I'm trying to accomplish tracking an event when a user leaves the page with Google Analytics (analytics.js). Though it is unknown how the user will leave, it may be because of an external link or just closing the tab. So my thought was to hook onto the beforeunload or unload event and then:

window.addEventListener(beforeunload, function() {

    ga('send', 'event', 'some', 'other', 'data');

});

Now my question is, will the request to the GA server be synchronous or can I somehow force that behaviour with the hitCallback property? If that is not possible, how else can I achieve this? Preferably without having to set a timeout or fixed waiting time for the user!