Using socket.io in Express 4 and express-generator's /bin/www

Here is how you can add Socket.io to a newly generated Express-Generator application:

1. Create a file that will contain your socket.io logic, for example socketapi.js:

socketapi.js:

const io = require( "socket.io" )();const socketapi = {    io: io};// Add your socket.io logic here!io.on( "connection", function( socket ) {    console.log( "A user connected" );});// end of socket.io logicmodule.exports = socketapi;

2. Modify your bin/www launcher. There are two steps: requiring your Socket.io api and attaching the HTTP server to your socket.io instance right after creating the HTTP server:

bin/www:

/** * Module dependencies. */var app = require('../app');var debug = require('debug')('socketexpress:server');var http = require('http');let socketapi = require("../socketapi"); // <== Add this line/** * Get port from environment and store in Express. */var port = normalizePort(process.env.PORT || '3000');app.set('port', port);/** * Create HTTP server. */var server = http.createServer(app);socketapi.io.attach(server); // <== Also add this line(...)

3. Then you just need to add the Socket.io client in your index.html. Add the following just before the </body> closing tag:

index.html

    (...)    <script src="/socket.io/socket.io.js"></script>    <script>        var socket = io();    </script></body></html>

4. Finally you can start your Express server:

• Unix based: DEBUG=myapp:* npm start
• Windows: set DEBUG=myapp:* & npm start

Note 1

If for any reason you need access to your socket api in your app.js, then you could instead import your socket api in app.js, and re-export it:

app.js

var express = require('express');var socketapi = require("./socketapi"); // <== Add this line(...)// You can now access socket.io through the socketapi.io object(...)module.exports = { app, socketapi }; // <== Export your app and re-export your socket API here

Then in your bin/www launcher, instead of importing your socket api on its own line, just import it along your app:

bin/www

var {app, socketapi} = require('../app'); // <== Import your app and socket api like this(...)var server = http.createServer(app);socketapi.io.attach(server); // <== You still have to attach your HTTP server to your socket.io instance

Note 2This answer was updated to work with the latest Express Generator (4.16 at time of writing) and latest Socket.io (3.0.5 at time of writing).

A little different approach to initiate socket.io, it groups all related code in one place:

bin/www

/** * Socket.io */var socketApi = require('../socketApi');var io = socketApi.io;io.attach(server);

socketApi.js

var socket_io = require('socket.io');var io = socket_io();var socketApi = {};socketApi.io = io;io.on('connection', function(socket){    console.log('A user connected');});socketApi.sendNotification = function() {    io.sockets.emit('hello', {msg: 'Hello World!'});}module.exports = socketApi;

app.js

// Nothing here

In this way all socket.io related code in one module and function from it I can invoke from anywhere in application.

It turns out it really was some basic sintax problem.... I got these lines from this socket.io chat tutorial...

on ./bin/www, just after var server = app.listen(.....)

var io = require('socket.io').listen(server);require('../sockets/base')(io);

so now I create the ../sockets/base.js file and put this little fellow inside it:

module.exports = function (io) { // io stuff here... io.on('conection..... }

Yeah! Now it works... So i guess i really had no option other than starting socket.io inside /bin/www , because that is where my http server was started. The goal is that now i can build socket functionality in other file(s), keeping the thing modular, by require('fileHere')(io);

<3