HTML Web components

Web components are a powerful feature in modern HTML that allow developers to create reusable and encapsulated custom elements. These components work independently from the rest of the document and can be reused in various parts of a web application. They provide a structured way to build complex web applications by separating concerns and enhancing code maintainability. This chapter delves into the concept of web components in HTML, exploring the basics to advanced concepts with examples, and demonstrating how to implement them effectively.

What are HTML Web Components?

HTML Web Components are a set of technologies that allow developers to create reusable and encapsulated custom elements. They help developers build widgets or components like buttons, sliders, modals, and more that can be easily reused across different parts of an application or even in different projects.

Key technologies in Web Components:

  1. Custom Elements: Create custom HTML tags.
  2. Shadow DOM: Encapsulates the component’s structure and style, preventing it from affecting the rest of the document.
  3. HTML Templates: Defines markup templates that are not rendered until explicitly used.

Why Use Web Components?

Web components offer several advantages:

  • Reusability: Components can be created once and reused across the web application.
  • Encapsulation: Components are isolated, preventing styles and scripts from affecting other elements.
  • Maintainability: Components break down a complex UI into smaller, manageable pieces.
  • Compatibility: Once created, web components can be used in different projects without modification.

The Core Technologies Behind Web Components

Custom Elements

Custom Elements allow developers to create new HTML tags or extend existing ones.

Example

				
					<!DOCTYPE html>
<html lang="en">
<head>
    <title>Custom Elements Example</title>
</head>
<body>
    <user-card></user-card> <script type="litespeed/javascript">class UserCard extends HTMLElement{constructor(){super();this.innerHTML=`<h2>User: John Doe</h2>`}}
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</html>

Explanation

  • The code defines a new element <user-card> using the UserCard class, which extends the HTMLElement class.
  • The customElements.define method registers the custom element. Now, you can use <user-card> just like any HTML tag.

Output: The page displays “User: John Doe” within the custom element <user-card>.

Shadow DOM

The Shadow DOM allows you to create an isolated component where styles and scripts do not leak to or from the outer DOM.

Example

				
					<!DOCTYPE html>
<html lang="en">
<head><style>h2 {
            color: red;
        }</style><title>Shadow DOM Example</title>
</head>
<body>
    <user-card></user-card> <script type="litespeed/javascript">class UserCard extends HTMLElement{constructor(){super();const shadow=this.attachShadow({mode:'open'});shadow.innerHTML=`
                    <style>
                        h2 { color: blue; }
                    </style>
                    <h2>Shadow DOM User: Jane Doe</h2>
                `}}
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</html>

Explanation

  • Here, we use this.attachShadow({ mode: 'open' }) to create a shadow DOM.
  • The <style> inside the shadow DOM applies only to the contents of the shadow DOM and does not affect the rest of the document.

Output: The heading inside the shadow DOM is blue, while any other <h2> elements outside the shadow DOM will be red.

HTML Templates

The <template> element is used to define a block of HTML that is not rendered immediately. Instead, it can be cloned and attached to the DOM later.

Example

				
					<!DOCTYPE html>
<html lang="en">
<head>
    <title>HTML Template Example</title>
</head>
<body>
    <template id="my-template">
        <h2>Template User: Jane Smith</h2>
    </template>

    <user-card></user-card> <script type="litespeed/javascript">class UserCard extends HTMLElement{constructor(){super();const template=document.getElementById('my-template').content.cloneNode(!0);this.attachShadow({mode:'open'}).appendChild(template)}}
customElements.define('user-card',UserCard)</script> <script data-no-optimize="1">!function(t,e){"object"==typeof exports&&"undefined"!=typeof module?module.exports=e():"function"==typeof define&&define.amd?define(e):(t="undefined"!=typeof globalThis?globalThis:t||self).LazyLoad=e()}(this,function(){"use strict";function e(){return(e=Object.assign||function(t){for(var e=1;e<arguments.length;e++){var n,a=arguments[e];for(n in a)Object.prototype.hasOwnProperty.call(a,n)&&(t[n]=a[n])}return t}).apply(this,arguments)}function i(t){return e({},it,t)}function o(t,e){var n,a="LazyLoad::Initialized",i=new t(e);try{n=new CustomEvent(a,{detail:{instance:i}})}catch(t){(n=document.createEvent("CustomEvent")).initCustomEvent(a,!1,!1,{instance:i})}window.dispatchEvent(n)}function l(t,e){return t.getAttribute(gt+e)}function c(t){return l(t,bt)}function s(t,e){return function(t,e,n){e=gt+e;null!==n?t.setAttribute(e,n):t.removeAttribute(e)}(t,bt,e)}function r(t){return s(t,null),0}function u(t){return null===c(t)}function d(t){return c(t)===vt}function f(t,e,n,a){t&&(void 0===a?void 0===n?t(e):t(e,n):t(e,n,a))}function _(t,e){nt?t.classList.add(e):t.className+=(t.className?" 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d=document.createElement("script");d.addEventListener("load",e),d.addEventListener("error",e),t.getAttributeNames().forEach(e=>{"type"!=e&&d.setAttribute("data-src"==e?"src":e,t.getAttribute(e))});let a=!(d.type="text/javascript");!d.src&&t.textContent&&(d.src=litespeed_inline2src(t.textContent),a=!0),t.after(d),t.remove(),a&&e()}function litespeed_inline2src(t){try{var d=urlCreator.createObjectURL(new Blob([t.replace(/^(?:<!--)?(.*?)(?:-->)?$/gm,"$1")],{type:"text/javascript"}))}catch(e){d="data:text/javascript;base64,"+btoa(t.replace(/^(?:<!--)?(.*?)(?:-->)?$/gm,"$1"))}return d}</script></body>
</html>

Explanation

  • The content inside the <template> tag is not rendered until explicitly inserted into the DOM using cloneNode(true).
  • This allows you to reuse template content multiple times across your application.

Output: The text “Template User: Jane Smith” appears within the custom <user-card> element.

Building a Complex Web Component

Let’s create a more advanced web component: a custom <product-card> that displays a product’s details and an image.

Example

				
					<!DOCTYPE html>
<html lang="en">
<head>
    <title>Product Card Component</title>
</head>
<body>
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</html>

Explanation

  • We created a product card with an image, a title, and a price.
  • The shadow.innerHTML contains both styles and the structure of the card. The CSS ensures the card is styled with padding and a border.

Output: The browser displays a neatly styled product card with a placeholder image, product name, and price.

Web components allow developers to build reusable, encapsulated, and independent elements in HTML. By leveraging custom elements, shadow DOM, and HTML templates, web applications can be made more modular and maintainable. These components help keep code clean and efficient, especially in large-scale projects. Happy coding !❤️

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