Script to load up environment variables into the application

env.js

const fs = require('fs');
const yaml = require('js-yaml');
const uuid = require('node-uuid');

const appYamlConfigFile = 'app.yaml';
const requiredEnvVariables = ['DATABASE_URL'];

// default configuration
process.env.API_VERSION = 1;
['SESSION_SECRET_KEY', 'WEB_TOKEN_SECRET'].forEach((configVar) => {
  process.env[configVar] = uuid.v4();
});

// if an env has not been provided, default to development
if (!('NODE_ENV' in process.env)) process.env.NODE_ENV = 'development';

if (process.env.NODE_ENV === 'development') {
  const envKeys = Object.keys(process.env);
  const allRequiredEnvVariablesExist = requiredEnvVariables.every(
    (variable) => envKeys.indexOf(variable) !== -1
  );

  // if the requiredEnvVariables have not been added
  // maybe by GAE or Heroku ENV settings
  if (!allRequiredEnvVariablesExist) {
    if (fs.existsSync(appYamlConfigFile)) {
      // Get the rest of the config from app.yaml config file
      const appEnvConfigurations = yaml.safeLoad(fs.readFileSync(appYamlConfigFile, 'utf8'));
      Object.keys(appEnvConfigurations).forEach((key) => {
        process.env[key] =
          typeof appEnvConfigurations[key] !== 'string'
            ? JSON.stringify(appEnvConfigurations[key])
            : appEnvConfigurations[key];
      });
    } else {
      throw new Error(`
      Missing app.yaml config file used while in development mode
      It should have contents similar to the example below:
      app.yaml
      -------------------------
      SECRET_CODE: '000000'
      SECRET_KEY: 'a8eac82d7ac1461ba0348b0cb24d3f8140d3afb9be864e56a10d7e8026eaed66'
      ENDPOINT: 'http://merchant-endpoint.com/mpesa/payment/complete'
      DATABASE_URL: 'mongo+srv://eugene:password@localhost:27017'
      -------------------------
    `);
    }
  }
}

Now you can add all your env variables in an app.yaml in the same root folder as this:

SECRET_CODE: '000000'
SECRET_KEY: 'a8eac82d7ac1461ba0348b0cb24d3f8140d3afb9be864e56a10d7e8026eaed66'
ENDPOINT: 'http://merchant-endpoint.com/mpesa/payment/complete'
DATABASE_URL: 'mongo+srv://eugene:password@localhost:27017'

Load it up in the index file of your nodejs, expressjs likely, application with require('./env')