Definition
HTML Standard defines CustomElementRegistry
[Exposed=Window]
interface CustomElementRegistry {
[CEReactions] undefined define(DOMString name, CustomElementConstructor constructor, optional ElementDefinitionOptions options = {});
(CustomElementConstructor or undefined) get(DOMString name);
DOMString? getName(CustomElementConstructor constructor);
Promise<CustomElementConstructor> whenDefined(DOMString name);
[CEReactions] undefined upgrade(Node root);
};