H5：上传图片

// base64转文件流
base64toFile(dataurl, filename = new Date().valueOf()) {
  const arr = dataurl.split(',')
  const mime = arr[0].match(/:(.*?);/)[1]
  const suffix = mime.split('/')[1]
  const bstr = atob(arr[1])
  let n = bstr.length
  const u8arr = new Uint8Array(n)
  while (n--) {
  u8arr[n] = bstr.charCodeAt(n)
  }
  return new File([u8arr], `${filename}.${suffix}`, {
      type: mime
  })
}

// 注意：上传图片要用post请求，并且将header设置为 'Content-Type': 'multipart/form-data'
async excuteUploadImage() {
  const fileField = `data:image/png;base64,${photoStr}`
  const form = new FormData()
  form.append('file', this.base64toFile(fileField))
  const photoRes = await uploadFile(form)
}