server.js

const express = require('express');
const mongoose = require('mongoose');
const socket = require('socket.io');
const message = require('./model/message')

const app = express();

const db = require('./config/keys').mongoURI;

mongoose.connect(db, {useNewUrlParser: true})
  .then(
    io.on("connection", function(socket){
      console.log("Socket Connection Established with ID :"+ socket.id)
      
      socket.on('disconnect', function(){
        console.log('User Disconnected');
      });
    
      let chat = db.collection('chat');
    
          socket.on('SEND_MESSAGE', function(data){
            let message = data.message;
            let date = data.date;
    
            // Check for name and message
            if(name !== '' || date !== ''){
                // Insert message
                chat.insert({message: message, date:date}, function(){
                    socket.emit('output', [data]);
                });
            }
        });
    
        chat.find().limit(100).sort({_id:1}).toArray(function(err, res){
          if(err){
              throw err;
          }
          // Emit the messages
          socket.emit('RECEIVE_MESSAGE', res);
        });
    
    })    
  )
  .catch( err => console.log(err));

const port = 5000;

let server = app.listen(5000, function(){
  console.log('server is running on port 5000')
});

let io =  socket(server);