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H. Díaz
Asked: 2020-03-21 04:10:48 +0800 CST 2020-03-21 04:10:48 +0800 CST

Doubt NodeJS, import modules

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I was taking a look at NodeJS , when I came across this example:

module.exports = function(app){
    var controllers = require('../controllers/controllers.js');
    app.get('/libros', controllers.findAll);
}

The point is that this bit of code goes in the routes.js file . After testing it, I see that it works, but I don't quite understand why it can be used appas a parameter when it hasn't even been imported.

nodejs

1 Answers

  1. Best Answer

    The code you've posted looks a lot like in applications built with Express. You are simply passing an instance of Express already configured to a module where the routes that Express will handle are mapped.

    I don't quite understand why app can be used as a parameter when it hasn't even been imported

    Well, you don't need to directly import something to be able to use it . If you export a function from module B , then when you import said module you import the function and, like any function, you can pass parameters to it . There is no magic or anything in this, nor is it a special feature of CommonJS (library for modularization of JavaScript code adapted and implemented in Node.js), JavaScript just works like this. In Java for example, it is the same; in class A you import a class, create an object and you can pass this as a parameter in the method of another class.

    On the other hand, that approach is not very flexible. It's best to map all routes using the router provided by Express:

    const router = require('express').Router();
const Controller = require('../controllers/index');

router
  .get('/', Controller.index)
  .get('/:id', Controller.findById)
  .post('/', Controller.create)
  .patch('/:id', Controller.update)
  .delete('/:id', Controller.remove);

    This effectively separates your app into layers. Preferably, don't add handlers directly to routes because it's not the direct responsibility of the router; the responsibility lies with the handlers and it is good practice to have them in a separate layer so that you minimize dependencies between them.

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