怎么用ajax动态设置页面背景图片
我想用ajax的timer设置当前页面的背景图片，可是不会在后台写前台的设置代码啊

protected void Page_Load(object sender, EventArgs e)

        {

            

        }

        protected void Timer1_Tick(object sender, EventArgs e)

        {

            Label1.Text = DateTime.Now.ToString();

            

        }

<form id="form1" runat="server">

    <asp:ScriptManager ID="ScriptManager1" runat="server">

    </asp:ScriptManager>

    <div id = "bg">

        <asp:Button ID="Button1" runat="server" Text="Button" />

        <asp:UpdatePanel ID="UpdatePanel1" runat="server">

        <ContentTemplate>

        <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>

            <asp:Timer ID="Timer1" runat="server" Interval="1000" OnTick="Timer1_Tick">

            </asp:Timer>

        </ContentTemplate>        

        </asp:UpdatePanel>

        

    </div>

求大神指点一二
------解决方案--------------------

setTimeout(ChangeBG(),1000);



function ChangeBG(){



document.getelementbyid("要改变背景HTML的ID").style.backgroundImage="图片路径";



}