如何用javascript给form增加一个控件？

Question

<script language="javascript">function aa()
{
try
{
var oForm = document.all("ff");
var oInput = document.createElement("INPUT");
oInput.setAttribute("type","hidden");
oInput.setAttribute("id","aaa");
oForm.appendChild(oInput);
document.all("aaa").value = "ggg";
alert(document.all("aaa").value);
}
catch(e)
{
alert(e.description);
}
}</script>
<form name="ff">
<input type="button" onclick="aa()" value="插入input">
</form>

Answer 1

formname.insertAdjancentHTML("BeforeEnd","<input type=hidden name=n value=s")

Answer 2

<script>
function inner(){
document.all('test').innerHTML="<input type=hidden>"
}
</script>
<form id=zfl>
<span id=test></span>
<input type=button value=inner onclick="inner()">
</form>