Get MultiSelect Item , ContextMenu ?

[Mohammad]

My Code is the following :

function MultiSelect_ContextMenu_BeforeShow(e) {

    var contextMenu = Ext.getCmp('<%= MultiSelect_ContextMenu.ClientID %>');
    var multiSelect = Ext.getCmp('<%= MultiSelect1.ClientID %>');

    //***********

}

<ext:Panel ID="Panel9" runat="server" Title=" Users " Height="200" Width="400"
StyleSpec="margin:0 auto;">
<Items>
    <ext:MultiSelect ID="MultiSelect1" runat="server" Height="200" Width="400" StyleSpec="margin:0 auto;"
        ContextMenuID="MultiSelect_ContextMenu">
        <Items>
        </Items>
    </ext:MultiSelect>
</Items>
</ext:Panel>

<ext:Menu ID="MultiSelect_ContextMenu" runat="server">
    <Items>
        <ext:MenuItem ID="MenuItem_Delete" runat="server" Text=" Delete " Icon="Delete" />
    </Items>
    <Listeners>
        <BeforeShow Fn="MultiSelect_ContextMenu_BeforeShow"></BeforeShow>
    </Listeners>
</ext:Menu>

I wanna get MultiSelect Item , wherever the user right click on MultiSelect , Then if there isn't any item at MultiSelect, I wanna disable MenuItem_Delete else I wanna get the MultiSelect Item ID, with JavaScript
Could you please guide me, How I can do it in JavaScript?

Thanks