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
[解决办法]

setTimeout(ChangeBG(),1000);

function ChangeBG(){

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

}