without refresh web page display alert box

how to display without page refresh display alert box

my code

  if (Icollection.Count == 0)

                 {

                     Response.Write("<script>alert('no data');</script>");

                 }

                 else

                 {

                     foreach (SearchBo search in Icollection)

                     {

                         string fname = search.Filename;

                         int id = search.E_id;

                         Response.Write("<script>alert('" + fname + "');</script>");

                     }

                 }