javascript รับค่า เป็น underfined ครับ จาก code behide C#

  string Username, Password;
            Username = txtUserName.Text.Trim();
            Password = txtPassword.Text.Trim();
            if (Username == "admin" && Password == "password")
            {
                Session["User"] = "admin";
                Session["Role"] = "admin";

                ScriptManager.RegisterStartupScript(Page, typeof(Page), "Loginvalid", "Test('assd')", true);
                Response.Redirect("PageControlElectric.aspx");
            }