webpack.common.js

const path = require("path");
const MiniCssExtractPlugin = require("mini-css-extract-plugin");

module.exports = {
  entry: "./src/index.js",
  output: {
    filename: "js/theme.js",
    path: path.resolve(__dirname, "sphinx_rtd_theme/static")
  },
  module: {
    rules: [
      {
        test: require.resolve("./src/theme.js"),
        use: "imports-loader?this=>window"
      },
      {
        test: /\.sass$/,
        use: [
          {
            loader: MiniCssExtractPlugin.loader
          },
          {
            loader: "css-loader"
          },
          {
            loader: "sass-loader?indentedSyntax",
            options: {
              includePaths: [
                "node_modules/bourbon/app/assets/stylesheets",
                "node_modules/bourbon-neat/app/assets/stylesheets",
                "node_modules/font-awesome/scss",
                "node_modules/wyrm/sass"
              ]
            }
          }
        ]
      },
      {
        test: /\.(woff(2)?|ttf|eot|svg)(\?v=\d+\.\d+\.\d+)?$/,
        use: [
          {
            loader: "file-loader",
            options: {
              name: "[name].[ext]?[hash]",
              outputPath: "fonts/",
              publicPath: "../fonts/"
            }
          }
        ]
      }
    ]
  },
  plugins: [
    new MiniCssExtractPlugin({
      // Options similar to the same options in webpackOptions.output
      // both options are optional
      filename: "css/theme.css"
    })
  ]
};