Working with Ping and Pong Frames

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

wss.on("connection", (c) => {
  c.isAlive = true;
  c.on("pong", () => { c.isAlive = true; });
});

let hb;
ws.addEventListener("open", () => {
  hb = setInterval(() => ws.send(JSON.stringify({ "type": "ping" })), 25000);
});
ws.addEventListener("close", () => clearInterval(hb));

if (c.isAlive === false) c.terminate(); // skip close handshake

const sent = new Map();
function ping() {
  const id = crypto.randomUUID();
  sent.set(id, performance.now());
  ws.send(JSON.stringify({ "type": "ping", "id": id }));
}
function onPong({ id }) {
  const rtt = performance.now() - sent.get(id);
  sent.delete(id);
  metrics.observe("rtt_ms", rtt);
}