mediumSystem Design

When would you use WebSockets vs polling vs SSE?

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01

Understand the problem

Compare real-time techniques.

realtimewebsockets
02

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03

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04

Read the code

WebSocket vs SSE client
// WebSocket: full-duplex — both sides can send any time.
const ws = new WebSocket('wss://example.com/chat');
ws.onopen    = () => ws.send(JSON.stringify({ type: 'join', room: 'general' }));
ws.onmessage = (e) => console.log('received', e.data);

// SSE: server -> client only, auto-reconnects; you just listen.
const es = new EventSource('/api/stream');
es.onmessage = (e) => console.log('event', e.data);
05

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