`<selectlist>` polyfill

Based on the proposal open-ui.org/components/selectmenu by Open UI.

This polyfill depends on the Popover API and comes with a light popover polyfill built-in. So it doesn't require the Popover polyfill but aims to be compatible if you wish to use these together.

One of the goals was to research and create it as closely to spec as possible and use the learnings for the implementation in Media Chrome.

Usage Codesandbox

Until the native <selectlist> lands in one of the browsers it's recommended to use the custom elements <x-selectlist> and <x-option> directly and not use them as a polyfill.

This is to prevent breaking anything in the future if the native <selectlist> API would change and you would be running a native selectlist and a polyfilled selectlist with misaligned API's.

<script type="module" src="https://cdn.jsdelivr.net/npm/selectlist-polyfill/src/selectlist.min.js"></script>
<script type="module" src="https://cdn.jsdelivr.net/npm/selectlist-polyfill/src/option.min.js"></script>

<x-selectlist>
  <x-option>Option 1</x-option>
  <x-option>Option 2</x-option>
  <x-option>Option 3</x-option>
</x-selectlist>

See all examples

Caveats

Firefox and Safari don't allow creating a shadow DOM
on custom tags like selectlist so the polyfill replaces selectlist elements
with x-selectlist elements via a mutation observer. If you prefer your elements
are not replaced use x-selectlist directly.
Safari doesn't render <option> content not nested in <select> so option
elements nested under x-selectlist are automatically replaced with x-option
elements. Again if you prefer to keep the element instance intact use x-option
elements directly.
The native <option> has a :checked pseudo selector state. This is not possible to polyfill,
so instead <x-option> adds the .\:checked CSS class to any selected option.