adamsanderson / container-query-polyfill

A polyfill for CSS Container Queries

Container Query Polyfill

A tiny polyfill for CSS Container Queries, weighing about 1.6kB brotli’d. It transpiles CSS code on the client-side and implements Container Query functionality using ResizeObserver and MutationObserver.

Usage

Ideally, the polyfill is only loaded if the browser doesn’t support Container Queries natively. In a modern setup with a bundler that uses ES modules, the following snippet should work:

const supportsContainerQueries = "container" in document.documentElement.style;
if (!supportsContainerQueries) {
  import("container-query-polyfill");
}

If you are in a legacy setup (or just want to prototype quickly), there’s also an IIFE version that you can include using a <script> tag:

<script src="https://unpkg.com/container-query-polyfill/cqfill.iife.min.js"></script>

Browser support

The polyfull should work in all modern browsers. Chrome 88+, Firefox 78+ and Safari 14+.

Limitations

To keep the polyfill performant, small and maintainable, I have make certain tradeoffs with full feature parity of the Container Query spec. I have listed these tradeoffs below.

(These decisions can be revisited if they pose a significant hurdle and there is a good way to implement them. Please open an issue!)

• Container Queries will not work when nested inside a Media Query. For now, the polyfill only supports top-level CQs.
• Container query thresholds can only be specified using pixels.
• Due to the nature of CORS, the polyfill only attempts to handle same-origin and inline stylesheets. Cross-origin stylesheets are ignored, regardless of CORS headers.
• Don’t do weird interspersed comments, okay? Like @container /* here’s a comment! */ (min-width: 1px) { ... }. Just don’t.

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License Apache-2.0