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Declarative Shadow Root (DSR) <shadow-root>

Build Status

This is a protoype repository to test and showcase the functionality and needs of a declarative shadow DOM approach discussed at GitHub. It's coherent with my master thesis: "Application of a Declarative Shadow DOM for the Definition of Web Components"

Chrome will already ship this feature in Chrome 90 driven by Mason Freed https://www.chromestatus.com/feature/5191745052606464

Abstract

Web Components complement client-side web development with a native component model. However, as of today, the interest in adopting the web standard is still limited because of disadvantages such as server-side rendering. The idea of it is nothing new, but it has been said that Web Components can not be rendered on the server due to the lack of a declarative representation of a shadow DOM. The purpose of a declarative approach is to empower non-scripting environments with the features Web Components provide, especially the encapsulation aspect of the shadow DOM. This would also enhance serverside pre-rendering ofWeb Components and additionally push the adoption of this feature further among the web community. A declarative shadow root can potentially establish a new way of attaching a shadow DOM additionally to the imperative way. The goal is not to replace the current mechanism, but to expand the use cases of the shadow DOM.

The original proposal of a declarative shadow DOM was declined in 2019 by browser vendors and web specification developers due to implementation costs. The main aim of this thesis is to create a reasonable prototype, point out the advantages and disadvantages of a declarative approach as well as provide reasons to reconsider developing it.

TL;DR

DSD is effectively just a declarative form of .attachShadow(...) with a couple tweaks to make it work nicely with existing .attachShadow calls.

Installation

npm i

Usage

<my-test id="shadow-host">
  <shadow-root mode="open | closed">
    <h2>Shadow h2</h2>
    <slot></slot>
    <div>Shadow div</div>
  </shadow-root>
  <div>Light content</div>
</my-test>

<script type="module">
  import 'shadow-root.js';
</script>

Folder structure

  • demo - the demo files are located here
    • performance -- a HTML file containing a lot of shadow-root elements
    • profile -- an example how to utilise the element for a profile-card
    • index.html -- the demo playground where you can test and expirement with the element freely
  • perf - the performance benchmark using tachometer
  • src - the source files for the DSR element
    • declarative-shadow-dom.js -- a third party solution employing a template element
    • index.js -- registering all custom elements for easier access
    • OrdinaryComponent.js -- an ordinary Web Component to test use cases combined with a DSR
  • test - the unit tests which are run by the travis CI. Using @open-wc/testing

Running

Local Demo with es-dev-server

To run a local development server that serves the basic demo located in demo/index.html:

npm start

Testing (with Karma)

I've used the open-wc for Web Component testing.

To run the suite of karma tests:

npm run test

To run the tests in watch mode:

npm run test:watch

To run the tests with coverage check:

npm run test:coverage

Testing via BrowserStack

To run the suite of karma tests in BrowserStack, run

npm run test:bs

Managing Test Snapshots

You can manage the test snapshots using

npm run test:update-snapshots

or

npm run test:prune-snapshots