Blazor Shadow DOM

A modified version of Microsoft's Blazor JavaScript files to add support for shadow DOMs.

Development and testing happens in https://github.com/ostomachion/aspnetcore

Still in development, but mostly tested and functional for Blazor WebAssembly projects.

Also see Blazor Web Components for a library that turns Blazor components into real standards-based Web Components using custom elements, shadow DOM, and HTML templates.

Installation

dotnet add package Ostomachion.Blazor.V7_0_3.ShadowDom --version 1.0.0-preview2

Important: Make sure that the package you download matches the version of ASP.NET Core that you are using. Currently only 7.0.3 is supported. Other versions are coming soon!

Setup

WebAssembly

In wwwroot/index.html, replace the Blazor script

<script src="_framework/blazor.webassembly.js"></script>

with the Blazor Shadow DOM script

<script src="_content/Ostomachion.Blazor.V7_0_3.ShadowDom/blazor.webassembly.js"></script>

Server

In Pages/_Host.html, replace the Blazor script

<script src="_framework/blazor.server.js"></script>

with the Blazor Shadow DOM script

<script src="_content/Ostomachion.Blazor.V7_0_3.ShadowDom/blazor.server.js"></script>

MAUI / WebView

In wwwroot/index.html, replace the Blazor script

<script src="_framework/blazor.webview.js" autostart="false"></script>

with the Blazor Shadow DOM script

<script src="_content/Ostomachion.Blazor.V7_0_3.ShadowDom/blazor.webview.js" autostart="false"></script>

Usage

The new scripts modify the Blazor renderer to recognize declarative shadow DOMs. In a .razor file, you can add a template element with a shadowrootmode attribute to get Blazor to attach a shadow root to the parent element.

<div id="host">
  <template shadowrootmode="open">
    <p>Shadow Content</p>
    <slot></slot>
  </template>
  <p>Light content</p>
</div>

This script was written to follow the declarative shadow DOM spec as closely as possible, so a normal template element will be rendered if the parent element cannot be a shadow host. Likewise, if the component does not define a parent for the template element, a normal template will be rendered no matter what the actual parent is at runtime.