#### 用户头像
点击上传用户头像,并使用 `beforeUpload` 限制用户上传的图片格式和大小。
`beforeUpload` 的返回值可以是一个 Promise 以支持异步处理,如服务端校验等
#### Avatar
Click to upload user's avatar, and validate size and format of picture with `beforeUpload`.
The return value of function `beforeUpload` can be a Promise to check asynchronously.
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