null means no-value. When there is no value assigned to an object variable, it means the object doesn’t exist. If you want to delete the contents of an object from memory, you would assign that object to null.
You should always use even-numbered versions marked LTS that says “Recommended for Most Users” on the download page. An even number Node version is 10.x.x LTS, 12.x.x LTS, 14.x.x LTS and so on that you should use when learning or deploying your project to a production environment.
Express JS is a minimal framework for building web applications in Node JS. It makes the process of creating a server simple with built-in methods that’s why Express JS is widely used and is the de facto framework for Node.
It takes around 3 months to fully learn Node JS and be able to build a functional full-stack application. If you already know some other programming, you can get the basics down within a few week’s time