const asyncConfig = require('config/async').asyncConfig;
const fetchRequest = fetch('/config/services')
  .then(res => res.json());  // Promise example
async function dbSecrets(config, original) {  // async function example
  const doc = await db.collection('config').findOne({service: 'node'});
  return doc.secretKeys;
}
module.exports = {
  mode: 'dev',  // unrelated value
  fromUrl: asyncConfig(fetchRequest),
  fromDatabase: asyncConfig(dbSecrets),
};

const { resolveAsyncConfigs } = require('config/async');
const config = require('config');
resolveAsyncConfigs(config)
  .then(config => require('./main.js'));
// OR - equivalent to:
(async function() {
  await resolveAsyncConfigs(config);
  await import('./main.js');
})();