Creating asp.net textbox using javascript ?

<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
    <script src="Scripts/jquery-1.4.1.js" type="text/javascript"></script>
    <script type="text/javascript">
            function createtextbox() {
                var txt = "<input id='txt1' type='text'>";
                txt += "</input>";
                $("#MainContent_txtcontainer").append(txt);
            }
    </script>
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
    <div id="txtcontainer"  runat="server">
        <input id="asa" type="button" value="add" onclick="createtextbox();"  />
        <asp:Button ID="Button1" runat="server" Text="Button" />
    </div>
</asp:Content>