i wants to call form action attribute after executing onclick event in a button.How can we do that task

In aspx page

<script type="text/javascript" language="javascript">

    function sendMail() {
        document.getElementById('form1').action = "http://sitename/modules/Webforms/capture.php";
        document.getElementById('form1').method = "post";
        form1.submit();
    }


</script></script>

In .cs page
protected void btnsubmit_click(object sender, EventArgs e)
{
Page.ClientScript.RegisterStartupScript(this.GetType(), "ResizeRadWindow", "<script type='text/javascript'> sendMail(); </script>");
}