http://www.ruanyifeng.com/blog/2012/09/xmlhttprequest_level_2.html

http://www.cnblogs.com/yuanlong1012/p/5127497.html

https://front-js.cc/test/fileupload/

http://www.ruanyifeng.com/blog/2012/08/file_upload.html

Js上传进度条