Guided: Building a Web Component Library

In this Code Lab, you’ll dive into crafting a suite of reusable web components using pure vanilla JavaScript—no frameworks, just the raw power of web standards. Web components are a collection of APIs (Custom Elements, Shadow DOM, and HTML Templates) that enable you to define custom HTML tags with their own encapsulated styles and behavior, like <my-button> or <my-card>. Think of them as modular UI building blocks you can use across projects, whether in a React app, a Vue site, or plain HTML.

You'll start by creating a button and a card component, exploring the essentials through practical, hands-on tasks. By the end of this lab, you’ll understand how web components solve real-world challenges like style conflicts, code duplication, and inconsistent UI design. Web components offer modularity, encapsulation, and reusability, making them ideal for consistent UI elements across applications. They isolate styles and logic, reducing conflicts in large projects.

Meanwhile, in this lab, you’re working in the domain of front-end UI development. Terms like "custom element," "shadow DOM," "slot," and "attribute" will become your toolkit. These concepts let you model UI components after real-world entities—like buttons or cards—enhancing code readability and aligning with web standards.

info > Should you get stuck, there is a solutions folder that can guide you in the right direction!

You'll get started by establishing the foundation for your web component suite. This step is all about creating a reusable base structure and your first component—a button—using vanilla JavaScript to keep it lightweight and portable across your projects.

You’ll leverage the Custom Elements API to register components and the Shadow DOM to isolate styles, building a button that’s both functional and visually distinct. This will be the beginning of a library that you can expand into a full UI toolkit. You’ll first define a base class for consistency and then create a button component.

A base class acts as the backbone for your web components, providing a consistent starting point for new web components. By setting up a BaseComponent with shadow DOM, you ensure all your components inherit the same structure and behavior, like a reusable template. This approach simplifies lifecycle management and keeps your code DRY (Don’t Repeat Yourself), a principle you’ve likely valued in large-scale projects.

Buttons are everywhere in UI design—making one as your first component lets you see custom elements in action fast. Defining <my-button> introduces you to customElements.define and the shadow DOM’s isolation, ensuring your styles won’t clash with other page elements.

A button needs to look the part—styling it within your shadow DOM ensures its appearance stays consistent no matter where you use it. This task showcases encapsulation’s power, keeping your styles scoped and safe from global interference, a relief if you’ve debugged style overrides before.

With your button in place, in this step you’ll make it dynamic by adding attributes like <my-button disabled>. Attributes allow you to customize your components directly in HTML, boosting reusability across different contexts, whether in React or standalone pages. This step dives into the Custom Elements lifecycle with observedAttributes and attributeChangedCallback, turning your static button into a reactive one.

In this step, you’ll define an attribute to watch and update behavior based on changes, building a component that adapts to input from the outside.

Observing attributes lets your component react to changes, a must for interactivity. This foundational task ensures your button is properly ready to listen to certain custom attributes. Now you’ll make disabled functional—toggling your button’s state ties attributes to real DOM updates. This mirrors how you’d make components responsive in production.

Now that your button is dynamic, you’ll expand your suite with a card component, introducing slots for maximum flexibility. Slots allow you to inject custom content—like text, images, or even your button—into specific parts of your component, making it a versatile container for diverse use cases.

In this step, you’ll define the card, enable slots, and nest your button inside of it. You'll even make use of slots within your my-button web component as well! The tasks in this step are a practical showcase of reusability and content projection, perfect for standalone use or integration into frameworks like React.

Cards are UI staples—think dashboards, blog posts, or product listings you’ve built. Creating a basic card component sets up a reusable layout piece, ideal for testing slots next. It’s a common pattern that shows you how web components can encapsulate structure and style cleanly.

Slots make your card a flexible shell—you can add whatever content you need, from paragraphs to buttons. This lets your component adapt to different scenarios without rewriting it.

Now it's time to validate your slot functionality, ensuring your component accepts content.

Summary of What You Learned

In this Code Lab, you’ve built a suite of reusable web components—a button and a card—using custom elements, shadow DOM, and slots. You’ve seen how attributes and lifecycle methods enhance interactivity, all within a lean, vanilla JavaScript setup.

More Advanced Web Component Topics

Ready to level up? Explore advanced topics like custom events for component communication, CSS custom properties for theming, or integrating these components into React via wrappers. Can you add an event to toggle the button’s state? Try enhancing your card with multiple named slots!

Thanks for completing this Guided Code Lab! Keep exploring web components and their potential in your projects. Check out more labs and courses on Pluralsight to deepen your skills.