form表单提交时用JavaScript跳转，action怎么带参数

<script type="text/javascript">
function selflog_show()
{
var num =  document.getElementById("number").value;
var id =  document.getElementById("id").value;
var r=confirm("添加进购物车成功！");
var form1=document.getElementsByTagName("form")[0];
form1.action=form1.action+"?id="+id+"&num="+num;

}
function add()
{
var num = parseInt(document.getElementById("number").value);
if(num<100)
{
document.getElementById("number").value = ++num;
}
}
function sub()
{
var num = parseInt(document.getElementById("number").value);
if(num>1)
{
document.getElementById("number").value = --num;
}
}

</script>

<input type="button" name="less" id="sub" value="-" onclick="sub();">
<input type="text" name="number" id="number" value="1" size="2">
<input type="button" name="more" id="add" value="+" onclick="add();"><br><br>
<s:form action="cartAction_addGoodsIntoCart" id="form1" method="post">
<input type="image" src="./pictures/cart.png" onclick="selflog_show();">
</s:form>

<s:hidden name="id" value="%{model.itemsid}" />