Compare Polling vs Long Polling vs WebSockets vs Server-Sent Events (SSE) for real-time UIs.
❓ Interview Prompt: Compare real-time communication protocols: Short Polling, Long Polling, WebSockets (full-duplex TCP), and Server-Sent Events (SSE HTTP streaming).
Evaluating real-time client-server communication technologies:
| Technology | Direction | Protocol | Ideal Use Case |
|---|---|---|---|
| Short Polling | Client $\rightarrow$ Server | HTTP | Low-frequency periodic updates |
| Long Polling | Client $\leftrightarrow$ Server | HTTP (Kept open) | Legacy push updates without WebSocket support |
| WebSockets | Bi-directional (Full-Duplex) | TCP ('ws://' / 'wss://') | Real-time chat, multiplayer gaming, collaborative editing |
| Server-Sent Events (SSE) | Server $\rightarrow$ Client (Uni-directional) | HTTP ('text/event-stream') | Live stock tickers, news feeds, LLM token streaming |
Code Implementation Example
// Client-side Server-Sent Events (SSE) listener
const eventSource = new EventSource('/api/v1/live-stock-stream');
eventSource.onmessage = (event) => {
const data = JSON.parse(event.data);
console.log('Real-time price update:', data);
};Use WebSockets for bi-directional real-time communication (chat), and SSE for uni-directional server streaming (stock tickers, LLMs).