalog=DemoDatabase;User ID=User;Password=*****");
            SqlCommand cmd = new SqlCommand(SelectString,cn);
            cn.Open();

            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataTable dtGetData = new DataTable();

            da.Fill(dtGetData);

            foreach(DataRow dtRow in dtGetData.Rows)
            {
                DetailsClass DataObj = new DetailsClass();
                DataObj.Username = dtRow["Username"].ToString();
                DataObj.Firstname = dtRow["Firstname"].ToString();
                DataObj.Lastname = dtRow["Lastname"].ToString();
                DataObj.EmailID = dtRow["EmailID"].ToString();

                Detail.Add(DataObj);            
            }

            return Detail.ToArray();
        }
        public class DetailsClass //Class for binding data
        {
            public string Username { get; set; }
            public string Firstname { get; set; }
            public string Lastname { get; set; }
            public string EmailID { get; set; }
        
        }