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In CodeIgniter 4, libraries are reusable classes that help developers organize application logic into clean, modular components.

While CodeIgniter 4 comes packed with helpful built-in libraries, you’ll often need to create your own libraries to handle specific, reusable functionality unique to your application. Custom libraries are simply PHP classes placed inside your app/Libraries/ folder.

In this guide, we’ll learn how to create, load, and use custom libraries in CodeIgniter 4.

Let’s get started.

⚪ Why Create a Custom Library?

To encapsulate repeated logic (like calculations, formatting, API calls) into a dedicated class.
To keep controllers and models clean, focused, and manageable by removing extra utility code.
To reuse the same functionality across multiple controllers and services without code duplication.
To improve your application’s scalability and maintainability as your project grows.
To promote modular, well-organized code structure in your CodeIgniter 4 applications.

⚪ How to Create a Custom Library?

Creating a custom library in CodeIgniter 4 is straightforward. You need to create a new PHP class file inside the app/Libraries/ directory. This class should use the appropriate namespace and contain any methods you wish to reuse across your application.

Example: app/Libraries/MyCustomLibrary.php

<?php
namespace App\Libraries;

class MyCustomLibrary
{
    public function greet($name)
    {
        return 'Hello, ' . esc($name) . '!';
    }
}

⚪ Loading a Custom Library

There are two main ways to load a custom library in CodeIgniter 4:

📍 Direct Instantiation

You can directly create an instance of your library wherever needed:

$myLibrary = new \App\Libraries\MyCustomLibrary();
echo $myLibrary->greet('Sanjay');

📍 Register as a Service (Recommended)

For global use, you can register your library as a service inside app/Config/Services.php:

public static function myCustomLibrary()
{
    return new \App\Libraries\MyCustomLibrary();
}

Then, access it like this:

$myLibrary = \Config\Services::myCustomLibrary();
echo $myLibrary->greet('Sanjay');

⚪ Example: A Simple Math Library

Let’s create a practical custom library for basic math operations.

File: app/Libraries/MathLibrary.php

<?php
namespace App\Libraries;

class MathLibrary
{
    public function add($a, $b)
    {
        return $a + $b;
    }
}

Usage:

$math = new \App\Libraries\MathLibrary();
echo $math->add(10, 5); // Outputs: 15

You can also register this MathLibrary as a service if you need to access it frequently.

⚪ Conclusion

Creating custom libraries in CodeIgniter 4 is a simple yet powerful way to manage reusable, application-specific functionality. It keeps your code organized, promotes modularity, and reduces duplication.

Whether it’s for utilities, data processing, or API integrations — custom libraries make your CodeIgniter 4 applications cleaner and easier to scale.