XMLHttpRequest on main thread is deprecated

[Jos512]

If I perform a Google mobile friendly test on a website that uses ga-lite, I get the following error message:

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

Here's an example of such a mobile friendliness report.

The problem looks to be caused by this line.

[jehna]

Hmm. This tracks down to the very first commit:

ga-lite/src/ga-lite.js

Lines 21 to 22 in 719d3c7

	req.open('GET', url, false);
	req.send();

Back then ga-lite had functionality of sending the pageviews on window.onunload, and since Internet Explorer doesn't support navigator.sendBeacon, there was a fallback to use XMLHttpRequest. The gist here is that IE needed to use synchronous requests to guarantee taht those requests were finished on the unload event.

This means we can safely remove the synchronous flag from the XMLHttpRequest call.

[jehna]

Source and further explanation for the synchronous flag:

https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Synchronous_and_Asynchronous_Requests#Adapting_Sync_XHR_usecases_to_the_Beacon_API