使用layui问题-form表单提交时radio获取不到value值

前端页面

<form class="layui-form layui-form-pane" lay-filter="formAdd" id='formAdd'>
    <div class="layui-form-item">
        <label class="layui-form-label">类别</label>
        <div class="layui-input-block">
            <input type="radio" name="category" value="类别1" title="类别1" checked />
            <input type="radio" name="category" value="类别2" title="类别2" />
        </div>
    </div>
    <div class="layui-form-item">
        <div class="layui-input-block">
            <button class="layui-btn" lay-submit lay-filter="addform">确定添加</button>
        </div>
    </div>
</form>

JS代码

layui.use(['form'],function(){
    var form = layui.form
    , layer = layui.layer；
    form.render();
    form.on('submit(addform)', function (data) {
            $("form#formAdd input[type='radio']:checked").each(function(){
                data.field[$(this).attr('name')] = $(this).attr('title')
            });
            $.ajax({
                type: "GET",
                contentType: "application/json; charset=utf-8",
                url: '/url_str/',
                data: data.field,
                dataType: 'json',
                success: function (result) {
                    if (result.flag == 1) {
                        layer.msg("记录添加成功");
                    } else {
                        layer.alert(result.message);
                    }
                },
                error: function (XMLHttpRequest, textStatus, errorThrown) {
                    console.log(XMLHttpRequest.status);
                    console.log(XMLHttpRequest.readyState);
                    console.log(textStatus);
                }
            });
            return false;
        });
});