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

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);