base64图片转为可上传的file

    base64toFile(dataUrl, fileName) {
      const arr = dataUrl.split(',')
      const mime = arr[0].match(/:(.*?);/)[1]

      const bstr = window.atob(arr[1]) // base64编码
      let n = bstr.length
      const u8arr = new Uint8Array(n)
      while (n--) {
        u8arr[n] = bstr.charCodeAt(n) // unicode 编码
      }
      return new File([u8arr], `${fileName}.png`, {
        type: mime
      })
    },