I want to get the value of the select box using javascript i have the following code.

html part

<select name=marked id=marked onchange=checkdata(this); >

        <option value=>SELECT</option>

        <option value=all>ALL</option>

        <option value=none>NONE</option>

        <option value=read>READ</option>

        <option value=unread>UNREAD</option>

        </select>

script

<script type=text/javascript>

         function checkdata()

         {

             for(var i=0; i < document.myform.message.length; i++)

             {

                 document.myform.message[i].checked=true;

             }

         }

    </script>

i tried the code

var all = document.myform.marked.options[document.myform.selectedIndex].value;

             alert(all);

no alert is coming

i also tried

 var all= document.getElementById('marked').value;

             alert(all);

alert is coming but the value for every selection in 1