Alert message is not displayed using Asp.net ajax

Question

The alert message is not displayed after add record into the database using Asp.net Ajax.record is add into the database successfully.Alert is not displaying. I attached the code below what I tried so far below.after add record how to return to the ajex success function to display alert("success");

Form Design

<form  id="frmProject" runat="server">
            <div>
                <label class="form-label">First Name</label>     
               <input type="text" id="fname" class="form-control"  />
            </div>
            <div class="form-group" align="left">
             <label class="form-label">Age</label>
                <input type="text" id="age" class="form-control"  />
            </div>
            <div> 
               <input type="button" id="b1" value="add" class="form-control" onclick="addProject()" />

            </div>
        </form>

Ajex

  function addProject() {
                $.ajax({
                    type: 'POST',
                    url: 'insert.aspx',
                    dataType: 'JSON',
                    data: {fname: $('#fname').val(), age: $('#age').val()},
                    success: function (data) {         
                        alert("success");
                        get_all();
                    },
                    error: function (xhr, status, error) {
                        console.log(xhr.responseText);
                    }
                });

                }

insert.aspx

 public static string GetData(string fname, int age)
            {
                SqlConnection con = new SqlConnection("server=.; Initial Catalog = jds; Integrated Security= true;");
                string sql = "insert into record values('" + fname + "','" + age + "')";
                SqlCommand cmd = new SqlCommand(sql, con);
                con.Open();
                cmd.ExecuteNonQuery();
                con.Close();
                return HttpContext.Current.Session.SessionID;
            }  

Answer 1

use web method for Ajax request

[WebMethod(EnableSession= true)]
public static string GetData(string fname,int age)    
{    
   // place your logic here
   return HttpContext.Current.Session.SessionID;    
}

Your Ajax request

$('#b1').click(function () {
    jQuery.ajax({
        url: 'insert.aspx/GetData',
        type: "POST",
        data: {fname: $('#fname').val(), age: $('#age').val()},
        dataType: "json",
        contentType: "application/json; charset=utf-8",
        success: function (data) {
            alert(JSON.stringify(data));
        }
    });
});