express configuration

https://hackernoon.com/the-practical-guide-for-building-rest-api-in-nodejs-and-mongodb-include-passport-and-jwt-476720b70da0

const devConfig = {};
const testConfig = {};
const prodConfig = {};
const defaultConfig = {
  PORT: process.env.PORT || 3000,
};
function envConfig(env) {
     switch (env) {
         case 'development':
             return devConfig;
         case 'test':
             return testConfig;
         default:
             return prodConfig;
     }
 }
 
 //Take defaultConfig and make it a single object 
 //So, we have concatenated two objects into one 
 export default { ...defaultConfig,
     ...envConfig(process.env.NODE_ENV),
 };