Toy websocket client

app.js

const express = require('express');
const app = express();
const WebSocket = require("ws");


app.get('/', function (req, res) {
    res.send('This is not really a web page.');
});

const port = 3997
const wsPort = 3998
app.listen(3997, function () {
    console.log(`Example app listening on port ${port}!`);

    let receivedEvents = 0;
    const ids = [
        "0x60674ffbef620598f735d6c9c120b422c48830a6",  
        "0x60674ffbef620598f735d6c9c120b422c48830a6", 
        "0x4c9178b95977de41690c6067a771388147b3a70b" 

    ]
    try {
        const ws = new WebSocket(`ws://localhost:${wsPort}`)
            .on("message", (msg) => {
                const decoded = JSON.parse(msg);
                switch (decoded.type) {
                    case "connected":
                        console.log("connected")
                        ws.send(JSON.stringify({ ids: ids }));
                        break;
                    case "subscribed":
                        console.log("Subscribed")
                        break;
                    case "data":
                    case "changed":
                        receivedEvents++;
                        console.log("new event: ", decoded);
                        break;
                    default:
                        ws.close();
                }
            })
            .on("ping", () => {
                console.log("got ping");
            })
            .on("close", () => {
                console.log("woohoo!");
            });
    } catch (e) {
        console.log("error: ", e)
    }

});

package.json

{
  "name": "untitled",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "node app.js",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dev-dependencies": {
    "body-parser": "^1.19.0",
    "express": "^4.17.1",
    "ws": "^7.3.1"
  },
  "dependencies": {
    "body-parser": "^1.19.0",
    "express": "^4.17.1",
    "ws": "^7.3.1"
  }
}