1.11.0 • Public • Published


ShadyDOM provides a shim for ShadowDOM V1. It is less correct but less intrusive and faster than the ShadowDOM Polyfill.


Usage of the shim is transparent when attachShadow is unavailable. Elements are patched as needed to report ShadowDOM correct dom information. Only dom tree accessors and mutation api is maintained. Some dom api (for example MutationObservers) is not shimmed.

To force ShadyDOM to be used even when native ShadowDOM is available, set the ShadyDOM = {force: true} in a script prior to loading the polyfill.


<div id="host"></div>
  host.attachShadow({mode: 'open'});

Building and Testing

For building and testing, first run

npm install
npm run build

To test, run npm test


ShadyDOM distribution is asynchronous for performance reasons. This means that the composed dom will be available 1 microtask after the dom mutation occurs. For testing, ShadyDOM.flush may be called to force syncronous composition.

ShadowDOM compatible styling is not provided with the ShadyDOM shim. To shim ShadowDOM styling, use the shadycss shim.

On very old versions of Chrome and Safari, in rare cases ShadyDOM.patch(node) must be called to properly set textContent or innerHTML. On these browsers, element property accessors like firstChild and textContent cannot be modified on the element prototype and instances must be patched. This is automated but there are some cases that are not handled. This should only be an issue when setting textContent or innerHTML on a node inside a shadowRoot adds or removes a <slot> element. In this case, the shadowRoot will not render correctly. To workaround this, call ShadyDOM.patch(node) prior to setting textContent or innerHTML.

The APIs Document.querySelectorAll, Element.querySelectorAll, Node.childNodes, and ParentNode.children each return an Array instead of a NodeList or HTMLCollection.

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npm i @webcomponents/shadydom

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  • justinfagnani
  • webcomponents-devs
  • bicknellr
  • azakus
  • aomarks