@oddbird/css-anchor-positioning
v0.3.1
Published
Polyfill for the proposed CSS anchor positioning spec
Downloads
5,756
Readme
CSS Anchor Positioning Polyfill
Browser Support
- Firefox 54+
- Chrome 51+
- Edge 79+
- Safari 10+
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 transform
s), 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:
- The following portions of Position Fallback:
position-try-order
. Iftry-size
is specified inposition-try
shorthand, it will be parsed, andtry-tactics
will be applied, but thetry-size
will be ignored.- The
flip-start
try-tactic
is only partially supported. The tactic is only applied to property names and anchor sides. - a
position-area
as atry-tactic
- Fallback does not support percentage anchor-side values, nor anchor functions that are passed through custom properties.
- Polyfill allows anchoring in scroll more permissively than the spec allows,
for instance without a default
position-anchor
. anchor-scope
property on pseudo-elementsposition-area
propertyanchor-center
value forjustify-self
,align-self
,justify-items
, andalign-items
properties- anchor functions with
implicit
anchor-element - automatic anchor positioning: anchor functions with
inside
oroutside
anchor-side position-visibility
property- dynamically added/removed anchors or targets
- anchors or targets in the shadow-dom
- anchor functions assigned to
inset-*
properties orinset
shorthand property - vertical/rtl writing-modes (partial support)
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.