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In a node application it's common that you start loading some modules like this:

var express = require('express')
  , app     = express()
  , mongodb = require('mongodb')
  , http    = require('http');

Now, let's say you have a routes.js file which looks like this:

module.exports = function(app) {
  app.get('/', function(req, res) {
    res.render('homepage');
  });
  // other routes
};

So when you call that routes.js file, you pass the app var:

require('./routes')(app);

My question is: what is happening there? Is there resource consumption when passing the app variable to the routes module? I know that node.js caches modules, but I would like to know how that affects variables passed between them and I wonder if the following approach is efficient:

Let's start loading some modules, but let's do in a different way:

var _ = {};

_.express = require('express');
_.app     = _.express();
_.mongodb = require('mongodb');
_.http    = require('http');

Routes.js:

module.exports = function(_) {
  _.app.get('/', function(req, res) {
    res.render('homepage');
  });
  // other routes
};

Call to routes.js:

require('./routes')(_);

Obviously the _ variable will be a large one, but it will include anything you may need in any module. So I wonder if the size of the passed variable affects performance, in which case it would be just stupid to pass more data than needed.

I seek for achieving the best achievable performance in my applications while I try to simplify things when writing code, so any advice that may help with this, or any explanation about how this works behind the scenes in node.js will be appreciated.

Thanks in advance.

jorgefpastor
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    I don't want to guarantee anything, but you don't pass the object but its reference. the size of all of the references is the same – David Haim Sep 03 '15 at 11:37
  • If what you say is finally truth (and it makes sense it is), that would be exactly what I wanted to know. I will investigate it. Thanks! – jorgefpastor Sep 03 '15 at 16:53

1 Answers1

2

See here.

tl;dr: objects are passed by reference, not by value. So you are not expanding your memory consumption when you pass the same object multiple times to multiple modules.

Community
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Luis Delgado
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  • It seems it's not purely a pass-by-reference (according to the answer of that question), but it does behave like it would at least for my use case. It's very interesting how it works. Thanks! – jorgefpastor Sep 03 '15 at 17:39