Polyfills and Shims
Scripts adding partial support for stable and experimental web components features.
Constructible style sheets polyfill
A polyfill for the constructible style sheets / adopted style sheets spec.
Custom Elements HMR Polyfill
100% standard-compliant polyfill to allow Web Component re-definition at runtime (used for HMR).
Custom Elements Polyfill
Custom Elements polyfill including the ability to extend builtin elements.
Declarative Shadow DOM Ponyfill
A ponyfill that allows HTML with shadow roots to be serialized to plain HTML.
Element Internals Polyfill
A polyfill for the ElementInternals interface (part of HTML standard).
ES Module Shims
CSS Modules need to be manually enabled via the polyfillEnable init option.
Manage loading polyfills and/or serving different versions of your application based on browser support.
Experimental Lit mixin to support using multiple different versions of the same web component on the page.
Shadow Container Query Polyfill
Fork of Container Query polyfill by GoogleChromeLabs with some tweaks adding support for Shadow DOM.
A ponyfill for the TemplateInstance API, part of the Template Parts proposal.
Web Components Polyfills