As you know, there is a famous idiom on Python, which is
if __main__ == "__main__":.
The inside of if is only executed when it is directly launched by python command. It’s the way that we make command line interface which is compatible to module.
On Node.js, we can do same thing.
You can see next if you run them.
$ node app.js started: app.js $ node cli.js started: cli.js
module.parent is the way. If it’s directly launched, it becomes
null. Very simple.