This recursive function uploads chunks to a file in a document library

Step7-LargeFileUpload-UploadChunk.js

//the final REST call is made to get the file information after it has been fully uploaded (especially the file list item id)
function getFileInformation(libraryPath, fileName, resolve, reject) {
  let endpoint = String.format("{0}/_api/sp.appcontextsite(@target)/web/getfilebyserverrelativeurl(@libraryPath)/ListItemAllFields?@target='{3}'&@libraryPath='/sites/assetdatabase/{1}/{2}'",
        utils.getSpContaxtUrlParams().appWebUrl, libraryPath, fileName, utils.getSpContaxtUrlParams().hostWebUrl);

  const headers = {
    "Accept": "application/json; odata=verbose"
  };

  executeAsync(endpoint, '', headers).then(fileListItem => {
    console.log('fetching file information');

    const items = fileListItem.body ? fileListItem.body : fileListItem;
    const listItem = JSON.parse(items);

    //..and we are done.
    resolve(listItem.d);
  }).catch(err => {
    reject(err.responseText);
  });
}

function uploadFile(result, id, libraryPath, fileName, chunks, index, byteOffset, chunkPercentage, resolve, reject) {
  //we slice the file blob into the chunk we need to send in this request (byteOffset tells us the start position)
  const data = convertFileToBlobChunks(result, byteOffset, chunks[index]);

  if (byteOffset === 0) {
    //at the beginning of the upload set the message and starting percentage (0%)
    setLoaderMessage(true, 0);
  }

  //upload the chunk to the server using REST, using the unique upload guid as the identifier
  uploadFileChunk(id, libraryPath, fileName, chunks[index], data, byteOffset).then(
    value => {
        const isFinished = index === chunks.length - 1;

        if (!isFinished) {
          //the response value is a string of JSON (ugly) which we need to consume to find the offset
          const response = typeof value.body !== 'undefined' ? JSON.parse(value.body) : '';

          //depending on the position in the upload, the response string (JSON) can differ!
          if (typeof response.d.StartUpload !== 'undefined') {
            byteOffset = Number.parseInvariant(response.d.StartUpload);
          } else if (typeof response.d.ContinueUpload !== 'undefined') {
            byteOffset = Number.parseInvariant(response.d.ContinueUpload);
          }
        }

        index += 1;

        const percentageComplete = isFinished ? 100 : Math.round((index * chunkPercentage));
        // progress indication
        setLoaderMessage(true, percentageComplete);
        console.log(percentageComplete + '%');

        //More chunks to process before the file is finished, continue
        if (index < chunks.length) {
          uploadFile(result, id, libraryPath, fileName, chunks, index, byteOffset, chunkPercentage, resolve, reject);
        } else {
          setLoaderMessage(false);

          //check in the file and then resolve the file information back to the caller  
          //checkinMajorVersion(libraryPath, fileName).then(() => {
            //when there was a checkin needed
            getFileInformation(libraryPath, fileName, resolve, reject);
          //}).catch(err => {
            //no checkin was necessary
            //getFileInformation(libraryPath, fileName, resolve, reject);
          //});
        }
      }
  ).catch(err => { console.log('Error in uploadFileChunk! '); window.Erz = err; });
}