s3.js

const s3Client = ({ bucket }) => {
  // If the bucket is a "directory bucket" then we need to
  // use a custom endpoint via the availability zone.
  // See https://docs.aws.amazon.com/AmazonS3/latest/userguide/directory-bucket-naming-rules.html
  if (bucket.endsWith('--x-s3')) {
    const bucketAndAzid = bucket.slice(0, -6);
    const parts = bucketAndAzid.split('--');
    const azid = parts[parts.length - 1];
    // See https://docs.aws.amazon.com/AmazonS3/latest/userguide/s3-express-Regions-and-Zones.html
    const customEndpoint = `https://s3express-${azid}.${region}.amazonaws.com`;
    return new AWS.S3({
      endpoint: customEndpoint,
    });
  }

  return s3;
};