WebSocket vs Server-Sent Events vs polling — when would you use each?

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"We need real-time notifications. WebSocket seems overkill for one-way updates. What are the options?"

Interview OS Community · Accepted Answer

| Feature | WebSocket | SSE | Polling |
|---------|-----------|-----|---------|
| Direction | Bidirectional | Server → Client | Client → Server |
| Connection | Persistent | Persistent | New per request |
| Latency | ~ms | ~ms | Seconds |
| Complexity | Medium | Low | Lowest |
| Reconnection | Manual | Auto | N/A |
| Best for | Chat, gaming | Notifications, feeds | Rare updates |

**For notifications**: SSE is perfect. Simple HTTP, auto-reconnect, no WebSocket complexity.
```typescript
// Server: SSE
return new Response(new ReadableStream({ start(ctrl) { ctrl.enqueue(`data: ${JSON.stringify(notification)}`
`); } }), { headers: { "Content-Type": "text/event-stream" } });
```

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WebSocket vs Server-Sent Events vs polling — when would you use each?

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