vite-plugin-standard-css-modules

Provides a CSSStyleSheet or a CSSResult (Lit) for use with import attributes.
Using the "with" keyword and "type : css".

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Allows:

import myStyles1 from './my-styles-1.css' with { type: 'css' };
import myStyles2 from './my-styles-2.css' assert { type: 'css' }; // ⚠️ Deprecated
import myStyles3 from './my-styles-3.css'; // ⚠️ Non-standard

To be imported seamlessly, from your project or a dependency (mono-repo…).

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The API ensures strict defaults while allowing opt-in flexibility, especially for catering to Node usage.

Installation

npm i vite-plugin-standard-css-modules

Vite or compatible frameworks configuration:

import { standardCssModules } from 'vite-plugin-standard-css-modules';

const myEnvironmentViteConfig = {
	// ...

	plugins: [
		standardCssModules({
			/* transformationMode: "CSSResult", */

			filter: (params) => {
				// console.log({ params });

				// if (filePath === "foo") return false;
				// if (params.ssr) return false;

				return true;
			},

			/* log: false, */

			ssrOnlyLit: true, // Removes the need for `?lit`, server-side.
		}),
	],
};

Configuration

targetSsr/targetClient

CSSStyleSheet (default for targetClient) is agnostic, and platform-native.
Might not work with SSR until JS server runtimes support this API or a working minimal implementation.

CSSResult (default for targetSsr) is Lit-specific. On the client, it can lazily provide a CSSStyleSheet.
Works with SSR. Set as default if executed in an SSR environment. That might change in the future, when Node will support CSSStyleSheet.

emptySsr/emptyClient (boolean)

Useful if, for example, you're using Lit hydration and don't want to load the style on client, since they are already provided in the Declarative Shadow Dom as a <style> tag. In that case, you'll set emptyClient to true, resulting in a dummy, empty stylesheet module.

include/exclude (string[])

Absolute glob patterns.
E.g. include: ['**/src/features/counters/counters.scss']

Import flags

?lit

import myStyles1 from './my-styles-1.css?lit' with { type: 'css' };

Overrides CSSStyleSheet to CSSResult on a per-file basis.

For some reasons, like isomorphism, you might want a CSSResult on the client side, but it's not needed otherwise. Lit (on browser) handles those two shapes just fine, without intermediary steps.
It's possible to mix and fit them in the static styles of your custom element.
Also, note that hydration alleviates the need for loading the CSS on the client too, hence the emptyClient option for that cases.

SSR considerations with CSSStyleSheet

If no DOM shims are present in your JS server runtime, you'll get a CSSStyleSheet is not defined.
With a DOM Shim (like the Lit SSR's one), you'll get a replaceSync method is not defined, because the CSSStyleSheet global object is empty.
Solution: use CSSResult here (it is set as the default with SSR).

Environments

• Vite 5
• Vite 5 SSR (ssrModuleLoader)
• Astro 4 Client side JS
• Astro 4 Server side JS

Tested with Node 20 (LTS) and 2024 majors browsers.
Firefox / Safari / Chromium are all supporting constructable stylesheets.

TypeScript

Pre/post processors

Support all Vite's CSS pipelines and formats (PostCSS, Less, SASS…).

IDE awareness

// ./src/vite-env.d.ts
// or
// ./src/env.d.ts

// Add this reference:
/// <reference types="vite-plugin-standard-css-modules/css-modules" />
// (Order matters with Astro)

/// <reference types="vite/client" />
//              (Or `astro/client`)

That way,

import myElementStyles from './my-element.css' with { type: 'css' };
import myElementStyles from './my-element.css?lit' with { type: 'css' };

• ./my-element.css will be cast as CSSStyleSheet
• ./my-element.css?lit will be cast as CSSResult

You can also append them manually in your env.d.ts, see css-modules.d.ts.

Demo

Check out the demo folder.

You'll find an Astro minimal setup, which works exactly the same as with this vite-lit-ssr demo project.

I updated to the latest Lit 3 and Vite 5, and with minor Lit SSR syntax adaption, tested it successfully.

Both of these setups, Homebrewed Lit SSR and Astro, are using ssrLoadModuleLoader.
Basically, you'll get an isomorphic experience thanks to Vite internal tooling which is smoothening environment gaps, minus unresolved DOM limitations in Node.

How it works?

file.css redirects to file.css?raw which by-pass all specific Vite handling.
Then file.css?inline is requested and injected back. This means you should get your usual Vite CSS handling at the end (think all the post-css stuff).

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Since the result is handled like any ?raw imported module with Vite, it's not a "real", living CSS module.
See the rollup-plugin-css-modules documentation for more details about expected limitations, which are shared conceptually, with vite-plugin-standard-css-modules.

Import Attributes

For now, attributes are just "decorative", and act as a reminder for what is a standard CSS Module and what is not.
When Vite will support Import Attributes like Rollup and browsers, those flag will be leveraged and no include/exclude should be needed anymore.

Improvements

• Support for relative globs in include/exclude

Footnotes

100% ESM, dependency-free.

You just need the optional lit peer-dependency, if you're using CSSResult over the default CSSStyleSheet.

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See also rollup-plugin-css-modules.
Its documentation will bring you insights into the state of this API proposal.

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🔗  JulianCataldo.com