config.js

var _ = require('underscore');

var config = require('../config');

var envPrefix = 'PREFIX_'
var envPrefixLen = envPrefix.length;

var envKeys = _.chain(config.base).keys().map(function(key){return envPrefix + key;}).value();

var procEnvOverrides = {};
_.chain(process.env).pick(envKeys).each(function(val, key) {
  var configKey = key.substr(envPrefixLen);
  procEnvOverrides[configKey] = val;
});

var nodeEnvOverrides = config[process.env.NODE_ENV];

module.exports = _.extend(config.base, nodeEnvOverrides, procEnvOverrides);

config.json

{
  "base": {
    "DB_HOST": "localhost",
    "DB_NAME": "mydb"
  },
  "development": {
  },
  "production": {
  }
}