Concurrent Upload of Large Files in JavaScript

upload.js

function upload({
  url,
  file,
  fileMd5,
  fileSize,
  chunkSize,
  chunkIds,
  poolLimit = 1,
}) {
  const chunks =
    typeof chunkSize === "number" ? Math.ceil(fileSize / chunkSize) : 1;
  return asyncPool(poolLimit, [...new Array(chunks).keys()], (i) => {
    if (chunkIds.indexOf(i + "") !== -1) {
      // Ignore uploaded chunks
      return Promise.resolve();
    }
    let start = i * chunkSize;
    let end = i + 1 == chunks ? fileSize : (i + 1) * chunkSize;
    const chunk = file.slice(start, end);
    return uploadChunk({
      url,
      chunk,
      chunkIndex: i,
      fileMd5,
      fileName: file.name,
    });
  });
}