HTML Imports

HTML Imports was a feature introduced as part of the Web Components standard, allowing the reuse of HTML documents across multiple pages by importing them into other HTML files. This feature aimed to modularize web development, making it easier to reuse and manage code. However, HTML Imports were later deprecated in favor of more modern technologies like ES6 modules and JavaScript frameworks that provide similar functionality.

In this chapter, we’ll explore the concept of HTML Imports from basic to advanced, understanding its purpose, usage, and alternatives in current web development practices. We will also provide examples to demonstrate how HTML Imports worked and what can be used instead in today’s web development environment.

What are HTML Imports?

HTML Imports allowed developers to include external HTML documents within another HTML file. This meant you could package reusable components like navigation bars, footers, or any other piece of HTML and easily import them across multiple pages. The key benefit of this was code reuse and easier maintenance.

Syntax

				
					<link rel="import" href="component.html">
  • rel="import" specifies that this is an HTML Import.
  • href points to the external HTML file that you want to import.

Once the external HTML file is imported, its content could be accessed via JavaScript and inserted into the document.

Basic Example of HTML Imports

Let’s see a basic example of how HTML Imports worked.

component.html

				
					<div class="header">
  <h1>This is the imported header</h1>
</div>

index.html

				
					<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>HTML Imports Example</title>
  <link rel="import" href="component.html">
</head>
<body>
  <h2>Main Page Content</h2> <script type="litespeed/javascript">var link=document.querySelector('link[rel="import"]');var content=link.import;var header=content.querySelector('.header');document.body.appendChild(header.cloneNode(!0))</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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</html>

Explanation

  • The component.html file contains a simple HTML structure representing a header.
  • The index.html file imports component.html using the <link> element with rel="import".
  • In the <script> section, the JavaScript code selects the imported content and appends it to the main document’s body.
  • The cloneNode(true) method ensures that the imported content is a copy that can be inserted into the DOM.

Output

When you open index.html, it will display:

				
					Main Page Content
This is the imported header

The header content from component.html is dynamically injected into index.html.

Why Were HTML Imports Deprecated?

HTML Imports were part of an effort to introduce a more modular approach to web development. However, they were eventually deprecated and replaced by more versatile and robust alternatives, primarily because:

  • Browser Support: HTML Imports had limited support and were never widely adopted across major browsers like Firefox and Edge.
  • Standardization Issues: There were concerns about the performance and complexity of HTML Imports compared to other modern approaches like ES6 modules.
  • Better Alternatives: JavaScript ES6 modules and frameworks like React, Angular, and Vue.js emerged, offering better solutions for modular web development, including reusability, componentization, and encapsulation.

Due to these reasons, the Web Components standard shifted towards a more JavaScript-centric approach, and HTML Imports were officially deprecated in 2019.

Alternatives to HTML Imports

Although HTML Imports were deprecated, modern web development provides several alternatives to achieve the same goal of modular and reusable components. Some of the popular alternatives include:

JavaScript ES6 Modules

ES6 modules allow you to split your JavaScript code into reusable pieces that can be imported and exported between files. This is a robust way to structure and modularize your code.

Example

				
					 <script type="module">import { myComponent } from './component.js';
  
  // Use the imported component
  document.body.appendChild(myComponent());</script>

component.js:

				
					export function myComponent() {
  const div = document.createElement('div');
  div.innerHTML = '<h1>This is a component</h1>';
  return div;
}

Explanation

  • component.js exports a function that creates a reusable HTML component.
  • In the main HTML file, this component is imported and appended to the body.
  • This approach provides full support across modern browsers and allows the use of JavaScript to create and manage dynamic content.

Web Components

Web Components provide a native way to create reusable and encapsulated custom elements in HTML. They consist of three main technologies: Custom Elements, Shadow DOM, and HTML Templates.

Example

				
					<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Web Components Example</title>
</head>
<body>
  <my-header></my-header> <script type="litespeed/javascript">class MyHeader extends HTMLElement{constructor(){super();this.innerHTML=`
          <header>
            <h1>This is a reusable header component</h1>
          </header>
        `}}
customElements.define('my-header',MyHeader)</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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</html>

Explanation

  • The custom element <my-header> is defined using JavaScript.
  • This reusable component can be used across multiple HTML pages, just like HTML Imports but with better encapsulation and browser support.
  • The content is added within the constructor of the class MyHeader, which extends the HTMLElement.

HTML Templates as a Replacement for Imports

Another part of the Web Components specification is the <template> element, which allows you to define chunks of HTML that can be reused later in the document.

Example

				
					<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>HTML Template Example</title>
</head>
<body>
  <h2>Main Content</h2>

  <template id="header-template">
    <div class="header">
      <h1>This is a header from the template</h1>
    </div>
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Delayed"),litespeed_ui_events.forEach(e=>{window.removeEventListener(e,litespeed_load_delayed_js_force,{passive:!0})}),document.querySelectorAll("iframe[data-litespeed-src]").forEach(e=>{e.setAttribute("src",e.getAttribute("data-litespeed-src"))}),"loading"==document.readyState?window.addEventListener("DOMContentLoaded",litespeed_load_delayed_js):litespeed_load_delayed_js()}litespeed_ui_events.forEach(e=>{window.addEventListener(e,litespeed_load_delayed_js_force,{passive:!0})});async function litespeed_load_delayed_js(){let t=[];for(var d in document.querySelectorAll('script[type="litespeed/javascript"]').forEach(e=>{t.push(e)}),t)await new Promise(e=>litespeed_load_one(t[d],e));document.dispatchEvent(new Event("DOMContentLiteSpeedLoaded")),window.dispatchEvent(new Event("DOMContentLiteSpeedLoaded"))}function litespeed_load_one(t,e){console.log("[LiteSpeed] Load ",t);var 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 <template> element defines HTML that is not rendered when the page initially loads.
  • JavaScript is used to select the template, clone it, and insert it into the document.
  • This approach is similar to HTML Imports but leverages modern JavaScript and provides more flexibility.

Although HTML Imports were once seen as a promising solution for reusing components and modularizing web pages, they have been deprecated due to limited browser support and the emergence of better alternatives. Today, web developers rely on ES6 modules, Web Components, and JavaScript frameworks to achieve similar, if not better, functionality. Happy coding !❤️

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