Node

                        $ npm install config
                        $ mkdir config
                        $ vi config/default.json
                        
                        $ npm i --save-dev @types/config
                    

                            {
                                "database":{
                                    "uri":"DATABASE_URI"
                                },
                                "authentication": {
                                    "cryptKey": "AUTHENTICATION_CRYPT_KEY"
                                }
                            }
                        

                            const config = require('config');

                            const dbConfig = config.get('Customer.dbConfig');
                            db.connect(dbConfig, ...);

                            if (config.has('optionalFeature.detail')) {
                                const detail = config.get('optionalFeature.detail');
                            }
                        

                            import config from 'config';

                            const connectionString = config.get<string>('database.uri');