javascript - Use socket.io in expressjs routes instead of in main server.js file

Question

I have express/nodejs api. I am adding socket.io feature to it. Currently all of my routes are in separate folders and I include them in server.js file and use them as app.use() function.

In server.js file, I also start the express server by listening to a particular port such as 3000 as below.

let server = app.listen(3000);

According to all google searches what I found is that I need to pass server variable to initialize socket.io like following.

let io = require('socket.io')(server);

Now the question is that since it needs this variable then how can I use socket.io in my routes files which are in different folder to emit and receive events from client?

UPDATE

in server.js file

let route = require('./routes/route');

let app = express();

let server = app.listen(3000);

console.log('Listening to port');

let io = require('socket.io')(server);

app.use('/api/1.0/events', route(io));

in route.js file

let express = require('express');

module.exports = (io) => {
    console.log('IO: ', io);
};

UPDATE 2

server.js file

let express = require('express');
let events = require('./routes/events');
let app = express();
let server = app.listen(3000);

let io = require('socket.io')(server);


app.use(function(request, response, next) {
    request.io = io;
    next();
});

app.use('/events', events);

events.js file

let express = require('express');

let Events = require('../models/events');

apiRoutes.post('/new', function(request, response) {
    let newEvent = new Events(request.body);

    newEvent.save((error, result) => {
        if (error) {
            response.json(error);
        } else {
            // console.log('ELSE');
            // request.io.on('connect', socket => {
                // console.log('LISTENING TO SOCKET...');

                request.io.on('EventCreated', data => {
                    console.log('DATA ON Server: ', data);
                });
            // });

            response.json({
                success: true,
                message: 'New event created'
            });
        }
    });
});

Answer 1

There are multiple ways to share the io variable with route files.

1. When you require() in your route file, pass it the io variable as a constructor argument.

2. Use app.set("io", io) so you can then use let io = app.get("io") in any file that has access to the app object.

3. Create a middleware that puts the io object on every req object so you can access it from there any time.

---

Here's an example of passing it as a constructor argument to the router file:

let server = app.listen(3000);
let io = require('socket.io')(server);

// load other routers
app.use(require("./someRouterFile.js")(io));

// in someRouterFile.js
const express = require('express');

module.exports = function(io) {
    let router = express.Router()

    // define routes
    // io is available in this scope
    router.get(...)

    return router;
}

---

Here's an example of the app.set() scheme:

let server = app.listen(3000);
let io = require('socket.io')(server);
app.set("io", io);

Then, anywhere in your routes that you have access to the app object, you can get it with:

let io = app.get("io");

---

Here's an example of using a middleware to set the io object onto every req object so it's available from all routes.

let server = app.listen(3000);
let io = require('socket.io')(server);

// place this middleware before any other route definitions
// makes io available as req.io in all request handlers
app.use(function(req, res, next) {
    req.io = io;
    next();
});

// then in any express route handler, you can use req.io.emit(...)

---

Here's an example of using an argument to the module constructor without middleware:

// in mysocket.js
module.exports = (io) => {
    console.log('IO: ', io);
    io.on('connect', socket => {
       // handle various socket connections here
    });

    // put any other code that wants to use the io variable
    // in here


};

Then, in your main file:

let server = app.listen(3000);
let io = require('socket.io')(server);

// initialize my socketio module and pass it the io instance
require('./mysocket.js')(io);