How do you implement real-time features with WebSockets in Node.js?

Question

Accepted Answer

**WebSockets** — persistent bidirectional connection between client and server.

**Using ws library:**
```javascript
const { WebSocketServer } = require("ws");
const http = require("http");

const server = http.createServer();
const wss = new WebSocketServer({ server });

wss.on("connection", (ws, req) => {
    console.log("Client connected");

ws.on("message", (data) => {
        const message = JSON.parse(data);
        // Broadcast to all clients
        wss.clients.forEach((client) => {
            if (client.readyState === WebSocket.OPEN) {
                client.send(JSON.stringify(message));
            }
        });
    });

ws.on("close", () => console.log("Client disconnected"));
    ws.send(JSON.stringify({ type: "welcome" }));
});

server.listen(8080);
```

**Using Socket.IO (higher level):**
```javascript
const { Server } = require("socket.io");
const io = new Server(server);

io.on("connection", (socket) => {
    socket.join("room1");
    socket.to("room1").emit("message", "hello");
    socket.on("disconnect", () => {});
});
```

**Key points:**
- ws is lightweight; Socket.IO adds rooms, reconnection.
- Handle binary data for performance.
- Use heartbeat/ping to detect stale connections.

Node.js: How do you implement real-time features with WebSockets in Node.js?