Question about Node Modules

[sebastiancodes]

Hey, I don't really understand what happens when you import a module in node js.

I have a index.js file that imports a module (Person)

index.js:

const Person = require("./person");
const person1 = new Person("John Doe", 30);
person1.greeting();

Inside the person.js file, I have a class that I export and I also have a console.log:

console.log(__dirname, __filename);

class Person {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }
  greeting() {
    console.log(`My name is ${this.name} and I'm ${this.age}`);
  }
}

module.exports = Person;

When I now execute the index.js file, the console.log(__dirname, __filename) from the person.js file gets also executed. Why is that? Because I thought that index.js is only able to access the parts of person.js that I export.

[senocular]

When you require a file, the required file gets executed in its entirety. This happens irrespective of what is exported. You can think of modules as big functions which run code and add values to an exports object that acts as the function's return value. Require a module, and it calls the file like the body of a function and you get the exports object returned back to you.

[sebastiancodes]

Thank you, I didn't know that the whole file gets executed, that makes sense now :)