How do you build an efficient WebSocket server with the ws library and implement a Heartbeat (Ping/Pong)?

Short answer

An HTTP connection is upgraded to a bidirectional socket, and periodic Ping messages check that the connection is alive and close dead sockets (Zombie Connections).

Explanation

WebSocket connections begin with a regular HTTP request containing the Upgrade: websocket header. After the upgrade, the connection becomes a bidirectional TCP stream. Because a sudden client disconnection (such as Wi-Fi being turned off) may not send a TCP FIN packet, the server should send Ping messages every 30 seconds; if the client does not reply with Pong, treat the connection as dead and call socket.terminate() to release resources.

Code example

import { WebSocketServer } from "ws";
const wss = new WebSocketServer({ port: 8080 });
setInterval(() => {
  wss.clients.forEach(ws => {
    if (!ws.isAlive) return ws.terminate();
    ws.isAlive = false;
    ws.ping();
  });
}, 30000);

Common mistakes

• Skipping Ping/Pong, which can leave thousands of dead sockets open on the server and consume memory.

Follow-up questions

• When should you prefer Server-Sent Events (SSE) over WebSockets, and how do you implement SSE in Node.js?

Sources

• MDN — The WebSocket API
• Node.js docs — http: Event 'upgrade'