How to get getElementById

<div id ="SubMenu<%# DataBinder.Eval(Container, "ItemIndex")%><%# DataBinder.Eval(Container.DataItem, "DescriptionMenu")%>" style="display:none;" ><asp:Repeater id="rptSubMenu" runat="server" OnItemCommand="rptSubMenu_ItemCommand" ><ItemTemplate><asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate><asp:LinkButton ID="lnkSubMenu" CommandName="ShowEvents" CommandArgument='<%# Eval("Url")%>' runat="server" Text='<%# Eval("SubMenu")%>' ></asp:LinkButton><%--<asp:HiddenField ID="hdfEventID" Value='<%# Eval("Url")%>' runat="server" />--%></ContentTemplate></asp:UpdatePanel></ItemTemplate></asp:Repeater></div>

      function setState2(pageID) {
          var div;
          var i = 0;

          while (div = document.getElementById('SubMenu' + (i++)))
              setDisplay(div, GetCookie(div.id + ':' + pageID));
      }    

This is not works. How to get <div id ="SubMenu<%# DataBinder.Eval(Container, "ItemIndex")%><%# DataBinder.Eval(Container.DataItem, "DescriptionMenu")%>" with javascript:

while (div = document.getElementById('SubMenu' + (i++)))

I need to get element DataBinder.Eval(Container.DataItem, "DescriptionMenu") here: while (div = document.getElementById('SubMenu' + (i++)))

Please help