base64 图片计算大小 bytes

const base64toBlob = (dataURI: string) => {
  try {
    const matches = dataURI.match(/data:(.+);/);
    if (!matches || matches.length < 1) return null;
    const imgType = matches[1];
    const byteString = atob(dataURI.split(',')[1]);
    const ab = new ArrayBuffer(byteString.length);
    const ia = new Uint8Array(ab);
    for (let i = 0; i < byteString.length; i++) {
      ia[i] = byteString.charCodeAt(i);
    }
    return new Blob([ab], { type: imgType });
  } catch (e) {
    return null;
  }
};