open-stylable
v1.0.0
Published
Web component where styles leak in, but they don't leak out
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nolanlawsonReadme
open-stylable
Tiny (<0.5kB min+gz) proof-of-concept implementation of an "open-stylable" web component. It can be styled from the global <head>, even though it uses shadow DOM.
So basically: styles leak in, but they don't leak out.
<head>
<style>div { color: red }</style>
</head>
<body>
<my-component>
#shadow-root
<div>I'm red!</div>
</my-component>
</body>Usage
Install:
npm install open-stylableThen use as a mixin:
import { OpenStylable } from 'open-stylable'
class MyComponent extends OpenStylable(HTMLElement) {
constructor() {
super()
this.attachShadow({ mode: 'open' }).innerHTML = '<div>Hello world</div>'
}
}This custom element will use shadow DOM, but any styles from the <head> will be copied into its shadow root.
connectedCallback and disconnectedCallback
If you use connectedCallback or disconnectedCallback, be sure to call super:
class MyComponent extends OpenStylable(HTMLElement) {
connectedCallback() {
super.connectedCallback()
/* Your code */
}
disconnectedCallback() {
super.disconnectedCallback()
/* Your code */
}
}In a framework
The OpenStylable mixin allows you to use whatever constructor you like. For instance, with a Lit component:
class MyComponent extends OpenStylable(LitElement) {
/* ... */
}Limitations
This only works with open shadow DOM, not closed shadow DOM.
Also, it doesn't work with selectors that cross shadow boundaries, such as body.foo *.
Additionally, it only works for <style> and <link rel="stylesheet"> tags in the <head>. More exotic ways of inserting styles, such as insertRule and document.adoptedStyleSheets, are not supported.
Although it would be possible to support such things, it would increase the bundle size and require global patching, which is a big cost for a niche feature.
This implementation also uses MutationObserver, which may have performance considerations if you have a lot of components and frequently-changing global styles.