<asp:Label ID="Lbl_X" runat="server" Text="text" style="display:none"></asp:Label>
<asp:Label ID="Lbl_Xn" runat="server" Text="text" style="display:none"></asp:Label>
JS:
  <%-- 設置選中--%>
    <script type="text/javascript">
        var X = document.getElementById('<%=this.Lbl_X.ClientID %>').innerText;
        var Xn = document.getElementById('<%=this.Lbl_Xn.ClientID %>').innerText;
        var div = document.getElementById(X);
        if (div != null) {
            div.setAttribute("class", 'nav-top-item current');
        }
        var div2 = document.getElementById(Xn);
        if (div != null) {
            div2.setAttribute("class", 'current');
        }
    </script>
   

            Label X = (Label)this.Master.FindControl("Lbl_X");
            X.Text = "A";
            Label Xn = (Label)this.Master.FindControl("Lbl_Xn");
            Xn.Text = "A1";