open-stylable
v1.0.0
Published
Web component where styles leak in, but they don't leak out
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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-stylable
Then 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.