Node.js Modules

Why Use Modules?

• Encapsulation: Keeps code separate and focused on specific tasks.
• Reusability: Allows functions and logic to be reused across files.
• Maintainability: Easier to manage and debug smaller modules.
• Scalability: Supports structured design for larger applications.

Types of Modules in Node.js

1. Built-in Modules: Included by default (e.g., fs, http, path).
2. User-defined Modules: Custom files created by developers.
3. Third-party Modules: External libraries installed via npm (e.g., express, moment).

1. Built-in Modules

Node.js includes a set of core modules you can import directly.

Explanation:

• require("fs") imports Node’s file system module.

2. User-defined Modules

Create and export functions from custom files.

Step 1: Create Module (math.js)

Step 2: Use the Module (app.js)

Explanation:

• module.exports exposes the functions.
• require("./math") imports the module.

3. Third-party Modules

Install using npm and require in your code.

Step 1: Install

Step 2: Use

Explanation:

• Useful for working with dates, strings, utilities, etc.
• Modules are placed inside node_modules/ folder.

Module Caching in Node.js

Once a module is loaded, it is cached. This avoids reloading it on every require() call, improving performance.

Directory Structure Example

exports vs module.exports

• exports is a shortcut to module.exports.
• Don’t assign a new object to exports; modify module.exports directly.

Correct:

Incorrect:

Best Practices

• Keep each module focused on one responsibility.
• Use consistent file naming.
• Avoid circular dependencies.
• Separate logic into config, utils, routes, etc.

Key Takeaways

• Node.js modules improve organization and maintainability.
• Use require() to import and module.exports to expose code.
• Built-in, custom, and third-party modules support modular development.
• Third-party libraries enhance functionality and reduce development time.
• Caching and proper design patterns make modules efficient and scalable.