oddbirdPopover Attribute Polyfill
This polyfills the HTML popover attribute and
showPopover/hidePopover/togglePopover methods onto HTMLElement, as well as
the popovertarget and popovertargetaction attributes on Button elements.
Polyfill Installation
Download a copy
The simplest, recommended way to install the polyfill is to copy it into your project.
Download popover.js (or popover.min.js) from
unpkg.com and add it
to the appropriate directory in your project. Then, include it where necessary
with a <script> tag:
<script src="/path/to/popover.min.js" type="module"></script>
Or without JavaScript modules:
<script src="/path/to/popover.iife.min.js"></script>
Note that the JS will inject CSS styles into your document (or ShadowRoot).
With npm
For more advanced configuration, you can install with npm:
npm install @oddbird/popover-polyfill
After installing, you’ll need to use appropriate tooling to use
node_modules/@oddbird/popover-polyfill/dist/popover.js.
For most tooling such as Vite, Webpack, and Parcel, that will look like this:
import '@oddbird/popover-polyfill';
If you want to manually apply the polyfill, you can instead import the
isSupported and apply functions directly from
node_modules/@oddbird/popover-polyfill/dist/popover-fn.js file.
With most tooling:
import { apply, isSupported } from '@oddbird/popover-polyfill/fn';
Or in CommonJS environments:
const { apply, isSupported } = require('@oddbird/popover-polyfill/fn');
An isPolyfilled function is also available, to detect if the Popover methods
have been polyfilled:
import { isPolyfilled } from '@oddbird/popover-polyfill/fn';
Via CDN
For prototyping or testing, you can use the npm package via a Content Delivery Network. Avoid using JavaScript CDNs in production, for many good reasons such as performance and robustness.
<script
src="https://cdn.jsdelivr.net/npm/@oddbird/popover-polyfill@latest"
crossorigin="anonymous"
defer
></script>
Usage
After installation the polyfill will automatically add the correct methods and attributes to the HTMLElement class.
Caveats
This polyfill is not a perfect replacement for the native behavior; there are some caveats which will need accommodations:
A native
popoverhas a:popover-openpseudo selector when in the open state. Pseudo selectors cannot be polyfilled within CSS, and so instead the polyfill will add the.\:popover-openCSS class to any open popover. In other words a popover in the open state will haveclass=":popover-open". In CSS the:character must be escaped with a backslash.The
:popover-openselector within JavaScript methods has been polyfilled, so both.querySelector(':popover-open')and.querySelector('.\:popover-open')will work to select the same element.matchesandclosesthave also been patched, so.matches(':popover-open')will work the same as.matches('.\:popover-open').Using native
:popover-openin CSS that does not support nativepopoverresults in an invalid selector, and so the entire declaration is thrown away. This is important because if you intend to style a popover using.\:popover-openit will need to be a separate declaration. For example,[popover]:popover-open, [popover].\:popover-openwill not work.
Native
popoverelements use the:top-layerpseudo element which gets placed above all other elements on the page, regardless of overflow or z-index. This is not possible to polyfill, and so this library simply sets a really highz-index. This means if a popover is within an element that hasoverflow:orposition:CSS, then there will be visual differences between the polyfill and the native behavior.Native invokers (that is, buttons or inputs using the
popovertargetattribute) onpopover=autowill render in the accessibility tree as elements withexpanded. The only way to do this in the polyfill is setting thearia-expandedattribute on those elements. This may impact mutation observers or frameworks which do DOM diffing, or it may interfere with other code which setsaria-expandedon elements.The polyfill uses
adoptedStyleSheetsandnew CSSStyleSheet()to inject CSS onto the page (and each Shadow DOM). If it can't use that it'll generate a<style>tag instead. This means you may see a<style>tag you didn't put there, and this may impact mutation observers or frameworks.For browsers which don't support
new CSSStyleSheet(), if you are building a ShadowRoot by setting.innerHTML, you'll remove the StyleSheet. CallinjectStyles(myShadow)to add the styles back in:let supportsCSSStyleSheet = false; try { new CSSStyleSheet(); supportsCSSStyleSheet = true; } catch {} const myShadow = myHost.attachShadow({ mode: 'open' }); myShadow.innerHTML = `...`; if (!supportsCSSStyleSheet) { injectStyles(myShadow); }Similarly, if you're using Declarative ShadowDOM or otherwise creating a shadow root without calling
attachShadow/attachInternals, then the polyfill won't inject the styles (because it can't reference theshadowRoot). You'll need to manually inject the styles yourself withinjectStyles(myShadow).As a stylesheet is injected into the main document, if your host element is a popover, styling with
:hostgets tricky beause:hoststyles always take lower precedence than the main document styles. This is a limitation of CSS and there's not a reasonable workaround. The best workaround for now is to add!importantto conflicting properties in your:hostrule. See #147 for more.Given that the CSS is injected using JavaScript, you may find that you temporarily see popovers as open while the JS is loading. To work around this, you can add the following CSS to your project:
@supports not selector(:popover-open) { [popover]:not(.\:popover-open) { display: none; } }
When supported, the polyfill creates a cascade layer named
popover-polyfill. If your styles are not in layers then this should have no impact. If your styles do use layers, you'll need to ensure the polyfill layer is declared first. (e.g.@layer popover-polyfill, other, layers;)While
togglePopover()supports both theforce: booleanand{force: boolean, source: HTMLElement}syntax, bothshowPopover()andtogglePopover()disregard thesourceparameter.The polyfill will not work in browsers with partial popover support enabled, and will also not attempt to make experimental support match the final spec.
Contributing
Visit our contribution guidelines.
Sponsor OddBird's OSS Work
At OddBird, we love contributing to the languages & tools developers rely on. We're currently working on polyfills for new Popover & Anchor Positioning functionality, as well as CSS specifications for functions, mixins, and responsive typography. Help us keep this work sustainable and centered on your needs as a developer! We display sponsor logos and avatars on our website.