Importing Node.js Core Modules

Node.js comes with dozens of built-in modules. These built-in modules sometimes referred to as core modules, give you access to tools for working with the file system, making HTTP requests, creating web servers, and more! In this lesson, you’ll learn how to load in those core modules and use them in your code.
Importing Node.js Core Modules

To get started, let’s work with some built-in Node.js modules. These are modules that come with Node, so there’s no need to install them.
The module system is built around the function. This function is used to load in a module and get access to its contents. is a global variable provided to all your Node.js scripts, so you can use it anywhere you like!
Let’s look at an example.

const fs = require('fs')

fs.writeFileSync('notes.txt', 'I live in Viet Nam')

The script above uses require to load in the fs module. This is a built-in Node.js module that provides functions you can use to manipulate the file system. The script uses writeFileSync to write a message to notes.txt. After you run the script, you’ll notice a new notes.txt file in your directory. Open it up and you’ll see, “I live in Viet Nam!”.

You can reference

Node.js documentation 

Node.js fs documentation