server.js

const app = require('express')()
const server = require('http').Server(app)
const io = require('socket.io')(server)
const next = require('next')

const port = parseInt(process.env.PORT, 10) || 3000
const dev = process.env.NODE_ENV !== 'production'
const nextApp = next({ dev })
const nextHandler = nextApp.getRequestHandler()

let interval;

const getApiAndEmit = socket => {
  const response = new Date();
  // Emitting a new date. Will be consumed by the client
  socket.emit("FromAPI", response);
};

io.on("connection", (socket) => {
  console.log("New client connected");
  if (interval) {
    clearInterval(interval);
  }
  interval = setInterval(() => getApiAndEmit(socket), 1000);
  
  socket.on("disconnect", () => {
    console.log("Client disconnected");
    clearInterval(interval);
  });
});

nextApp.prepare().then(() => {
  app.get('*', (req, res) => {
    return nextHandler(req, res)
  });

  server.listen(port, err => {
    if (err) throw err
    console.log(`> Ready on http://localhost:${port}`)
  })
})