Refresh UpdatePanel on postback, using JavaScript in Asp.net

in .aspx page

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

<div id="Container" onclick="__doPostBack('UpdatePanel1', '');">

<asp:UpdatePanel runat="server" ID="UpdatePanel1" 
    OnLoad="UpdatePanel1_Load">
  <ContentTemplate>
    <asp:Label runat="server" ID="Label1" />
  </ContentTemplate>
</asp:UpdatePanel>

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

        <asp:Label runat="server" ID="Label2" />

in .cs page

protected void UpdatePanel1_Load(object sender, EventArgs e)
{
  Label1.Text = DateTime.Now.ToString();
}


protected void Button1_Click(object sender,EventArgs e)
{
   Label2.Text = DateTime.Now.ToString();

}




output


On Button click updatepanel get postback first
(display Label1.Text first) on second time Click (Label2.Text value get display)