ShadowRoot: serializable property

The serializable read-only property of the ShadowRoot interface returns true if the shadow root is serializable.

If set, the shadow root may be serialized by calling the Element.getHTML() or ShadowRoot.getHTML() methods with the options.serializableShadowRoots parameter set true.

The serializable property of a shadow root is specified when the shadow root is created, either declaratively by adding the shadowrootserializable attribute on a <template> element (along with an allowed shadowrootmode value), or by setting the options.serializable parameter to true when using Element.attachShadow().

let customElem = document.querySelector("my-shadow-dom-element");
let shadow = customElem.shadowRoot;

// ...

// Is it serializable?
let hostElem = shadow.serializable;