Q118- Difference between Websocket and Long Polling

Both WebSocket and Long Polling are techniques to achieve real-time communication between a client and server, but they work differently in performance, connection style, and efficiency.

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1️⃣ WebSocket

• Definition: WebSocket provides a full-duplex, persistent connection between client and server.
• How it works:
  1. Client sends a WebSocket handshake request
  2. Server upgrades HTTP connection to WebSocket
  3. Both client and server can send messages anytime
• Use Cases: Chat apps, live notifications, real-time dashboards

Example:

// Client
const socket = new WebSocket("ws://localhost:8080");

socket.onopen = () => socket.send("Hello Server!");
socket.onmessage = (msg) => console.log("Server says:", msg.data);

Pros:

• Low latency and bi-directional communication
• Efficient for frequent messages
• Less overhead after connection is established

Cons:

• Slightly more complex to implement
• Requires persistent connection, may not scale easily without proper infrastructure

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2️⃣ Long Polling

• Definition: Long polling uses HTTP requests to simulate real-time updates. The client keeps requesting the server, and the server holds the request until new data is available.
• How it works:
  1. Client sends HTTP request
  2. Server waits until data is available or timeout occurs
  3. Server responds → client immediately sends another request

Example:

async function longPoll() {
  const response = await fetch("/api/updates");
  const data = await response.json();
  console.log(data);
  longPoll(); // immediately start next poll
}

longPoll();

Pros:

• Works over standard HTTP (no WebSocket support needed)
• Easy to implement on existing HTTP infrastructure

Cons:

• Higher latency compared to WebSocket
• More network overhead (each request carries headers)
• Can stress the server if many clients are polling

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3️⃣ Key Differences

Feature	WebSocket	Long Polling
Connection	Persistent, full-duplex	Short-lived HTTP requests
Communication	Bi-directional	Client → Server request only
Latency	Low, near real-time	Higher, depends on server delay
Network Overhead	Low after handshake	High (repeated HTTP requests)
Use Case	Chat, live dashboards, games	Notifications, legacy systems
Server Load	Moderate	High with many clients

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⚡ In short:

WebSocket is best for real-time, high-frequency bi-directional communication, while Long Polling is simpler but less efficient, suitable for occasional updates or legacy systems.