Algorithm for creating a multipart upload to AWS S3

multipartUpload.ts

const { UploadId: uploadId } = await s3
    .createMultipartUpload({
      Bucket: `${process.env.BUCKET_NAME}`,
      Key: key,
    })
    .promise()

  async function uploadPart(
    partNumber: number,
    uploadId: string,
    body: Buffer
  ) {
    const partParams: S3.UploadPartRequest = {
      Bucket: `${process.env.BUCKET_NAME}`,
      Key: key,
      UploadId: `${uploadId}`,
      PartNumber: partNumber,
      Body: body,
    }

    const uploadedPart = await s3.uploadPart(partParams).promise()

    return {
      ETag: uploadedPart.ETag,
      PartNumber: partNumber,
    }
  }

  const promisedParts = []

  for (let progress = 0; progress < body.length; progress += partSize) {
    const partNumber = progress / partSize + 1

    const promisedPart = uploadPart(partNumber, String(uploadId), body)

    promisedParts.push(promisedPart)
  }

  const parts = await Promise.all(promisedParts)

  const result = await s3
    .completeMultipartUpload({
      Bucket: `${process.env.BUCKET_NAME}`,
      Key: key,
      UploadId: `${uploadId}`,
      MultipartUpload: {
        Parts: parts,
      },
    })
    .promise()