index.js

module.exports = function(io){
  const express = require('express');
  const router = express.Router();
  
  router.get('/', (req, res, next) => {
    io.emit('welcome', 'Welcome to our website)
  )
}

// So the question is i can emit using io (but io will make it global, i.e all connected sockets will receive this message, but i only want the new ly connected socket to receive the message)
so i must use socket.emit(according to socket.io docs).. buh how can i use socket here when am only passing io.. though if i try using socket in server.js.. after have listened for connection , it will work
but i want to extend it to other routes

server.js

const http = require('http')
const express = require('express')
const app = express();
const server = http.createServer(app).listen(process.env.PORT || 3000, () => {
  console.log(`Server listening on port: ${port}`)
})

const indexRouter = require('./routes/index');

const socketIo = require('socket.io)(server)
socketIo.on('connection', socket => {
    console.log('A user has connected');
    socket.on('disconnect', client => {
        console.log('A client has disconnected');
    });
});

app.use(indexRouter(socketIo));

module.exports = app;

socket-client.js

const socket = io()
socket.on('welcome', {
  document.write(data)
})