JavaScript SDK does not return thumbnails

1. The filesGetThumbnail (and any other method that returns data in the response) makes the data available in the response's fileBlob property, if you're running in the browser, and fileBinary if you're running in node.

So, for example, you can do this:

dbx.filesGetThumbnail({path: remoteFilePath})
  .then(function(response) {
    console.log(response);
    console.log(response.rev);
    console.log(response.fileBlob);

    // do whatever you want with the data here, e.g.:
    objectURL = URL.createObjectURL(response.fileBlob)
    var downloadButton = document.createElement('a');
    downloadButton.setAttribute('href', objectURL);
    downloadButton.setAttribute('download', response.name);
    downloadButton.setAttribute('class', 'button');
    downloadButton.innerText = 'Download: ' + response.name;
    document.getElementById('results').appendChild(downloadButton);
  })
  .catch(function(error) {
    console.error(error);
  });

2. I covered this a bit in your other thread, but you should use the native properties on the response project. The code example above access the "rev", for instance.