index.js

const uWS = require("uWebSockets.js");
const wss = uWS.App();

const port = process.env.PORT || 7860;

wss
  .ws("/problems/:problemId", {
    upgrade: (res, req, context) => {
      res.upgrade(
        { problemId: req.getParameter(0) },
        req.getHeader("sec-websocket-key"),
        req.getHeader("sec-websocket-protocol"),
        req.getHeader("sec-websocket-extensions"),
        context
      );
    },
    open: async (ws) => {
      const { problemId } = ws;
      ws.subscribe(problemId);
      const count = wss.numSubscribers(problemId);
      console.log(`[Join] ${problemId} - count: ${count}`);
      wss.publish(problemId, `${count}`);
    },
    close: async (ws) => {
      const { problemId } = ws;
      const count = wss.numSubscribers(problemId);
      console.log(`[Left] ${problemId} - count: ${count}`);
      wss.publish(problemId, `${count}`);
    },
  })
  .any("/*", (res, req) => {
    res.end("Nothing to see here!");
  })
  .listen('::', port, (token) => {
    if (token) {
      console.log(`Listening to port ${port}`);
    } else {
      console.log(`Failed to listen to port ${port}`);
    }
  });