FYI Haven't tested the code but browser compatibility looks pretty good now:

After reading the doc of sendBeacon it looks like the ideal solution for what we're doing! this should resolve some of the web server errors (at least on apache)

@mattab I tested it again and also checked in the logs and it worked.

There is one thing that is a bit annoying but it always has been like this already: I noticed sometimes 2 POST requests. Eg a user submits a form, a POST request is sent, a few ms later the "unload" event occurs and the browser cancels these requests, then we retry them and send the second request. In the callback where we usually fallback to get request, we cannot know if the initial POST was already successfully transferred to the server or not (eg maybe request completed but response wasn't sent yet) and in the worst case this could cause the same data to be tracked twice. This affects all POST requests that are made shortly before unload. I wonder if we should always execute such requests with like a 50ms timeout for example?

In my tests this prevent this problem like this:

                if (isPageUnloading && sendPostRequestViaSendBeacon(request)) {
                    return;
                }

                setTimeout(function () {
                    if (isPageUnloading && sendPostRequestViaSendBeacon(request)) {
   // meanwhile maybe the unload event occured
                        return;
                    }
                    sendRequestTheRegularPostWay();
                }, 50);

FYI: I believe this timeout I just explained is the way to go and helpful... therefore pushed the change.

Great find with the new setTimeout and 50 ms which will help track more accurate data 👍