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The Basics Of Creating & Using Web Components

December 20, 2023 - Adam Tulloss

Web components are a set of standardized web platform APIs that allow you to create reusable and encapsulated HTML elements with their own custom functionality. They consist of three main parts:

Custom Elements:

Custom Elements API enables developers to define their own HTML elements with a custom name and behavior. These elements can encapsulate both structure and behavior, making them reusable across different web applications.

Shadow DOM:

Shadow DOM provides a way to encapsulate the styling and behavior of a web component, preventing CSS and JavaScript from affecting or being affected by the rest of the page. This isolation ensures that components can be used without causing conflicts in larger applications.

HTML Templates:

HTML Templates allow you to declare fragments of markup that can be reused without rendering them immediately. These templates can be used within custom elements to define their structure.

Web components promote modularity and reusability in web development by allowing developers to create their own custom elements that can be easily integrated into web applications, making it easier to maintain and scale complex projects.

Two Types of Web Components

Autonomous (or Custom) Components:

Autonomous web components are standalone custom elements that do not extend existing HTML elements. They are created using the customElements.define() method and provide a new, unique HTML element with custom functionality. For example, you can define a <my-button> element with custom behavior and attributes, and then use it in your HTML like any other HTML element.

Customized Built-in Components:

Customized built-in web components, also known as “extends” components, extend existing HTML elements such as <button>, <input>, or <div>.

These components add custom functionality and styling to existing elements while inheriting their core behavior. You create them by using JavaScript classes that extend the built-in element’s prototype.

Registering A Custom Web Component

Let’s make a web component for a simple greeting, kind of like a “hello world”.

We’ll start by defining a class extending an HTMLElement, and registering it with the customElements.define function.

Next, add a constructor, where we open the shadow root and initialize the name property.

Next, complete the web component by adding the remaining necessary methods.

At this stage, you’ll notice that several things are happening. Using the shadow dom, we add an HTML template along with some styles in the render method. The render method needs to be manually called every time something changes, as well as after the web component loads.

Benefits Of Using Web Components


Web components are self-contained units that encapsulate both structure (HTML), behavior (JavaScript), and styles (CSS). This encapsulation ensures that the component’s code and styles do not interfere with other parts of the web application, reducing the risk of naming conflicts and making it easier to manage complex UI elements.


Web components are designed to be reusable. Once you’ve defined a web component, you can use it throughout your web application as many times as needed. This promotes a modular and DRY (Don’t Repeat Yourself) approach to development, saving time and effort.


Web components make use of Shadow DOM, which allows you to encapsulate the components’ styles and prevent them from affecting the global CSS of your application. This ensures that your component’s styles won’t unintentionally leak or be overridden by other styles in the project.


Web components are supported natively by all modern browsers, meaning you don’t need to rely on additional JavaScript libraries or frameworks to use them. This broad browser support makes web components a future-proof choice and ensures that your components will work consistently across different environments.


Because web components are based on web standards, they are interoperable with various JavaScript frameworks and libraries. You can use web components alongside other technologies, allowing for a gradual migration to web components or the integration of web components into existing projects.

Reduced Dependency on Frameworks:

While web components can be used with frameworks, they also provide an option for developers who prefer a lighter-weight solution without the overhead of a full-featured framework. This flexibility allows you to choose the level of complexity that best suits your project’s needs.

Ecosystem Growth:

Web components are gaining popularity, and the ecosystem around them is growing. There are libraries and tools specifically built to simplify web component development, making it increasingly convenient to create and use them in your projects.

Web Components As a Compilation Target

Web components can serve as a compilation target for various JavaScript frameworks and libraries. This means that you can write your application using a particular framework or library and then compile it into web components, which are standards-based and can be used in different contexts without depending on the original framework. This approach offers several benefits:


Compiled web components can be used in applications built with different frameworks or vanilla JavaScript, promoting component reuse across projects and ecosystems.


Web components encapsulate their functionality, styles, and templates, preventing them from interfering with the global scope or other parts of the application.


By compiling web components, you ensure that your components remain compatible with evolving web standards and technologies.

Lit Frameworks:

Frameworks like Lit are specifically designed to simplify the creation and management of web components. Lit offers a lightweight and developer-friendly approach to building web components by providing a set of tools and patterns.

Key Features Of Lit Include:

Template Literals:

Lit uses JavaScript template literals to define component templates, making it easier to work with HTML and JavaScript together.

Reactive Data Binding:

Lit provides a simple way to establish data binding between JavaScript properties and DOM elements, allowing components to update when data changes reactively.

Efficient Updates:

Lit optimizes updates by only modifying the parts of the DOM that need to change, improving performance.

Component Composition:

Lit supports composing components, making it easy to build complex applications from smaller, reusable pieces.

Svelte Frameworks

Svelte is a different approach to web development where components are compiled directly to highly efficient JavaScript code. While Svelte is not exclusively designed for web components, it can compile components into web components, making them reusable and interoperable.

Key Aspects Of Svelte Include:

Compile-Time Framework:

Svelte shifts much of the framework logic to compile time, resulting in smaller and faster output code.


Svelte encourages a component-based approach to UI development, and these components can be compiled into web components for use in various contexts.

Automatic Reactivity:

Svelte automatically adds reactivity to components, making it easy to create responsive user interfaces.

Small Bundle Size:

The compiled output from Svelte is typically smaller compared to traditional frameworks, leading to faster load times.

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