IE8 browser Webloader will always go uploaderror and report error: http

When using Baidu webloader, the IE8 browser will always use the uploaderror when debugging

uploader.on( 'uploadError', function( file,reason ) {
     alert(reason) ;
});

The reason error is http. The reason is:
the reason why JSON is returned when it is returned in the background.

The backend of webuploader cannot return json, convert json to string type, take com.alibaba.fastjson.JSONObject as an example,
com.alibaba.fastjson.JSONObject.toJSONString([json or object data]);