Scoped CustomElementRegistry polyfill prototype
🚨 Work in progress
This polyfill explores implementation of a non-finalized spec proposal and is currently a work in progress.
Overview
Scoped CustomElementRegistry polyfill based on Scoped Custom Element Registries WICG proposal.
Technique: uses native CustomElements to register stand-in classes that
delegate to the constructor in the registry for the element's scope; this
avoids any manual treewalks to identify custom elements that need upgrading.
Constructor delegation is achieved by constructing a bare HTMLElement
,
inspecting its tree scope (or the tree scope of the node it was created via) to
determine its registry, and then applying the "constructor call trick" to
upgrade it.
Notes/limitations:
- In order to leverage native CE when available,
observedAttributes
handling must be simulated by patchingsetAttribute
/getAttribute
/toggleAttribute
to callattributeChangedCallback
manually, since while we can delegate constructors, theobservedAttributes
respected by the browser are fixed at define time. This means that native reflecting properties are not observable when set via properties. - In theory, this should be able to be layered on top of the Custom Elements
polyfill for use on older browsers, although this is yet to be tested. Use of
Reflect.construct
may need to be modified in those cases
Outstanding TODOs: