Nconf is a configuration tool that we will use to create hierarchical/environment configuration files for our application. Let's install Nconf:

npm install nconf --save

The first thing we will do is to move the following hardcoded port number from our Express application into our configuration:

app.set('port', 3000);

Let's create the module ./lib/configuration/index.js, which will allow us to to read configuration data from JSON files. We import the nconf module and define a constructor function, Config. We then load a configuration file based on the current environment and load the default configuration that holds non-environmental configuration data. We also define a function get(key), which accepts a key and returns a value. We will use this function to read configuration data:

var nconf = require('nconf');

function Config(){
  nconf.argv().env("_");
  var environment = nconf.get("NODE:ENV") || "development";
  nconf.file(environment, "config/" + environment + ".json");
  nconf.file("default", "config/default.json");
}

Config.prototype.get = function(key) {
  return nconf.get(key);
};

module.exports = new Config();

Let's write some configuration for our application. Add the following default configuration to ./config/default.json; this will be shared amongst all environments:

{
  "application": {
    "name": "vision"
  }
}

Now add the following configuration to the development, test, and coverage config files: ./config/development.json, ./config/test.json, and ./config/coverage.json.

{
  "express": {
    "port": 3000
  }
}

Let's change our Express server ./lib/express/index.js so that it reads express:port from configuration:

var express = require('express')
  , http = require('http')
  , config = require('../configuration')
  , app = express();

app.set('port', config.get("express:port"));

app.get('/hearbeat', function(req, res){
  res.json(200, 'OK');
});

http.createServer(app).listen(app.get('port'));

module.exports = app;