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oddbird / css-anchor-positioning

Polyfill for CSS Anchor Positioning
https://anchor-positioning.oddbird.net/
BSD 3-Clause "New" or "Revised" License
265 stars 10 forks source link
css polyfill

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CSS Anchor Positioning Polyfill

Build Status

Netlify Status

Browser Support

Getting Started

To use the polyfill, add this script tag to your document <head>:

<script type="module">
  if (!("anchorName" in document.documentElement.style)) {
    import("https://unpkg.com/@oddbird/css-anchor-positioning");
  }
</script>

If you want to manually apply the polyfill, you can instead import the polyfill function directly from the @oddbird/css-anchor-positioning/dist/css-anchor-positioning-fn.js file.

For build tools such as Vite, Webpack, and Parcel, that will look like this:

import polyfill from '@oddbird/css-anchor-positioning/fn';

The polyfill function returns a promise that resolves when the polyfill has been applied.

You can view a more complete demo here.

Configuration

The polyfill supports a small number of options. When using the default version of the polyfill that executes automatically, options can be set by setting the value of window.ANCHOR_POSITIONING_POLYFILL_OPTIONS.

<script type="module">
  if (!("anchorName" in document.documentElement.style)) {
    window.ANCHOR_POSITIONING_POLYFILL_OPTIONS = {
      elements: undefined,
      excludeInlineStyles: false,
      useAnimationFrame: false,
    };
    import("https://unpkg.com/@oddbird/css-anchor-positioning");
  }
</script>

When manually applying the polyfill, options can be set by passing an object as an argument.

<script type="module">
  if (!("anchorName" in document.documentElement.style)) {
    const { default: polyfill } = await import("https://unpkg.com/@oddbird/css-anchor-positioning/dist/css-anchor-positioning-fn.js");

    polyfill({
      elements: undefined,
      excludeInlineStyles: false,
      useAnimationFrame: false,
    });
  }
</script>

elements

type: HTMLElements[], default: undefined

If set, the polyfill will only be applied to the specified elements instead of to all styles. Any specified <link> and <style> elements will be polyfilled. By default, all inline styles in the document will also be polyfilled, but if excludeInlineStyles is true, only inline styles on specified elements will be polyfilled.

excludeInlineStyles

type: boolean, default: false

When not defined or set to false, the polyfill will be applied to all elements that have eligible inline styles, regardless of whether the elements option is defined. When set to true, elements with eligible inline styles listed in the elements option will still be polyfilled, but no other elements in the document will be implicitly polyfilled.

useAnimationFrame

type: boolean, default: false

Determines whether anchor calculations should update on every animation frame (e.g. when the anchor element is animated using transforms), in addition to always updating on scroll/resize. While this option is optimized for performance, it should be used sparingly.

For legacy support, this option can also be set by setting the value of window.UPDATE_ANCHOR_ON_ANIMATION_FRAME, or, when applying the polyfill manually, by passing a single boolean with polyfill(true).

Limitations

This polyfill was implemented against an early version of the spec, and updates were paused to allow the syntax to solidify. Now that browsers are working on implementation, we are in the process of bringing it up to date.

While this polyfill supports many basic use cases, it doesn't (yet) support the following features:

In addition, JS APIs like CSSPositionTryRule or CSS.supports will not be polyfilled.

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.

Sponsor OddBird's OSS Work