Customizing native HTML elements with JavaScript

Anton Ioffe - November 6th 2023 - 8 minutes read

In the ever-evolving landscape of web development, harnessing the power of JavaScript to customize native HTML elements has become a core aspect of delivering dynamic and user-friendly web interfaces. This article delves deep into the art and science of augmenting native HTML elements using JavaScript, offering practical insights, robust use-cases, and addressing commonplace mistakes. We will also explore how web components can aid in the customization process while uncovering the best practices to ensure optimal performance. From rudimentary understandings to advanced concepts, this article promises a comprehensive guide that will deepen your mastery over customizing HTML elements - a skill that, once honed, can drastically elevate the caliber of your web applications.

Understanding the Basics of Customizing Native HTML Elements

HTML's power in structuring web applications is well-established. Despite its strengths, HTML lacks flexibility. This limitation manifests prominently in HTML's fixed vocabulary and limited extensibility. Enter the concept of custom elements. These provide an essential approach towards the modernization of HTML. They extend HTML's capabilities, rectify its shortcomings, and enable a cohesive blend of structure with behavior. In practical terms, custom elements facilitate the definition of new HTML tags, augmentation of existing ones, and the creation of reusable components using nothing more than vanilla JavaScript. The result is less code to maintain, improved code modularity, and greater reusability across your applications.

Customized built-in elements constitute a particularly interesting subset of custom elements. They are essentially custom elements that inherit the functionalities of built-in HTML tags. This confers the dual advantages of utilizing the built-in tag's core features (e.g., properties, methods, and accessibility) and simultaneously adding new behaviors. It embodies the essence of progressive enhancement, taking existing HTML elements and building upon them. An illustrative example of this would be extending the native anchor element (<a>). Through this customization, we can intercept the click event and introduce a confirm prompt to ensure the user is certain about navigation.

In order to develop these customized built-in elements, we use JavaScript's customElements global object. This object offers us the define() method, which we use to register a new custom element in the CustomElementRegistry. However, when extending a built-in HTML tag, the syntax is slightly different:

class ExtendedAnchor extends HTMLAnchorElement {
    // Your unique functionality here
customElements.define('extended-anchor', ExtendedAnchor, { extends: 'a' });

In this example, the third parameter in the define() method configures the extending of the <a> tag, effectively creating a new anchor element with additional behaviors.

So, when talk about extending native HTML elements, it encompasses redefining and mutating the behaviors of these elements while preserving the native behaviors that come built-in. In the world of web development, this offers an unprecedented balance by maintaining the familiarity of existing elements while providing the flexibility to introduce custom behaviors, significantly improving the user engagement and overall web usability. The guiding principle is always to enhance elements in a way that improves the interactivity and functionality of web pages while ensuring a commitment to accessibility standards.

Customizing Native Element Behavior with JavaScript

In approaching the task of customizing native HTML elements, JavaScript provides a valuable toolset that can enhance the behavior of these foundational structures. Taking the example of the standard HTML link element (<a>), when you are working with multiple links that require navigation confirmation, JavaScript aids in redefining this behavior without the need to create individual code for each tag. Here's an example:

class ConfirmLink extends HTMLAnchorElement {
    constructor() {
        this.addEventListener('click', (event) => {
            if (!confirm('Are you sure you want to navigate?')) {
customElements.define('confirm-link', ConfirmLink, { extends: 'a' });

In this concise piece of code, the ConfirmLink class has been sculpted from HTMLAnchorElement, whereby 'click' events are intercepted to request user confirmation.

Transitioning our focus to the dropdown (<select>), it can also be visually enhanced and made more adaptable with the help of JavaScript. By defining a class extending HTMLElement and injecting it with necessary properties or methods, such a task can be performed. A prototype might look like this:

class CustomSelect extends HTMLElement {
    constructor() {
        // Initialize your custom select components
    populateDropdown(optionsList) {
        optionsList.forEach((option) => {
            let selectOption = document.createElement('option');
            selectOption.text = option;
window.customElements.define('custom-select', CustomSelect);

In this process, it's important to make sure to keep up the aspects that you appreciate in native elements, such as accessibility, default functionality, and levels of familiarity.

Furthermore, when it comes to elements like <button> and <img>, these extend not from HTMLElement, but rather from HTMLButtonElement and HTMLImageElement respectively. This is notable because it ensures that your custom element retains the original features and behaviors of these key elements.

class CustomButton extends HTMLButtonElement {
    // Add your custom behaviors. For example:
    connectedCallback() {
        this.addEventListener('click', () => {
   = 'red'; // Change color upon button click
window.customElements.define('custom-button', CustomButton, { extends: 'button' });

With this understanding of how JavaScript can be used to augment native HTML elements, you can confidently create unique and highly functional components. Whether you want to adapt existing behaviors or develop something entirely new, JavaScript supports you in the endeavor to write efficient and effective code.

Leveraging Web Components to Customize HTML Elements

Custom elements facilitate the enhancement of native HTML tags, laying the foundation for integrated, structured components, and streamlining code into manageable, reusable units. Suppose there is a need for a user interface component that goes beyond the capabilities of standard HTML tags and mandates specific behaviors. In such a scenario, custom elements empower you to define a novel HTML tag, encapsulating these unique functionalities.

// Extend HTMLElement
class CustomParagraph extends HTMLElement {
  constructor() {

    // Attach the shadow DOM to use for encapsulation
    const shadow = this.attachShadow({mode: 'open'});

    // Create a paragraph element
    const p = document.createElement('p');

    // Add text content
    p.textContent = 'This is a custom paragraph!';

    // Append 'p' to the shadow root

// Define the new custom element
customElements.define('custom-paragraph', CustomParagraph);

The Shadow DOM further enriches modern web development by providing an isolated space, ensuring that your components' style and behavior remain impervious and unmodified within the Document Object Model. It guarantees that style and scripts confined within this shadow boundary do not leak into the surrounding code, and vice versa.

HTML's template is another potent tool in our array to boost web components. It allows encapsulation of reusable DOM fragments, proving extremely practical when creating intricate components requiring elaborate HTML structures, thereby adhering to the DRY (Don't Repeat Yourself) principle.

However, the use of web components and customized HTML elements isn't without its challenges. They are still only natively supported in modern browsers, which might lead to compatibility issues with older versions. Moreover, the learning curve might be relatively steep for developers new to these concepts, potentially causing project delays. Performance-wise, while component-level encapsulation aids in better manageability and debugging, the shadow DOM may introduce slight overhead due to encapsulation and style confinement.

From a perspective of memory management, web components may result in higher usage if not handled properly, especially in large-scale applications. Have you considered the memory impact of your current project's code? That said, these challenges can usually be overcome with careful planning, making web components a potential game-changer in customizing HTML elements.

Bringing it full circle, the question to ponder is: Given their pros and cons, and considering their performance and memory implications, are web components the optimal approach when customizing HTML elements in your next web development project?

Common Mistakes and Best Practices

One common mistake developers often make involves adding new elements to a web page, which reflows the content and impacts performance. This occurs when the browser recalculates dimensions, positioning, layouts, and attributes of elements related to the injected element. This operation is expensive in terms of computational resources, and the issue compounds with each added element. Particularly in single-page applications, which might not reset the DOM between transitions, the page could end up with hundreds of injected elements, each harming performance incrementally. The correct alternative, unless absolutely necessary, is to avoid injecting new elements to the HTML page.

On the topic of custom HTML tags, developers commonly fall into the pitfall of overuse. While certainly a powerful feature, it's important to exercise restraint. One erroneous practice is the flippant injection of Custom HTML tags, which by default are added to the end of the <body>. This disregard for careful placement can lead to visual components appearing out of order or in unexpected positions on the screen. To avoid this, best practice involves careful strategic positioning, using JavaScript's DOM manipulation methods to place new elements relative to existing ones.

When creating new custom elements from scratch, a classic mistake is to sacrifice functionality for aesthetic reasons. This mistake commonly appears when we create a custom dropdown using the <select> element. Although a custom dropdown can be visually pleasing, we force users to interact with it in a specific manner that may not be expected. Unexpected interaction models can lead to confusing user experiences. As a best practice, developers should build 'hybrid' components that prioritize functionality over aesthetics, maintaining accessibility advantages inherent with native elements.

Lastly, it's important to note a misstep many developers make due to eagerness or expediency - not considering the deviations in behavior of native elements across different browsers and screen readers. A custom dropdown that works seamlessly in Firefox might not perform identically in Safari or Internet Explorer. The solution to this common mistake is meticulous testing on multiple platforms, browsers and devices to ensure a consistent cross-platform behavior. Best practice advocates for a prophylactic approach - anticipate problems beforehand and develop solutions to these potential issues ahead of time.

Advanced Concepts and Use Cases

One radical aspect of using custom elements with JavaScript is the ability to extend the native HTML elements. Consider a scenario where we are aiming to create a progressive enhancement. Rather than producing an entirely new element, we can deliberately extend the existing one and subsequently inherit from the appropriate DOM interface.

A good example of this are elements like <button> or <img>, where they should inherit from HTMLButtonElement or HTMLImageElement respectively. Thus, these custom elements will retain the original features and behaviors of these core elements. For example, we could have a CustomButton class that extends the HTMLButtonElement and adjusts the color each time the button is clicked. Here’s a commented code example:

class CustomButton extends HTMLButtonElement {
    constructor() {
        // inherits the properties and methods of the HTMLButtonElement interface

    connectedCallback() {
        this.addEventListener('click', () => = 'red');
        // changes the color of the button text to red on clicking

customElements.define('custom-button', CustomButton, { extends: 'button' });
// The third argument specifies the built-in element your element extends.

However, building truly accessible custom components, such as a dropdown, is harder than you'd think. WCAG offers excellent guidance with its best practices, but the support for ARIA is tepid and different browsers interpret native <select> elements in various manners. This means that despite creating a unique user experience with your custom HTML elements, also maintaining full accessibility can be a daunting task.

So, how does this shape the future of web development? Will extending native HTML elements become commonplace, or will it remain a niche practice for bespoke use cases? Can we evolve beyond the need for such methods as the web components holy grail? These are the thought-provoking questions to ponder upon as we embrace custom elements to redefine web development paradigms.


In this article, the author explores the concept of customizing native HTML elements using JavaScript in modern web development. They discuss the basics of custom elements, provide examples of extending native HTML tags, and explain how web components can be leveraged for customization. The article also highlights common mistakes and best practices to consider when customizing HTML elements. The key takeaway from this article is that JavaScript offers a powerful toolset for enhancing the behavior and functionality of HTML elements, allowing developers to create unique and highly functional components. A challenging task for the reader to further enhance their understanding of JavaScript and customizing HTML elements would be to create their own custom element by extending a built-in HTML tag and adding their own functionality to it, exploring the possibilities and limitations of customizing native elements with JavaScript.

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