动态设置默认按钮

<script type="text/javascript">     document.onkeydown=xx;     function xx()     {         var se = event.srcElement;         if(event.keyCode==13)         {              if(se.id=="textBox1")             {             document.getElementById("button1").focus();             document.getElementById("button1").click();             }             if(se.id=="textBox2")             {              document.getElementById("button2").focus();              document.getElementById("button2").click();             }         }     }    </script>

<form id="form1" runat="server">        <div>            <table width="100%" cellpadding="2" cellspacing="2" border="1">                <tr>                    <td>                        <asp:TextBox ID="textBox1" runat="server"></asp:TextBox></td>                    <td>                        <asp:TextBox ID="textBox2" runat="server"></asp:TextBox></td>                </tr>                <tr>                    <td>                        <asp:Button ID="button1" runat="server" Text="button1" OnClick="button1_Click"></asp:Button></td>                    <td>                        <asp:Button ID="button2" runat="server" Text="button2" OnClick="button2_Click"></asp:Button></td>                </tr>            </table>        </div>    </form>