Modules in Node.js | Lecture 4

 

Here are notes on Modules in Node.js:

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Modules in Node.js

What are Modules?

• Modules are reusable blocks of code that help organize functionality into separate files and libraries.
• Node.js uses CommonJS modules by default.

Types of Modules in Node.js:

1. Built-in Modules:
• Pre-installed modules in Node.js.
• Examples: http, fs, path, os, events.
2. User-defined Modules:
• Custom modules created by developers to structure application code.
3. Third-party Modules:
• External libraries installed via npm.
• Example: express, lodash.

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Using Modules in Node.js:

1. Importing a Module:
• Use the require() function to load a module.
• Syntax:

o   const moduleName = require('module-name');

2. Exporting from a Module:
• Use module.exports or exports to expose functionality.
• Syntax:

o   // In a module file (example: math.js)

o   module.exports = {

o       add: (a, b) => a + b,

o       subtract: (a, b) => a - b,

o   };

3. Using the Exported Module:
• Import and use the exported functions or objects.

o   // In another file (example: app.js)

o   const math = require('./math'); // './' indicates a relative path

o   console.log(math.add(2, 3)); // Outputs: 5

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Built-in Modules Examples:

1. fs (File System Module):
• Handles file operations.

o   const fs = require('fs');

o   fs.writeFileSync('example.txt', 'Hello, Node.js!');

o   console.log(fs.readFileSync('example.txt', 'utf-8'));

2. http (HTTP Module):
• Creates web servers.

o   const http = require('http');

o   const server = http.createServer((req, res) => {

o       res.write('Hello from the HTTP module!');

o       res.end();

o   });

o   server.listen(3000, () => console.log('Server running on port 3000'));

3. path (Path Module):
• Provides utilities for file and directory paths.

o   const path = require('path');

o   console.log(path.basename('/folder/example.txt')); // Outputs: example.txt

4. os (Operating System Module):
• Provides system-related information.

o   const os = require('os');

o   console.log(os.platform()); // Outputs: platform (e.g., 'linux', 'win32')

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Creating and Using a Custom Module:

1. Create a Module:
• File: greet.js

o   function sayHello(name) {

o       return `Hello, ${name}!`;

o   }

o   module.exports = sayHello;

2. Use the Module:
• File: app.js

o   const greet = require('./greet');

o   console.log(greet('John')); // Outputs: Hello, John!

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Third-party Modules Example:

• Install and use the lodash library:

·        npm install lodash

·        const _ = require('lodash');

·        const arr = [1, 2, 3, 4, 5];

·        console.log(_.shuffle(arr)); // Outputs: shuffled array

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Advantages of Using Modules:

1. Promotes code reusability.
2. Improves maintainability and organization.
3. Encourages modular design.

Let me know if you'd like more examples or in-depth explanations!