How to configure webpack to generate multiple CSS theme files?

Question

I have multiple theme files, which are basically SASS files with different variables that specify colors, fonts etc. specific to each theme. The rest of the SASS files in the project use these variables in their CSS rules.

I would like to configure webpack in such a way that it will generate 1 CSS file for each theme file.

For example:

main.scss:

body {
  background-color: $theme-specific-color;
}

theme1.scss:

$theme-specific-color: blue;

theme2.scss:

$theme-specific-color: green;

The desired configuration would output 2 CSS files:

theme1.css:

body {
  background-color: blue;
}

theme2.css:

body {
  background-color: green;
}

I'm currently using ExtractTextPlugin to extract the stylesheets into CSS.

Answer 1

I finally found a solution. What I did is generate the css with a variable ($theme)having different values for each generated css file. And in my code, my style depends on the value of $theme.

It is working with (yes, these are old version. Sorry):

"webpack": "2.2.0",
"webpack-combine-loaders": "2.0.3",
"multi-loader": "git://github.com/sshmyg/multi-loader.git#cbaa35f8936a939968adb78301be0204e36f30cd",
"extract-text-webpack-plugin": "git://github.com/ONE-LOGIC/extract-text-webpack-plugin.git#831af7b65ce749069993e60bd9cb51c637d4e98b",

then my webpack config contains this:

const extractDark = new ExtractTextPlugin({ filename: `css/style.dark.css`, allChunks: true });
const extractLight = new ExtractTextPlugin({ filename: `css/style.light.css`, allChunks: true });
...
config.module: {
  rules: [
    {
    test: /\.css$/,
    use: extractDark.extract({
      fallback: 'style-loader',
      use: [
        { loader: 'css-loader', query: { sourceMap: true } },
        { loader: 'postcss-loader' },
      ],
    }),
  }, {
    test: /\.css$/,

    use: extractLight.extract({
      fallbackLoader: 'style-loader',
      use: [
        { loader: 'css-loader', query: { sourceMap: true } },
        { loader: 'postcss-loader' },
      ],
    }),
  },
  {
    test: /\.scss$/,
    use: multi(
      combineLoaders(extractDark.extract({
        fallback: 'style-loader',
        use: [
          {
            loader: 'css-loader',
          }, {
            loader: 'resolve-url-loader',
          }, {
            loader: 'sass-loader',
            options: {
              includePaths: [],
              sourceMap: true,
              data: '$theme: dark;',
            },
          },
        ],
      })),
      combineLoaders(extractLight.extract({
        fallback: 'style-loader',
        use: [
          {
            loader: 'css-loader',
          }, {
            loader: 'resolve-url-loader',
          }, {
            loader: 'sass-loader',
            options: {
              includePaths: [],
              sourceMap: true,
              data: '$theme: light;',
            },
          },
        ],
      }))
    ),
  }
  ]
};
....
config.plugins.push(extractDark, extractLight);

Finally, my stylesheets have code like this:

$backgroundcolor: white;

@if $theme == dark {
  $backgroundcolor: black;
}

.myClass {
  background-color: $backgroundcolor;
}