Extends

extends

string | string[]

The extends property allows you to extend an existing configuration to use as the base. It internally uses the webpack-merge package to merge the configurations and helps you to avoid duplicating configurations between multiple configurations.

base.webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        use: 'babel-loader',
        exclude: /node_modules/,
      },
      {
        test: /\.css$/,
        use: ['style-loader', 'css-loader'],
      },
    ],
  },
  plugins: [
    new webpack.DefinePlugin({
      'process.env.NODE_ENV': JSON.stringify('production'),
    }),
  ],
};

webpack.config.js

module.exports = {
  extends: path.resolve(__dirname, './base.webpack.config.js'),
  entry: './src/index.js',
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'bundle.js',
  },
};

Extending multiple configurations

You can extend multiple configurations at once by passing an array of configuration paths to the extends property.

Configurations from the extends property are merged from right to left, meaning that the configuration on the right will be merged into the configuration on the left. Configuration can be overridden by passing the same property in the configuration on the right.

js.webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        use: 'babel-loader',
        exclude: /node_modules/,
      },
    ],
  },
};

css.webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: ['style-loader', 'css-loader'],
      },
    ],
  },
};

webpack.config.js

module.exports = {
  extends: [
    path.resolve(__dirname, './js.webpack.config.js'),
    path.resolve(__dirname, './css.webpack.config.js'),
  ],
  entry: './src/index.js',
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'bundle.js',
  },
};

Overridding Configurations

You can override configurations from the extended configuration by passing the same property in the configuration that extends it.

base.webpack.config.js

module.exports = {
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'bundle.js',
  },
};

webpack.config.js

module.exports = {
  extends: path.resolve(__dirname, './base.webpack.config.js'),
  entry: './src/index.js',
  // overriding the output path and filename
  output: {
    path: path.resolve(__dirname, 'build'),
    filename: '[name].bundle.js',
  },
};

Loading configuration from external packages

You can also load configuration from third-party packages by passing the package name to the extends property. The package must export the webpack configuration in package.json.

webpack.config.js

module.exports = {
  extends: require.resolve('webpack-config-foo'),
  entry: './src/index.js',
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'bundle.js',
  },
};