用的layui的上傳控件，為什么傳到后臺之后是null?。?/h1>

html

<div class="layui-upload biangeng_3_1">
                <button type="button" class="layui-btn" id="yingyezhizhao"><i class="layui-icon">&#xe67c;</i>營業(yè)執(zhí)照</button>
                <div class="layui-upload-list">
                    <img class="layui-upload-img" id="yingyezhizhao_preview">
                   <!-- <p id="demoText"></p>-->
                </div>
            </div>

js

layui.use('upload', function(){
    var upload = layui.upload;

    //執(zhí)行實例
    var uploadInst = upload.render({
        elem: '#yingyezhizhao' //綁定元素
        ,url: '../app/upload/changeImg' //上傳接口

        ,done: function(res){
            //上傳完畢回調(diào)
            $('#yingyezhizhao_preview').attr('src','../'+ data.data);
            layer.msg('上傳成功！');
        }
        ,error: function(){
            layer.msg('上傳失敗');
        }
    });
});