隐藏时重置下拉菜单

Question

I have a form that utilizes a drop-down menu that is toggled by radio buttons. However I'm trying to clear the menu selection if the menu is hidden. I'm using JavaScript to show/hide the drop-down but I can't seem to get the drop-down menu to clear when hidden.

This is the JavaScript I have so far, any insights would be appreciated:

<script type="text/javascript">
                        if(document.readyState === "complete")
                        {
                            if (document.getElementById('yesCheck').checked) {
                                document.getElementById('DropDownList').style.visibility = 'visible';
                            }
                        }
                        function yesnoCheck() {
                            if (document.getElementById('yesCheck').checked) {
                                document.getElementById('DropDownList').style.visibility = 'visible';
                            }
                            else {
                                document.getElementById('DropDownList').style.visibility = 'hidden';
                                var elements = document.getElementById("DropDown").options;

                                for(var i = 0; i < elements.length; i++){
                                  elements[i].selected = null;
                                }
                            }
                        }   

Answer 1

Try this one

document.getElementById("DropDownList").selectedIndex = "0";

http://www.w3schools.com/jsref/prop_select_selectedindex.asp