Core modules are modules that are built into Node.js and come automatically with its installation. These modules include bare minimum functionalities of Node.js and are compiled into its binary distribution. You can load these modules into your program by using the require function

Some examples of core modules in Node.js include http, fs, path, os, and buffer among others. These modules provide basic functionalities like creating an HTTP server (http), handling the file system (fs), dealing with file paths (path), providing information about the operating system (os), and handling binary data (buffer) .

Global modules are Node.js packages that are installed on your system rather than your project directory. This means that they can be used anywhere on your local computer.There is no need to import them into your project.

For example, if you install the nodemon package globally, you can use it anywhere on your computer. You don’t need to import it into your project. You can simply run nodemon in your terminal to start the server.

console.log("Hello World")

console.log is a global module

In Node.js, a non-global module refers to a module that is not part of the Node.js core and is not installed globally. Instead, it is created locally within your Node.js application. These modules can be a single file or a collection of multiple files/folders. And you need to import them into your project before you can use them.

• Example 1 :

const fs = require('fs')
fs.writeFileSync('hello.txt', 'Hello World')

fs (file system) is a non-global module and we use this module to create a file named hello.txt and write "Hello World" in it.

• Example 2 :

console.log("Our directory is " + __dirname)
//output : Our directory is C:\Users\Subham Maity\Desktop\Node.js\Node.js Tutorial

__dirname is a non-global module and we use this module to get the current directory path.

console.log("Our file name is " + __filename)
//output : Our file name is C:\Users\Subham Maity\Desktop\Node.js\Node.js Tutorial\index.js

__filename is a non-global module and we use this module to get the current file path.

If you want to import only a specific function from a module, you can use the destructuring syntax. For example, if you want to import the writeFileSync function from the fs module, you can do it like this:

const { writeFileSync } = require('fs')
writeFileSync('hello.txt', 'Hello World')

or

const fs = require('fs').writeFileSync;
fs('hello.txt', 'Hello World')

• here if you want you can change the variable name of the function like this :

const abc = require('fs').writeFileSync;
abc('hello.txt', 'Hello World')