Why is ProgressEvent.lengthComputable false?

Question

I am loading a JSON file using XMLHttpRequest in Google Chrome, Safari and Firefox. In all three browsers I am receiving ProgressEvents which correctly show the

Answer 1

If lengthComputable is false within the XMLHttpRequestProgressEvent, that means the server never sent a Content-Length header in the response.

If you're using nginx as a proxy server, this might be the culprit, especially if it's not passing the Content-Length header from the upstream server through the proxy server to the browser.