To import bootstrap .js and .css files with Webpack, we add it the paths to resolve the files into the Webpack config.

To do this, we write

module.exports = {
  resolve: {
    alias: {
      jquery: path.join(
        __dirname,
        "development/bower_components/jquery/jquery"
      ),
    },
    root: srcPath,
    extensions: ["", ".js", ".css"],
    modulesDirectories: [
      "node_modules",
      srcPath,
      commonStylePath,
      bootstrapPath,
    ],
  },
};

to make Webpack resolve the directories in the modulesDirectories array.

And we include the extensions of the files to resolve in the extensions array.