I want Access ListBox Items In JavaScript Function

function Keydowned(t) {

     //How To Accsess Whole Items Of ListBox In This Section

   }

<input id="TextBox_Tag" type="text"  class="TextBox_Tag_Style" onkeydown="Keydowned(this)" />
                               <asp:ListBox ID="ListBox_Tag" runat="server" CssClass="ListBox_Tag_Position" ondblclick="DblClick(this)">
                                   <asp:ListItem>ab</asp:ListItem>
                                   <asp:ListItem>abc</asp:ListItem>
                                   <asp:ListItem>abcd</asp:ListItem>
                                   <asp:ListItem>ad</asp:ListItem>
                                   <asp:ListItem>abd</asp:ListItem>
                               </asp:ListBox>