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

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.

// Server: SSE
return new Response(new ReadableStream({ start(ctrl) { ctrl.enqueue(`data: ${JSON.stringify(notification)}`
`); } }), { headers: { "Content-Type": "text/event-stream" } });