The system on which we develop our app is the development environment or platform—the system could be your personal laptop or desktop. Apart from development, we may use such a system for browsing, sending e-mails, image editing, playing games, listening to music, watching movies, and so on. We would not host our app on such a system, would we?
When we are ready to share our app with the world, the recommended and common practice is to use a dedicated system for hosting it, which may or may not be shared by other apps.
So how does Express know it is in the production environment?
For more information about
NODE_ENV and the various modes of Express, refer to the Express in different environments section in Chapter 2, Your First Express App.