Nuxt/examples/with-sockets/io/index.js

import http from 'http'
import socketIO from 'socket.io'

const server = http.createServer(this.nuxt.renderer.app)
const io = socketIO(server)

export default function () {
  // overwrite nuxt.listen()
  this.nuxt.listen = (port, host) => new Promise((resolve) => server.listen(port || 3000, host || 'localhost', resolve))
  // close this server on 'close' event
  this.nuxt.hook('close', () => new Promise((resolve) => server.close(resolve)))

  // Add socket.io events
  let messages = []
  io.on('connection', (socket) => {
    socket.on('last-messages', function (fn) {
      fn(messages.slice(-50))
    })
    socket.on('send-message', function (message) {
      messages.push(message)
      socket.broadcast.emit('new-message', message)
    })
  })
}