Use multiple JS files as defaults for nconf: https://github.com/indexzero/nconf/issues/96

all.js

module.exports = {
  ENV: 'set by development.js',
  ARG: 'set by development.js',
  DEV: 'set by development.js'
};

config.js

var config = require('nconf');
var extend = require('node.extend');
var env = process.env.NODE_ENV || 'development';

config.use('memory')
  .env('__')
  .argv()
  .defaults(extend(true, {}, require('./environments/all'), require('./environments/' + env)));

/**
 * Run this on the command line:
 * $ ENV='set by environment variable' node config.js --ENV 'set by command line arg' --ARG 'set by command line arg'
 * 
 * Output:
 * ENV: set by environment variable
 * ARG: set by command line arg
 * DEV: set by development.js
 * ALL: set by all.js
 */
console.log('ENV: ' + config.get('ENV'));
console.log('ARG: ' + config.get('ARG'));
console.log('DEV: ' + config.get('DEV'));
console.log('ALL: ' + config.get('ALL'));

development.js

module.exports = {
  ENV: 'set by all.js',
  ARG: 'set by all.js',
  DEV: 'set by all.js',
  ALL: 'set by all.js'
};