Error not getting displayed

Question

User-1499457942 posted

Hi

  I am trying below code but error is not getting displayed if there is some error. For e.g i have written below line and it should display error on Client Side

Request.QueryString["tmp"] != "ABC"

try
        {
            con.ConnectionString = ConfigurationManager.ConnectionStrings["cnn"].ConnectionString;
            if (Request.QueryString["tmp"] != null && Request.QueryString["tmp"].ToString() != "")
            {
                if (!Page.IsPostBack)
                {
                    con.Open();
                }
            }
        }
        catch (Exception ex)
        {
            string message = ex.ToString();
            System.Text.StringBuilder sb = new System.Text.StringBuilder();
            sb.Append("<script type = 'text/javascript'>");
            sb.Append("window.onload=function(){");
            sb.Append("alert('");
            sb.Append(message);
            sb.Append("')};");
            sb.Append("</script>");
            ClientScript.RegisterClientScriptBlock(this.GetType(), "alert", sb.ToString());
        }

Thanks