Most probably they're using the sendBeacon method triggered by the visibilitychange event. sendBeacon doesn't delay the unload and asynchronously makes the netw

Most probably they're using the sendBeacon method triggered by the visibilitychange event. sendBeacon doesn't delay the unload and asynchronously makes the network request simultaneously. https://developer.mozilla.org/en-US/docs/Web/API/Navigator/sendBeacon https://developer.mozilla.org/en-US/docs/Web/API/Navigator/s...