Sample WebSocket node.js, react, express.js with broadcast and send happening in a route

App.js

import React from "react";

import { BrowserRouter as Router, Switch, Route } from "react-router-dom";
import LiveStorePurchases from "./LiveStorePurchases";

function App(props) {
  return (
    <div className="App">
      <Router>
        <Switch>
          <Route exact path="/livePurchases/:storeId">
            <LiveStorePurchases />
          </Route>
        </Switch>
      </Router>
    </div>
  );
}

export default App;

app.js

const express = require("express");
const NotifierService = require("../server/NotifierService.js");
const notifier = new NotifierService();
const http = require("http");
const routes = require("./routes");

module.exports = (config) => {
  const app = express();
  const server = http.createServer(app);
  notifier.connect(server);

  //   I moved POST /newPurchase to routes.js in order
  //   to demonstrate how the notifier instance can be
  //   passed around to different routes
  app.use(routes(notifier));

  return server;
};

LiveStorePurchases.js

import React, { useEffect, useState } from "react";
import { useParams } from "react-router-dom";

export default function LiveStorePurchases() {
  let { storeId } = useParams();
  const URL = "ws://127.0.0.1:4000?storeId=" + storeId;

  const [ws, setWs] = useState(new WebSocket(URL));

  useEffect(() => {
    ws.onopen = (e) => {
      newFunction(e);

      function newFunction(e) {
        alert("WebSocket Connected");
      }
    };

    ws.onmessage = (e) => {
      const message = e.data;
      alert(message);
    };

    return () => {
      ws.onclose = () => {
        alert("WebSocket Disconnected");
        setWs(new WebSocket(URL));
      };
    };
  }, [ws.onmessage, ws.onopen, ws.onclose, ws, URL]);

  return (
    <div
      style={{
        color: "red",
        fontSize: "4rem",
      }}
    >
      store: {storeId}
    </div>
  );
}

NotifierService.js

const url = require("url");
const { Server } = require("ws");

class NotifierService {
  constructor() {
    this.connections = new Map();
  }

  connect(server) {
    this.server = new Server({ noServer: true });
    this.interval = setInterval(this.checkAll.bind(this), 10000);
    this.server.on("close", this.close.bind(this));
    this.server.on("connection", this.add.bind(this));
    server.on("upgrade", (request, socket, head) => {
      console.log("ws upgrade");
      const id = url.parse(request.url, true).query.storeId;

      if (id) {
        this.server.handleUpgrade(request, socket, head, (ws) =>
          this.server.emit("connection", id, ws)
        );
      } else {
        socket.destroy();
      }
    });
  }

  add(id, socket) {
    console.log("ws add");
    socket.isAlive = true;
    socket.on("pong", () => (socket.isAlive = true));
    socket.on("close", this.remove.bind(this, id));
    this.connections.set(id, socket);
  }

  send(id, message) {
    console.log("ws sending message");

    const connection = this.connections.get(id);

    connection.send(JSON.stringify(message));
  }

  broadcast(message) {
    console.log("ws broadcast");
    this.connections.forEach((connection) =>
      connection.send(JSON.stringify(message))
    );
  }

  isAlive(id) {
    return !!this.connections.get(id);
  }

  checkAll() {
    this.connections.forEach((connection) => {
      if (!connection.isAlive) {
        return connection.terminate();
      }

      connection.isAlive = false;
      connection.ping("");
    });
  }

  remove(id) {
    this.connections.delete(id);
  }

  close() {
    clearInterval(this.interval);
  }
}

module.exports = NotifierService;

routes.js

const express = require("express");

const router = express.Router();
module.exports = (webSocketNotifier) => {
  router.post("/newPurchase/:id", (req, res, next) => {
    webSocketNotifier.send(req.params.id, "purchase made");
    res.status(200).send();
  });
  return router;
};

www.js

const server = require("../server/app")();

const port = process.env.PORT || "4000";

server
  .listen(port)
  .on("listening", () =>
    console.log("info", `HTTP server listening on port ${port}`)
  );

module.exports = server;