Declarative Shadow DOM
Attach shadow DOM from HTML without JavaScript using shadowrootmode.
The Problem It Solves
Traditional Shadow DOM is created via JavaScript (attachShadow). For server-rendered pages, this means the shadow tree is empty until JS runs — defeating SSR's purpose of delivering complete HTML on first byte. Declarative Shadow DOM fixes this.
The shadowrootmode Attribute
A <template> with shadowrootmode="open" declares a shadow root in HTML at parse time. The browser attaches the shadow root to the parent element automatically; the template's content becomes the shadow tree. No JavaScript required.
<my-card>
<template shadowrootmode="open">
<style>:host { display: block; padding: 16px; }</style>
<slot></slot>
</template>
<p>This goes into the slot</p>
</my-card>All lessons in this course
- Declarative Shadow DOM
- The Popover API
- The selectlist Element
- Interest Invokers and Command Attribute