Node.js Modules

Node.js Modules

A module in Node.js is a reusable block of code whose existence does not accidentally impact other code.
Modules help you:

✔ Organize your application
✔ Reuse functionality
✔ Keep code clean and manageable
✔ Avoid naming conflicts

Node.js uses a module system called CommonJS.

⭐ Types of Modules in Node.js

1. Built-in Modules (provided by Node.js)
   Example: fs, http, os, path, events

2. User-defined Modules (your own files)

3. Third-party Modules (installed via npm)
   Example: express, moment, mongoose

1️⃣ Creating a Module (User-defined Module)

Every JavaScript file in Node.js is a module.

Example: math.js

✔ module.exports is used to export functions, objects, variables.

2️⃣ Importing a Module

Use require() to import modules.

Example: app.js

⭐ Exporting Multiple Values

math.js

app.js

3️⃣ Built-in Modules

Node.js provides many useful core modules:

💡 a) fs (File System)

💡 b) path

💡 c) http

💡 d) os

💡 e) events

4️⃣ Third-party Modules (npm)

Install:

Use:

⭐ Module Wrapper Function (Important Concept)

Internally, Node.js wraps your module in a function:

This gives each file its own scope — so variables don’t leak globally.

5️⃣ ES Modules (import/export)

Node.js also supports ES6 modules when you use:

• "type": "module" in package.json
  OR

• .mjs file extension

math.mjs

app.mjs

📌 Summary Table

🎯 Why Use Modules?

✔ Code reusability
✔ Better structure
✔ Encapsulation
✔ Easy maintenance