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How to Create Your Own JavaScript Module

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Introduction

JavaScript modules are essential for building scalable, maintainable, and reusable code—especially as your projects grow in complexity. If you're a junior developer or someone just getting started with frontend development, learning how to create your own JavaScript module can elevate the way you structure your applications and websites.

In this tutorial, you'll learn how to build a JavaScript module from scratch using modern ES6+ syntax. We’ll break everything down step-by-step, and use a real-world example: a collapsible side menu system.

Why Use JavaScript Modules?

Before diving into the code, let's look at why modular JavaScript is important:

• Organization: Modules keep related functionality grouped together.
• Reusability: You can reuse your module in multiple projects or files.
• Maintainability: Easier to debug and test.
• Encapsulation: Avoid polluting the global scope.
• Scalability: Crucial for larger applications or team projects.

Now, let’s create a module from start to finish!

Step-by-Step: Creating a JavaScript Module

Step 1: Setup Your Project

Make sure your project supports ES6 modules. In the simplest case (like static HTML), just ensure your "<script>" tag includes the type="module" attribute.

<script type="module" src="js/side-menu.js"></script>

This tells the browser to treat your script as a module, enabling support for "import" and "export" keywords.

Step 2: Write Your Module

Let’s now turn the raw JavaScript for the side menu into a structured module. Save the following code in a file named "side-menu.js":

/**
 * SideMenu Module
 * Handles side navigation dropdown functionality
 */

export const SideMenu = {
  /**
   * Initialize the side menu module
   */
  init() {
    this.setupDropdowns();
  },

  /**
   * Setup dropdown toggle functionality for side menu
   */
  setupDropdowns() {
    const dropdowns = document.querySelectorAll('.navigation-level-1 .sidemenu-dropdown-icon');

    if (dropdowns.length === 0) return;

    dropdowns.forEach(dropdown => {
      dropdown.addEventListener('click', function () {
        const navContainer = dropdown.closest('.navigation-container');
        if (navContainer) {
          navContainer.classList.toggle('submenu-active');
        }
      });
    });
  }
};

Step 3: Use the Module

To actually use your new SideMenu module, import it in your main JavaScript file like this:

import { SideMenu } from './side-menu.js';

document.addEventListener('DOMContentLoaded', () => {
  SideMenu.init();
});

This will initialize the dropdown toggle functionality once the DOM is fully loaded.

Understanding the Module Code

Let’s break down what’s happening in the SideMenu module:

• Export: We use "export const SideMenu" to make it importable from other files.
• init(): A common convention in modular code, "init" is used to initialize the module.
• setupDropdowns(): This method attaches event listeners to dropdown icons to toggle submenus.

This structure keeps your code clean, modular, and scalable. You can easily test, extend, or reuse this module in other parts of your app.

When to Use JavaScript Modules

Use modules whenever you need to:

• Organize related functionality (e.g., menu logic, form validation, API calls)
• Reuse code across pages or projects
• Isolate functionality to avoid global scope conflicts
• Collaborate with other developers on large codebases

As your apps grow, this modular structure becomes more and more important.

Common Mistakes to Avoid

• ❌ Forgetting type="module" in your script tag
• ❌ Trying to use "import" / "export" in non-module scripts
• ❌ Importing from the wrong file path (remember relative paths like './file.js')
• ❌ Not initializing the module with "init()"

Suggested Enhancements

• 🔁 Support for dynamically added DOM elements using MutationObservers
• 🎨 Add animation transitions for submenu appearance
• ✅ Unit test the toggle logic with Jest or Vitest

Conclusion

Creating your own JavaScript module isn’t just a best practice—it’s a powerful way to level up your frontend development skills. By organizing your code into self-contained, reusable modules, you write cleaner and more scalable applications.

This beginner-friendly tutorial showed you exactly how to structure, export, and use a custom ES6 module with a real-world side menu example. Now it's your turn—modularize something in your own project!