Side: CommonJS/ES6 Modules
There are two ways to import modules:
CommonJS
ES6
CommonJS is the NodeJS default, and follows the syntax:
For imports: const <name> = require(<module name/path to module>);
For exports: module.exports = { <objects/functions to be exported> }

Side: CommonJS/ES6 Modules
ES6 follows the syntax:
For imports:import <name> from <module_name/path>;orimport {<obj/func to import>, <other obj/funcs>} from <module_name/path>; 
For exports:export const obj = ...orexport function myFunc() { ... }or export {<prevDefinedConst>, <prevDefinedFunc>};

Creating a MongoDB Connection
Inside conn.js:
To create an instance, use the constructornew MongoClient(<url>)
url – the socket where we will connect to. The port can be set to anything as long as it is not occupied by another service.

Creating a MongoDB Connection
Inside conn.js:
Two functions are exported:
connectToMongo (callback)
getDb (dbName)
connectToMongo(callback)
Establishes the initial connection to the mongodb process. The connection should be maintained until the main program (e.g., app.js/server.js) is closed
Has to be called before any other operations on the database.
getDb(dbName)
Returns an instance of the database with the specified name. 

Side: Environment Variables
For best practices: config values, credentials, and sensitive information should be stored inside a .env file.
This .env file will then be loaded as environment variables which can then be accessed in NodeJS via:
process.env.<var_name>
In version control (e.g., git), ignore the .env file from your repository.
This is to prevent your credentials from being leaked to the internet!