Ajax表单以cshtml提交

Question

I'm using this form for ajax submission:

<form class="status-form" role="form" action="" enctype="multipart/form-data" id="statusupdateform" method="post">

And this javascript to do the ajax functions:

<script type="text/javascript">
    var frm = $('#statusupdateform');
    frm.submit(function (ev) {
        $.ajax({
            type: frm.attr('method'),
            url: frm.attr('action'),
            data: frm.serialize(),
            success: function (data) {
                alert('ok');
            }
        });
        ev.preventDefault();
    });
</script>

But actually it refreshes the whole page.

How can I do this?