corsEnabled uses deprecated synchronous xhr

[zxubian]

Starting in Firefox 30, synchronous requests on the main thread have been deprecated due to their negative impact on performance and the user experience. Therefore, the async parameter may not be false except in a Worker.

https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/open

From FileSaver.js:

function corsEnabled (url, opts) {
  var xhr = new XMLHttpRequest()
  // use sync to avoid popup blocker
  xhr.open('HEAD', url, false)
  try {
    xhr.send()
  } catch (e) {}
  return xhr.status >= 200 && xhr.status <= 299
}

[alekstar79]

Yes, Chrome also swears on Synchronous XMLHttpRequest.

[Deprecation] Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.

[priley86]

Will passing xhr.open('HEAD', url, true) fix the issue? It may be worth forking this package...

[igneosaur]

Yeh, using xhr.open('HEAD', url); does fix the issue. However it does seem like the synchronous event was used deliberately to avoid popup blockers.

[igneosaur]

I guess there won't be a choice soon.