Import necessary styles into the shadow DOM

Question

Import necessary styles into the shadow DOM

Embracing the concept of shadow dom styles encapsulation is exciting, but I wish to incorporate base styles into each shadow dom as well (reset, typography, etc).

 <head>
 <link rel="stylesheet" href="core.css">
 ...
 </head>

 <my-component></my-component>
 <script>
   
   customElements.define('my-component', class MyComponent extends HTMLElement {
     ...
     connectedCallback() {
        this.shadow = this.attachShadow({mode: 'open'});
         const linkElem = document.createElement('link');
         linkElem.setAttribute('rel', 'stylesheet');
         linkElem.setAttribute('href', 'core.css');

         // applying existing "core.css" to current shadow dom 
         this.shadow.appendChild(linkElem);
     }
   });
 </script>

With core.css being called (linked) twice, could there be an impact on performance?

javascript html css web-component shadow-dom

Answer 1

Answer №1

If you're looking to optimize your styling approach, consider using Constructable Stylesheet Objects. By defining global styles and then incorporating them with shadowRoot.adoptedStylesheets, you can enhance the efficiency of your components:

import {
    resetSheet,
    headlinesSheet,
    coreSheet,
} from '/style-system.js';
import {
    myComponentStyles,
} from './styles.js';

// ...

connectedCallback() {
    // Only compose styles once
    if (!this.shadowRoot.adoptedStyleSheets.length) {
        this.shadowRoot.adoptedStyleSheet = [
            // global stylesheets
            resetSheet,
            headlinesSheet,
            coreSheet,
            // specific sheet for this component
            myComponentStyles
        ]
    }
}

By utilizing this method, you gain several advantages over manually linking style elements to each component:

You can share global styles across multiple components by defining them once
The component only loads the necessary styles when rendered, improving performance through lazy loading
You can dynamically modify global styles (as they are JavaScript components), simplifying updates without affecting multiple elements

To deepen your understanding of Constructable Stylesheet Objects, consider exploring the following resources:

Answer 2

If you're looking to optimize your styling approach, consider using Constructable Stylesheet Objects. By defining global styles and then incorporating them with shadowRoot.adoptedStylesheets, you can enhance the efficiency of your components:

import {
    resetSheet,
    headlinesSheet,
    coreSheet,
} from '/style-system.js';
import {
    myComponentStyles,
} from './styles.js';

// ...

connectedCallback() {
    // Only compose styles once
    if (!this.shadowRoot.adoptedStyleSheets.length) {
        this.shadowRoot.adoptedStyleSheet = [
            // global stylesheets
            resetSheet,
            headlinesSheet,
            coreSheet,
            // specific sheet for this component
            myComponentStyles
        ]
    }
}

By utilizing this method, you gain several advantages over manually linking style elements to each component:

You can share global styles across multiple components by defining them once
The component only loads the necessary styles when rendered, improving performance through lazy loading
You can dynamically modify global styles (as they are JavaScript components), simplifying updates without affecting multiple elements

To deepen your understanding of Constructable Stylesheet Objects, consider exploring the following resources:

Answer 3

Answer №2

When the browser caches the request for core.css, there is no real performance penalty. However, because the stylesheet will be loaded asynchronously, you may experience a flash of unstyled content (FOUC) as the browser retrieves the css for the first time.

To potentially avoid this issue, one solution is to preload the css file in your document within the <head> section. This way, it should (although preloads are merely 'hints' to the browser) be accessible by the time your Shadow DOM is parsed:

<link rel="preload" href="core.css" as="style">

Answer 4

When the browser caches the request for core.css, there is no real performance penalty. However, because the stylesheet will be loaded asynchronously, you may experience a flash of unstyled content (FOUC) as the browser retrieves the css for the first time.

To potentially avoid this issue, one solution is to preload the css file in your document within the <head> section. This way, it should (although preloads are merely 'hints' to the browser) be accessible by the time your Shadow DOM is parsed:

<link rel="preload" href="core.css" as="style">

Import necessary styles into the shadow DOM

Answer №1

Answer №2

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