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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

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

Nudge consolestandby

Stuck? Beam a request up — the console returns a conceptual nudge that guides your logic without spoiling the implementation.

03

Study the solution

Step 1: Outline use cases and constraints

Gather requirements and scope the problem. Ask questions to clarify use cases and constraints. Discuss assumptions.

Use cases

We'll scope the problem to handle only the following use cases

  • User needs to understand realtime to make architecture decision

Solution ready — 2 min read

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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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