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>");
                     }
                 }

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