Generate declaration files for CSS modules

1. Why use this package?
2. How to use this package?
   • Arguments
   • Use Prettier?
   • Can I use the file extension *.module.css?
3. Limitations
4. Compatibility
5. Contributing
6. License

The type definition from @types/css-modules is easy for humans to understand, but not specific enough for programs:

declare module '*.css' {
  const styles: Record<string, string>;

  export default styles;
}

First, you will run into poor developer experience (DX) when noPropertyAccessFromIndexSignature is enabled.

{{! app/components/ui/page.hbs }}
{{! This should work, but results in an error. }}
<div class={{this.styles.container}}>
  {{!-- ↳ Property 'container' comes from an index signature, so it must be accessed with {{get ... 'container'}}. --}}
</div>

{{! A workaround }}
<div class={{get this.styles "container"}}>
</div>

/* app/components/ui/page.gts */
import styles from './page.css';

<template>
  // This should work, but results in an error.
  <div class={{styles.container}}>
    // ↳ Property 'container' comes from an index signature, so it must be accessed with ['container'].
  </div>

  // A workaround
  <div class={{styles['container']}}>
  </div>
</template>

Second, the loose definition may be incompatible with libraries that provide types (e.g. qunit-dom). You will overuse the non-null assertion operator !.

/* tests/integration/components/ui/page-test.ts */
import styles from 'app/components/ui/page.css';

// This should work, but results in an error.
assert
  .dom('[data-test-container]')
  .hasClass(styles.container);
    // ↳ Argument of type 'string | undefined' is not assignable to parameter of type 'string | RegExp'.
    //   Type 'undefined' is not assignable to 'string | RegExp'.

// A workaround
assert
  .dom('[data-test-container]')
  .hasClass(styles['container']!);

When you provide accurate types, libraries (e.g. Glint, embroider-css-modules) improve your DX in return. You can catch typos and type issues early.

{{! app/components/ui/page.hbs }}
<div class={{local this.styles "ontainer"}}> {{! ⚠️ Property 'ontainer' is missing }}
  <h1 class={{this.styles.head}}> {{! ⚠️ Property 'head' does not exist }}
    {{@title}}
  </h1>

  <div class={{local this.style "body"}}> {{! ⚠️ Did you mean 'styles'? }}
    {{yield}}
  </div>
</div>

Install type-css-modules as a development dependency. Ensure that CSS declaration files exist before checking types; for example, you can write a pre-script.

/* package.json */
{
  "scripts": {
    "prelint:types": "type-css-modules <arguments>",
    "lint:types": "tsc --noEmit" // or "glint"
  },
  "devDependencies": {
    "type-css-modules": "...",
    "typescript": "..."
  }
}

You must pass --src to indicate the location(s) of your CSS files.

# One source directory
type-css-modules --src app

# Multiple source directories
type-css-modules --src app/components app/controllers

type-css-modules --root <path/to/your/project>

type-css-modules adds quotation marks in declaration files. This way, the names of CSS class selectors can always be used as object keys.

To separate formatting concerns, configure Prettier to handle *.css.d.ts files differently.

/* .prettierrc.js */
module.exports = {
  overrides: [
    {
      files: '*.css.d.ts',
      options: {
        quoteProps: 'preserve',
      },
    },
  ],
};

Yes! You may use *.module.css to indicate the stylesheets that are for CSS modules. type-css-modules will create declaration files with the extension *.module.css.d.ts.

The Prettier configuration (shown above) can remain as is.

To reduce complexity, type-css-modules expects you to follow the conventions of embroider-css-modules:

• Give the local scope to the styles that you own¹
• Avoid nesting styles²
• Use the default import to import styles

Here are some examples that meet the syntax requirements.

/* app/components/ui/page.css */
.container {
  display: grid;
  grid-template-areas:
    "header"
    "body";
  grid-template-columns: 1fr;
  grid-template-rows: auto 1fr;
  height: calc(100% - 3em);
  overflow-y: auto;
  padding: 1.5rem 1rem;
  scrollbar-gutter: stable;
}

.header {
  grid-area: header;
}

.body {
  grid-area: body;
}

{{! app/components/ui/page.hbs }}
<div class={{local this.styles "container"}}>
  <h1 class={{this.styles.header}}>
    {{@title}}
  </h1>

  <div class="{{this.styles.body}}">
    {{yield}}
  </div>
</div>

/* app/components/ui/page.ts */
import Component from '@glimmer/component';

import styles from './page.css';

export default class UiPageComponent extends Component {
  styles = styles;
}

/* app/components/ui/page.gts */
import { local } from 'embroider-css-modules';

import styles from './page.css';

<template>
  <div class={{local styles "container"}}>
    <h1 class={{styles.header}}>
      {{@title}}
    </h1>

    <div class="{{styles.body}}">
      {{yield}}
    </div>
  </div>
</template>

And some counterexamples (what not to do):

/* app/components/ui/page.css */
:local(.container) {
  display: grid;
  grid-template-areas:
    "header"
    "body";
  grid-template-columns: 1fr;
  grid-template-rows: auto 1fr;
  height: calc(100% - 3em);
  overflow-y: auto;
  padding: 1.5rem 1rem;
  scrollbar-gutter: stable;
}

:local(.header) {
  grid-area: header;
}

:local(.body) {
  grid-area: body;
}

/* app/components/ui/page.css */
.container {
  display: grid;
  grid-template-areas:
    "header"
    "body";
  grid-template-columns: 1fr;
  grid-template-rows: auto 1fr;
  height: calc(100% - 3em);
  overflow-y: auto;
  padding: 1.5rem 1rem;
  scrollbar-gutter: stable;

  .header {
    grid-area: header;
  }

  .body {
    grid-area: body;
  }
}

/* app/components/ui/page.gts */
import { container, header, body } from './page.css';

<template>
  <div class={{container}}>
    <h1 class={{header}}>
      {{@title}}
    </h1>

    <div class="{{body}}">
      {{yield}}
    </div>
  </div>
</template>

^{1. With webpack, for example, you can configure mode to be a function that returns 'local' or 'global'. In stylesheets, you can use the :global() pseudo-class selector to refer to "things from outside."}

^{2. CSS nesting is in spec. To reduce maintenance cost, type-css-modules will leave it up to css-tree to parse nested styles (see issue #210).}

• Node.js v18 or above

See the Contributing guide for details.

This project is licensed under the MIT License.