socket.io with express (not found error)

If you encounter error like below.

GET /socket.io/socket.io.js 404

Then you have to make sure whether socket.io invoked the listen method or express did. Of course, socket.io must invoke the listen method.

main.js
-------

const express = require('express')
...

const app = express()

...setting for express...

module.exports = require('./socket.io.methods')(app)

server.js
---------

const config = require('../config')
const server = require('../server/main')
const debug = require('debug')('app:bin:server')
const port = config.server_port

server.listen(port)
debug(`Server is now running at http://localhost:${port}.`)