Modular programming in node js

You can use the express middlewares and the default module system in node.js to achieve this.It is a good practice to keep the code modular and separated. One common way to do this is add separate folders for all different routes/controllers(employee in your case) something like this

app.js

const express = require('express')
const app = express()

const employeeController = require('./controller/Employee');
const managerController = require('./controller/Manager');

app.use('/employee', employeeController);
app.use('/manager', managerController);


app.listen(3000, () => console.log('App listening on port 3000!'))

./controller/Employee/index.js

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

router.get('/list', (req, res) => {
  res.send('Employee list')
});
router.get('/view', (req, res) => {
  res.send('Employee view')
});

module.exports = router

./controller/Manager/index.js

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

router.get('/list', (req, res) => {
  res.send('Manager list')
});
router.get('/view', (req, res) => {
  res.send('Manager view')
});

module.exports = router

you can even get a readymade boilerplate MVC code structure by using express-generator here https://expressjs.com/en/starter/generator.html .However i reccommed to structure your project based on your needs.

One of greatest things in node.js is its module system (you can read about it in docs: https://nodejs.org/api/modules.html), which gives you like every option of granularity you would like to take, from one-thousand-lines files to files that export just one constant.

So just split code in files, module.exports = thatthingyouwanttoexport and then require('./it') back in app.js. If you do it at top-level, not inside any callback in app.js, then it would be done right at the start of your application.

Few catches:

• required modules are cached, so requiring it twice doesn't execute your files twice, it can be useful (e.g. for singletons), but it's still thing to note;
• you export only things that you're exporting, so no globals

One useful pattern is to export function, which takes arguments and does initialization when called, like this:

//accum.js
var start = 0
module.exports = function initaccum(step) {
    return function accum() {
        start += step;
        return start;
    }
}

//app.js
var accum = require('./accum.js')(1);
var http = require('http')
http.createServer(function(req, res) {
    res.end(accum());
}).listen(8080);

Hope this helps.