c# - Cant get dropdown selected value with javascript? -

my drop down(populated objectdatasource):

<asp:dropdownlist runat=server id="ddlusertypes" datasourceid="odsusertypes" appenddatabounditems=true datatextfield="usertype" datavaluefield="usertype"> <asp:listitem value="">-please select one-</asp:listitem> </asp:dropdownlist> 

javascript function getting selected value of dropdown:

<script type="text/javascript" language="javascript">     var notregistered = false;     var email = '';     var usertype = document.getelementbyid("ddlusertypes");     var pow = usertype.options[usertype.selectedindex].value;     function preregister() {debugger;         if (notregistered) {             location.href = '/register.aspx?pageid=<%= confighelper.registrationpageid %>&email=' + encodeuricomponent(email)+'&asd='+encodeuricomponent(pow);             return false;         }         return true;     } </script> 

but not working pow keeps on returning undefined? may because user type doesnt seem assigned stays null? know why code not working?

use hope it's working.

var e = document.getelementbyid("ddlusertypes"); var struser = e.options[e.selectedindex].value;