ws-simple

// server.js
const Server = require('ws-simple')

const server = new Server({ port: 3000 })

server.on('connection', socket => {
  // Receive message from client
  socket.on('message', message => {
    message // output: 'foo'
    // Send message to client
    socket.send('bar')
  })
})

// client.js
const socket = new WebSocket('ws://127.0.0.1:3000')

socket.addEventListener('open', () => {
  console.log('connected')
})

// Receive message from server
socket.addEventListener('message', e => {
  console.log(e.data)
})

// Send message to server
sendMsgBtn.addEventListener('click', () => {
  socket.send('foo')
})