jackfranklin / 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

My aim is to make the polyfill work correctly for the majority of use-cases, but cut corners where possible to keep the polyfill simple(-ish), small and efficient. The limitations arising from these tradeoffs are listed 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!)

• Only a subset of queries are supported for now. Specifically, only min-width, max-width, min-height and max-height are supported. Additionally, the polyfill does support and, or or not.
• 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.

Building & Testing

This project uses esbuild to bundle the project, which is automatically installed via npm. To build the polyfill, run:

npm run build

To run the tests, run

npm run serve

and open your browser at http://127.0.0.1:3474/tests.

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License Apache-2.0