https://stackoverflow.com/questions/38172337/using-require-without-export
In dpe-api/src/server.js, we directly require the index.js file of @bbc/digital-paper-edit-api.
The index.js does not specify any exports, so how does it work?
In JS, when one imports a module without an export, the module is still run. This is how @bbc/digital-paper-edit-api can simply run without explicitly being assigned and executed. Since the aforementioned dependency also relies on variables such as process.env.PORT to specify the behaviour of the Express server, we can pass the variables in, like PORT=4000 npm start to start the server at the specified port.
The caveat with this way of importing / exporting is that it is not possible to access the variables inside the imported dependencies. If you want to actually interact with the variables inside the module, export them. Another more dangerous aspect of this is that when a variable is not assigned with var in the imported dependency, it is treated as a global variable. So there are dangers of hidden overwriting of variables. It's not recommended.