将控件动态添加到ASP.NET AJAX中的UpdatePanel

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
   <ContentTemplate>
        <asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>
    </ContentTemplate>
</asp:UpdatePanel>

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        TextBox txtBox = new TextBox();
        txtBox.ID = "TextBox1";
        txtBox.Text = "Hello, World!";
        PlaceHolder1.Controls.Add(txtBox);
    }
}

function addControl() {
    var updatePanel = document.getElementById("<%= UpdatePanel1.ClientID %>");
    var placeholder = document.getElementById("<%= PlaceHolder1.ClientID %>");
    var txtBox = document.createElement("input");
    txtBox.type = "text";
    txtBox.id = "TextBox1";
    txtBox.value = "Hello, World!";
    placeholder.appendChild(txtBox);
    __doPostBack('<%= UpdatePanel1.ClientID %>', '');
}