In the JavaScript modules you have an option to define a configuration value asynchronously.

Async configuration

Using the asyncConfig utility method you can wrap both promises and async functions (a function which returns a promise) whose resolution will be deferred until:

• the final merged configuration structure is built (that's when async functions are executed; see deferConfig)
• the resolveAsyncConfigs utility method has been called and resolved (all asynchronous configurations been resolved)

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),
};

Resolving async configurations

Important! - Never call config.get before resolveAsyncConfigs

It will cause the config object to freeze and will make resolving values impossible.

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');
})();

Note: support of advance syntax will depend on your node version and/or babel configurations