WebSocket: пример кода

// Production-grade client: reconnect with backoff, heartbeat, and cleanup
function connect() {
  const ws = new WebSocket('wss://api.example.com/ws');
  let heartbeat;

  ws.onopen = () => {
    ws.send(JSON.stringify({ type: 'auth', token })); // can't set headers → auth in-band
    // Heartbeat: prove the connection is alive; a missing pong means it's dead
    heartbeat = setInterval(() => {
      if (ws.readyState === WebSocket.OPEN) ws.send(JSON.stringify({ type: 'ping' }));
    }, 30_000);
  };

  ws.onmessage = (e) => handle(JSON.parse(e.data));

  ws.onclose = () => {
    clearInterval(heartbeat);
    // ❌ `setTimeout(connect, 1000)` → every client retries in lockstep = thundering herd
    // ✅ exponential backoff + jitter spreads the reconnect storm
    const delay = Math.min(1000 * 2 ** attempt, 30_000) * (0.5 + Math.random());
    setTimeout(connect, delay);
    attempt++;
  };

  ws.onerror = () => ws.close(); // let onclose own the reconnect logic (one path)
}

// Backpressure: don't blindly push — a slow client's buffer will blow up memory
if (ws.bufferedAmount < 1_000_000) ws.send(payload); // else drop/throttle/coalesce