How to validate a textarea in a form.i.e, it should not be empty or have any new lines and if so raise an alert

   <script>
    function val()
    {
      //ifnewline found or blank raise an alert
    } 
   </script>
   <form>  
   <textarea name = "pt_text" rows = "8" cols = "8" class = "input" WRAP ></textarea>
   <input type=""button" onclick="val();"
    </form>

Thanks