<form action="" method="post">
     <input type="button" onclick="metho()">
</form>

<script type="text/javascript">
function metho() {
        var dForm = document.getElementById("dForm");
        dForm.action = "process.do";
        dForm.submit();
    }
</script>

<form action="" method="post" id="dForm>
     <input type="button" onclick="metho()">
</form>

------解决方案--------------------
HTML code
<script type="text/javascript">
function metho() {
        var dForm = documentforms[0];
        dForm.action = "url";
        dForm.submit();
    }
</script>

<form action="" method="post">
     <input type="button" onclick="metho()">
</form>

------解决方案--------------------
<script type="text/javascript">
function metho() {
       var dForm = document.getElementById("dForm");
       dForm.action = "process.do";
       dForm.submit();
   }
</script>

<form action="" method="post" id="dForm>
    <input type="button" onclick="metho()">
</form>



-->等价于

<form action="process.do" method="post" id="dForm>
    <input type="submit"   />
</form>

上面的绕道到js里面提交到process.do