node3.txt

Chapter 3 – Node.js Modules & File System
1. What Are Modules in Node.js?

Modules are separate files or features that you can include in your Node.js program.
They help break large programs into smaller, reusable parts.

   Node.js has 2 types of modules:

   Built-in Modules →  already available in Node.js

   Custom Modules → created by you

   External Modules → installed using npm

2. Built-in Modules in Node.js

   Some commonly used built-in modules:

   fs → File System

   http → Create server

   path → Work with file paths

   os → Operating system details

   To use a module:

  const fs = require("fs");

3. File System Module (fs)

   This module allows you to:

   Create files

   Read files
 
   Update files

   Delete files

   Rename files

  Examples of FS operations:

fs.writeFile()

fs.appendFile()

fs.readFile()

fs.unlink()

fs.rename()

4. Synchronous vs Asynchronous

Node.js operations are mostly asynchronous (non-blocking).
But every FS operation has a sync version:

Examples:

readFile() → async

readFileSync() → sync

Async is preferred for performance.

5. Creating Your Own Module

Any .js file becomes a module.
You can export functions using:

module.exports = functionName;


And import using:

const fn = require("./myModule");

6. Summary of This Chapter

Modules allow organized coding

Use built-in modules like fs, http, os, path

FS module helps in reading/writing files

Difference between sync & async functions

Custom modules help reuse your own code