Use of !module.parent in nodejs

Question

Can you please explain why we are using !module.parent in node. why Node.js Accessing parent modules

if (!module.parent) {
  app.listen(3000);
  console.log('listening on port 3000');
}

Answer 1

I Found answer. You can use module.parent to determine if the current script is loaded by another script. Example is here :

a.js:

if (!module.parent) {
    console.log("I'm parent");
} else {
    console.log("I'm child");
}

b.js:

require('./a')

run node a.js will output:

I'm parent

run node b.js will output:

I'm child

Answer 2

In hierarchical programming paradigms many tasks are done at higher level of hierarchy of a framework, it provides better performance and efficiency. Same is being applied here. If the parent object of running module is not listening to any port, then this task is done by its child object explicitly.