npm socket io

                                    <script src="https://cdn.socket.io/socket.io-3.0.1.min.js"></script>

                                    var app = require('express')();
var http = require('http').createServer(app);
var io = require('socket.io')(http);

app.get('/', (req, res) => {
  // Ran when a GET request to path '/'
  res.sendFile(__dirname + '/index.html');
});

io.on('connection', (socket) => {
  // Ran when a socket connected
});

http.listen(3000, () => {
  // Ran when server is ready to take requestes
});

                                    // npm i socket.io
const http = require('http')
const express = require('express')
const socketio = require('socket.io')

const app = express()
const server = http.createServer(app)
const io = socketio(server)

const port = process.env.PORT || 3000

server.listen(port, () => {
  console.log(`Server is up on port ${port}!`)
})

                                    // with npm
npm install socket.io

// with yarn
yarn add socket.io

                                    npm install --save socket.io