We had similar experiences with boomerang when we first implemented sendBeacon (I think about 3 years ago). You can see our solution here: <a href="https://github.com/akamai/boomerang/blob/master/boomerang.js#L3823-L3847" rel="nofollow">https://github.com/akamai/boomerang/blob/master/boomerang.js...</a>