How do I share functionality between my expressjs routes? - node.js

Question

Suppose I have two routes in my expresjss project: users.js and profiles.js.
users.js:
var express = require('express');
var router = express.Router();
/* GET users listing. */
router.get('/', function(req, res, next) {
var extra = something_nice();
res.json( { three: 'four', extra: extra } );
});
module.exports = router;
profiles.js:
var express = require('express');
var router = express.Router();
/* GET profiles listing. */
router.get('/', function(req, res, next) {
var extra = something_nice();
res.json( { one: 'two', extra: extra } );
});
module.exports = router;
Notice how I have something_nice() method there, which ideally I would define in a 'super class' if this were regular OOP like rails controllers.
How do I go about this with node + expressjs? My assumption was I should create a new module, and require it here, but is this the best practice?

Answer 1

You solve it in the same way. Using a class:
class SomethingCool {
somethingNice() {
return 'cool!';
}
}
module.exports = SomethingCool;
In your route:
var express = require('express');
var router = express.Router();
var SomethingCool = require('./something-cool.class');
const something = new SomethingCool();
/* GET profiles listing. */
router.get('/', function(req, res, next) {
var extra = something.somethingNice();
res.json( { one: 'two', extra: extra } );
});
module.exports = router;
Same principles should apply regardless of language (as long as they have support for classes, or class-like objects).
Also you don't even need a class here:
function somethingNice() {
// some logic
}
// inside file1
router.get('/', (req, res, next) => {
const extra = somethingNice();
res.json({ one: 'two', extra });
});
You can reuse functions where you like/need, just ensure they're exported using module.exports (if using in a different file/module).
Have a read over this when you have time:
https://dev.to/santypk4/bulletproof-node-js-project-architecture-4epf
It may be able to answer some of the questions you later have about design, structure and reusing logic in different areas.
EDIT: an explanation on how middleware can help in certain situations.
https://expressjs.com/en/guide/using-middleware.html
function isUserAdmin(user) {
// some logic for determining
}
app.use((req, res, next) => {
if (isUserAdmin(req.user)) {
req.role = 'Admin';
}
next();
});
This is a simplified example, in reality you'd also need to add the req.user.
The thing to understand here, is your ability to use middleware to reuse functionality.
However, if you wanted something a little more specific to the route, then I'd opt to use a class (following the Service pattern from other reference link).
Another (more common) example, consider a logger, it outputs which endpoint was requested and with what method:
// file: service/logger.service.js
class LoggerService {
log(message) {
console.log(message);
}
}
module.exports = MyLogger;
// file: middleware/logger.middleware.js
const logger = new MyLogger();
app.use((req, res, next) => {
const path = req.path;
const method = req.method;
logger.log(`${path} ${method}`);
return next();
});
This way, your route never needs to know about the logger, or what function it has, you can plug an unlimited amount of additional functionality this way.
Although it's more suited for generic tasks, like checking a user has authenticated (for example), or is authorized, but it's certainly not limited to only that type of use.
If you really want a super class, then use a singleton:
class SuperClass {
constructor() {
this.someOtherClass = new UserClass();
this.someSecondClass = new ProjectClass();
}
doSuperWork() {
}
}
module.exports = new SuperClass();
I'll say though, it may not be the best solution (super classes in general).

Answer 2

You can create a function that accepts the router instance as an argument and can implement your common logic inside that function. Javascript uses composition instead of inheritance.
module.exports=function (router){
router.get('/', function(req, res, next) {
var extra = something_nice();
res.json( { one: 'two', extra: extra } );
});
}