The Classic Fallback

Long Polling is the oldest method to simulate " real-time " updates. It's still used as a fallback when WebSockets and SSE are blocked (e.g., by strict corporate firewalls).

How It Works

1. Browser sends a request to the server.
2. Server does NOT respond immediately — it holds the connection open until it has new data.
3. When new data arrives, the server responds.
4. Browser receives the response and immediately sends a new request.
5. Repeat.

async function subscribe() {
  try {
    const response = await fetch('/api/subscribe', {
      signal: AbortSignal.timeout(30_000) // 30 second timeout
    });

    if (response.status === 200) {
      const message = await response.json();
      handleNewMessage(message);
    }
  } catch (error) {
    if (error.name !== 'TimeoutError') {
      // Real error — wait before retrying
      await new Promise(resolve => setTimeout(resolve, 2000));
    }
  }
  
  // Always schedule next poll
  subscribe();
}

subscribe(); // Start the loop