SelectedChangeEvent for dropdownlist

   <asp:DropDownList ID="ddlValue" runat="server"  CssClass="ddl"
                                                                            Width="325px" TabIndex="1" onchange="ResetValue();">
                                                                        </asp:DropDownList>


 function ResetValue()
    {   
    var txtValue = document.getElementById('<%=txtValue.ClientID%>');
    txtValue.value = '';  
    }