Besides exporting a single config object, there are a few more ways that cover other needs as well.

Exporting a Function

Eventually you will find the need to disambiguate in your webpack.config.js between development and production builds. You have (at least) two options:

One option is to export a function from your webpack config instead of exporting an object. The function will be invoked with two arguments:

• An environment as the first parameter. See the environment options CLI documentation for syntax examples.
• An options map (argv) as the second parameter. This describes the options passed to webpack, with keys such as output-filename and optimize-minimize.

-module.exports = {
+module.exports = function(env, argv) {
+  return {
+    mode: env.production ? 'production' : 'development',
+    devtool: env.production ? 'source-maps' : 'eval',
     plugins: [
       new TerserPlugin({
         terserOptions: {
+          compress: argv['optimize-minimize'] // only if -p or --optimize-minimize were passed
         }
       })
     ]
+  };
};

Exporting a Promise

webpack will run the function exported by the configuration file and wait for a Promise to be returned. Handy when you need to asynchronously load configuration variables.

It is possible to export multiple promises by wrapping them into Promise.all([/* Your promises */]).

module.exports = () => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve({
        entry: './app.js',
        /* ... */
      });
    }, 5000);
  });
};

Returning a Promise only works when using webpack via CLI. webpack() expects an object.

Exporting multiple configurations

Instead of exporting a single configuration object/function, you may export multiple configurations (multiple functions are supported since webpack 3.1.0). When running webpack, all configurations are built. For instance, this is useful for bundling a library for multiple targets such as AMD and CommonJS:

module.exports = [{
  output: {
    filename: './dist-amd.js',
    libraryTarget: 'amd'
  },
  name: 'amd',
  entry: './app.js',
  mode: 'production',
}, {
  output: {
    filename: './dist-commonjs.js',
    libraryTarget: 'commonjs'
  },
  name: 'commonjs',
  entry: './app.js',
  mode: 'production',
}];

If you pass a name to --config-name flag, webpack will only build that specific configuration.