Popover Attribute Polyfill

• Demo
• Explainer

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>

You will also likely need the CSS file, which supplies some default styles. Download popover.css from unpkg.com and add it to the appropriate directory in your project. Then, include it where necessary with a <link rel=stylesheet> tag:

<link rel="stylesheet" src="/path/to/popover.css" />

Note that default styles will not be applied to shadow roots. Each root node will need to include the styles separately.

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.

You will also likely need to include the CSS stylesheet which is found in node_modules/@oddbird/popover-polyfill/dist/popover.css.

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.

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.

<link
  rel="stylesheet"
  href="https://cdn.jsdelivr.net/npm/@oddbird/popover-polyfill@latest/dist/popover.css"
  crossorigin="anonymous"
/>
<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:

• Native popover has an :open and :closed pseudo selector state. This is not possible to polyfill, so instead this adds the .\:open CSS class to any open popover.

  • :closed is not implemented due to difficulty in finding popover elements during page load. As such, you'll need to style them using :not(.\:open).

  • Using native :open in CSS that does not support native popover results in an invalid selector, and so the entire declaration is thrown away. This is important because if you intend to style a popover using .\:open it will need to be a separate declaration. For example, [popover]:open, [popover].\:open will not work.

• Native popover elements use the :top-layer pseudo 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 high z-index. This means if a popover is within an element that has overflow: or position: CSS, then there will be visual differences between the polyfill and the native behavior.

• Native invokers (that is, buttons or inputs using the popovertarget attribute) on popover=auto will render in the accessibility tree as elements with expanded. The only way to do this in the polyfill is setting the aria-expanded attribute on those elements. This may impact mutation observers or frameworks which do DOM diffing, or it may interfere with other code which sets aria-expanded on elements.

Contributing

Visit our contribution guidelines.