The returned value cannot be obtained correctly when a file is uploaded using ajaxfileupload.

At the beginning, I didn't feel the importance of the datatype parameter of the Ajax request. After using the ajaxfileupload plug-in, if the Page code is as follows:

Fileelementid: ['imagetoupload'], URL: 'url', datatype: 'json ',

If the return type is JSON data, after the backend processes the upload, it is necessary to encapsulate the returned value into JSON format and return the data to the front-end page.

The background encapsulation is as follows:

Return "{\" Result \ ":" + "\" OK \"}";

Otherwise, the success function is not executed on the page and the error function is directly entered.