typings-for-css-modules-loader

Webpack loader that works as a css-loader drop-in replacement to generate TypeScript typings for CSS modules on the fly

Installation

Install via npm npm install --save-dev typings-for-css-modules-loader

Options

Just like any other loader you can specify options e.g. as query-params

css-loader options

Any option that your installed version of css-loader supports can be used and will be passed to it.

namedExport-option

As your fellow css-developer may tend to use characters like dashes(-) that are not valid characters for a typescript variable the default behaviour for this loader is to export an interface as the default export that contains the classnames as properties. e.g.:

export interface IExampleCss {
  'foo': string;
  'bar-baz': string;
}
declare const styles: IExampleCss;

export default styles;

A cleaner way is to expose all classes as named exports, this can be done if you enable the namedExport-option. e.g.

  { test: /\.css$/, loader: 'typings-for-css-modules-loader?modules&namedExport' }

As mentioned above, this requires classnames to only contain valid typescript characters, thus filtering out all classnames that do not match /^\w+$/i. (feel free to improve that regexp) In order to make sure that even classnames with non-legal characters are used it is highly recommended to use the camelCase-option as well, that - once passed to the css-loader - makes sure all classnames are transformed to valid variables. with:

  { test: /\.css$/, loader: 'typings-for-css-modules-loader?modules&namedExport&camelCase' }

using the following css:

.foo {
  color: white;
}

.bar-baz {
  color: green;
}

will generate the following typings file:

export const foo: string;
export const barBaz: string;

css-loader exports mappings to exports.locals which is incompatible with the namedExport-option unless paired with extract-text-webpack-plugin or style-loader. They move the exported properties from exports.locals to exports making them required for namedExport to work, and namedExport required for them to work. Always combine usage of extract-text-webpack-plugin or style-loader with the namedExport-option.

silent-option

To silence the loader because you get annoyed by its warnings or for other reasons, you can simply pass the "silent" query to the loader and it will shut up. e.g.:

  { test: /\.css$/, loader: 'typings-for-css-modules-loader?silent' }

banner-option

To add a "banner" prefix to each generated *.d.ts file, you can pass a string to this option as shown below. The prefix is quite literally prefixed into the generated file, so please ensure it conforms to the type definition syntax.

  { test: /\.css$/, loader: 'typings-for-css-modules?banner="// This file is automatically generated by typings-for-css-modules.\n// Please do not change this file!"' }

Usage

Keep your webpack.config as is just instead of using css-loader use typings-for-css-modules-loader its important you keep all the params that you used for the css-loader before, as they will be passed along in the process

before:

webpackConfig.module.loaders: [
    { test: /\.css$/, loader: 'css?modules' }
    { test: /\.scss$/, loader: 'css?modules&sass' }
];

after:

webpackConfig.module.loaders: [
    { test: /\.css$/, loader: 'typings-for-css-modules-loader?modules' }
    { test: /\.scss$/, loader: 'typings-for-css-modules-loader?modules&sass' }
];

Example

Imagine you have a file ~/my-project/src/component/MyComponent/myComponent.scss in your project with the following content:

.some-class {
  // some styles
  &.someOtherClass {
    // some other styles
  }
  &-sayWhat {
    // more styles
  }
}

Adding the typings-for-css-modules-loader will generate a file ~/my-project/src/component/MyComponent/myComponent.scss.d.ts that has the following content:

export interface IMyComponentScss {
  'some-class': string;
  'someOtherClass': string;
  'some-class-sayWhat': string;
}
declare const styles: IMyComponentScss;

export default styles;

using namedExport with the camelCase-option

Using the namedExport as well as the camelCase options the generated file will look as follow:

export const someClass: string;
export const someOtherClass: string;
export const someClassSayWhat: string;

Example in Visual Studio Code

If you encounter the following errors:

error TS1192: Module '"xxxxx/xxxx/src/style.sass"' has no default export.

maybe you should export the styles as following:

import * as styles from './style.sass';

Support

As the loader just acts as an intermediary it can handle all kind of css preprocessors (sass, scss, stylus, less, ...). The only requirement is that those preprocessors have proper webpack loaders defined - meaning they can already be loaded by webpack anyways.

Requirements

The loader uses css-loader(https://github.com/webpack/css-loader) under the hood. Thus it is a peer-dependency and the expected loader to create CSS Modules.

Known issues

Webpack rebuilds / builds slow

As the loader generates typing files, it is wise to tell webpack to ignore them. The fix is luckily very simple. Webpack ships with a "WatchIgnorePlugin" out of the box. Simply add this to your webpack plugins:

plugins: [
    new webpack.WatchIgnorePlugin([
      /css\.d\.ts$/
    ]),
    ...
  ]

where css is the file extension of your style files. If you use sass you need to put sass here instead. If you use less, stylus or any other style language use their file ending.

Typescript doesnt find the typings

As the webpack process is independent from your typescript "runtime" it may take a while for typescript to pick up the typings. Any hints on how this could be fixed deterministically are welcome!