Example of a dev/production/env config system for NodeJS

config-default.js

// These are de default settings
// They may be overriden by the values in cofig-production.js if NODE_ENV=production
// They may also be averriden if an environment variable with the same name is set

// WARNING: Do not include this file directly. Use config.js instead

module.exports = {
	DEBUG: true,
	COMPONENT_NAME: 'PROJECT API',
	HTTP_PORT: 8000,
	MONGODB_URI: 'mongodb://mongo:27017/app'
};

config-production.js

// These settings will apply only if NODE_ENV='production'
// They may be averriden if an environment variable with the same name is set

// WARNING: Do not include this file directly. Use config.js instead

module.exports = {
  DEBUG: false,
  HTTP_PORT: 80
};

config.js

// Example usage assuming HTTP_PORT is set in config-default.js or in config-production.js: 
//
//   if API_HTTP_PORT is set as an environment variable, config.HTTP_PORT will take its value
//   else if HTTP_PORT is set as an environment variable, config.HTTP_PORT will take its value
//   else if NODE_ENV=production and config-production.js contains the key, config.HTTP_PORT will take its value
//   else config.HTTP_PORT will take de value defined in config-default.js
//
// NOTE: Only keys defined in config-*.js will be used
//       Other environment variables will be ignored
// 

const VAR_PREFIX = "API_";

const defaultConfig = require('./config-default.js');
const productionConfig = require('./config-production.js');

var config = {};

// Base config
if(process.env.NODE_ENV == 'production') {
	console.log("Config.js is using production settings");
	config = Object.assign(config, defaultConfig, productionConfig);
}
else {
	config = defaultConfig;
}

// Environment variables will override existing keys
Object.keys(config).forEach(key => {
	if(typeof process.env[VAR_PREFIX + key] != 'undefined') {
		console.log("Using ENV variable", VAR_PREFIX + key);
		config[key] = process.env[VAR_PREFIX + key];
	}
	else if(typeof process.env[key] != 'undefined') {
		console.log("Using ENV variable", key);
		config[key] = process.env[key];
	}
}, {});

module.exports = config;