文件大小转换

convertBytesToSize(bytes) {
  const thresh = 1024;
  if (Math.abs(bytes) < thresh) {
    return bytes + ' B';
  }
  const units = ['KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
  let u = -1;
  do {
    bytes /= thresh;
    ++u;
  } while (Math.abs(bytes) >= thresh && u < units.length - 1);
  return bytes.toFixed(1) + ' ' + units[u];
}