Js input type=file 的学习

https://www.liaoxuefeng.com/wiki/1022910821149312/1023022494381696  //引入

https://developer.mozilla.org/zh-CN/docs/Web/HTML/Element/Input/file  //细节讲解文档

https://www.haorooms.com/post/input_file_leixing   //常用MIME类型

https://www.w3school.com.cn/tags/att_label_for.asp  //label 的for 绑定

https://www.cnblogs.com/fozero/p/8835628.html  //实例

https://www.jianshu.com/p/134473c8d162  //实例