A browser application must verify that its server-side business loop is responsive. Which…

A browser application must verify that its server-side business loop is responsive. Which heartbeat is appropriate?

1. Call `socket.ping()` from browser JavaScript.
2. Send an application heartbeat with a sequence or time and enforce a bounded reply timeout.
3. Treat any `bufferedAmount` value as proof that the server is alive.
4. Reconnect continuously until one attempt succeeds.