codex-lv3-may-2025

📦 Mini Lesson: Importing Functions with Node.js

🎯 Goal

Learn how to separate your code into different files and import functions from one file into another using Node.js modules. This helps you organize your code and reuse functions across multiple files.

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📚 Two Module Systems

JavaScript has two main ways to import and export code:

1. CommonJS (older style):

// Export
module.exports = add;

// Import
const add = require('./add');

2. ES6 Modules (modern style):

// Export
export default add;

// Import
import add from './add.js';

In this lesson, we’ll use ES6 modules (the modern style). This requires adding "type": "module" to your package.json file, or using .mjs file extensions.

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🧩 Step 1: Why Separate Code into Files?

When your code gets bigger, it’s better to organize it into separate files:

• Reusability — Write a function once, use it in many places
• Organization — Keep related code together
• Maintainability — Easier to find and fix bugs
• Teamwork — Multiple people can work on different files

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🧠 Step 2: Exporting a Function

Before you can import a function, you need to export it from the file where it’s defined.

Example: add.js

// Your function code here...

// Export the function so other files can use it
export default add;

The export default line makes the function available to other files.

Note: The add function is just a simple example to demonstrate the import/export pattern. In real projects, you’d use more useful functions like:

• toSnakeCase() — Converting strings to snake_case (from the previous lesson)
• formatDate() — Formatting dates
• validateEmail() — Validating email addresses
• calculateTotal() — Business logic calculations
• And many other reusable utility functions

The import/export pattern works the same way regardless of what your function does!

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💬 Step 3: Importing from the Same Directory

When your files are in the same directory (next door to each other), you use a relative path starting with ./.

Example: Same Directory Structure

my-project/
  ├── add.js
  └── app.js

add.js (the function file):

// Your function code here...

export default add;

app.js (the file that uses the function):

// Import the function from the same directory
import add from './add.js';

// Now you can use it!
let result = add(2, 3);
console.log(result); // 5

Key points:

• ./ means “current directory”
• import add from './add.js' looks for add.js in the same folder
• You need to include the .js extension in ES6 modules

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🎁 Step 4: Importing from a Subdirectory

When your function is in a subdirectory (a folder inside your project), you need to specify the path with ./ followed by the folder name.

Example: Subdirectory Structure

my-project/
  ├── app.js
  └── helpers/
      └── math.js

helpers/math.js (the function file):

// Your function code here...

export default add;

app.js (the file that uses the function):

// Import from the helpers subdirectory
import add from './helpers/math.js';

// Now you can use it!
let result = add(5, 7);
console.log(result); // 12

Key points:

• ./helpers/math.js means “look in the helpers folder for math.js”
• The path always starts with ./ when it’s a relative path
• You can nest folders deeper: ./utils/helpers/math.js

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🧰 Step 5: Understanding Module Paths

There are different ways to specify where to find a module:

Path Type	Example	Meaning
Relative	./add	Same directory
Relative	./helpers/math	Subdirectory
Relative	../utils/helper	Parent directory (go up one level)
Absolute	/Users/name/project/helper	Full path from root
Node Module	fs or path	Built-in Node.js module

For now, focus on relative paths starting with ./ for files in your project.

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🧩 Step 6: Complete Example

Let’s see a complete example with multiple files:

File Structure:

my-project/
  ├── app.js
  └── helpers/
      └── math.js

helpers/math.js:

// Your function code here...

// Export both functions
export { add, subtract };

app.js:

// Import both functions from the helpers folder
import { add, subtract } from './helpers/math.js';

// Use them
console.log(add(5, 3)); // 8
console.log(subtract(10, 4));  // 6

Note: When exporting multiple functions, you use export { add, subtract } and can import specific ones using destructuring { add, subtract }.

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⚡ Challenges

1. Import Your Snake Case Function:
   • Create a helpers/ folder
   • Create helpers/string-convert.js with your toSnakeCase function from the previous lesson
   • Export the toSnakeCase function
   • Import and use it in app.js to convert “Hello World” to snake case
2. Multiple Functions:
   • Add toKebabCase and toCamelCase to your helpers/string-convert.js file
   • Export all three functions
   • Import and use them in app.js
3. Nested Folders:
   • Create utils/helpers/ structure
   • Move your string-convert.js file there
   • Import toSnakeCase using ./utils/helpers/string-convert

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📝 Summary

Concept	Description	Example
Export	Making a function available to other files	export default add;
Import (Same Dir)	Getting a function from the same folder	import add from './add.js';
Import (Subdirectory)	Getting a function from a subfolder	import add from './helpers/math.js';
Multiple Exports	Exporting multiple functions	export { add, subtract };
Relative Path	Path starting with ./ that’s relative to current file	./helpers/math.js
Module	A file that exports functions/variables for reuse	math.js

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🙏 Acknowledgement

This lesson was created with assistance from GPT-5.