XHR

```
const xhr = new XMLHttpRequest();
xhr.open("POST", url, true);
xhr.onreadystatechange = () => {
 if (xhr.readyState === 4) {
  if (xhr.status === 200) {
   console.log("成功");
  } else {
   console.log("上传失败", xhr);
  }
 }
};
xhr.setRequestHeader("Content-type", file.type);
xhr.send(file);
```

https://www.jianshu.com/p/918c63045bc3
https://www.cnblogs.com/52fhy/p/5436673.html