what polyfills are you talking about? And no, Polymer is not a polyfill for custom element. Please link me to a library that will polyfill the entire shadow DOM and Custom Element spec so that I can write the same code without polyfills on platforms that support both specs and only load the polyfills on platforms that do not.

https://github.com/vuejs/vue-web-component-wrapper

"You will also need the Shady DOM + Custom Elements polyfill." from Vue docs. Same polyfills are used by svelte etc.

Quote from the readme.

" A suite of polyfills supporting the Web Components specs:

Custom Elements v1: allows authors to define their own custom tags (spec, tutorial, polyfill).

Shadow DOM v1: provides encapsulation by hiding DOM subtrees under shadow roots (spec, tutorial, shadydom polyfill, shadycss polyfill). "