code: function getExternals() {
  	const externals = {};
  
  	// Don't bundle any node_modules, both to avoid a massive bundle, and problems
  	// with modules that are incompatible with webpack bundling.
  	fs.readdirSync( 'node_modules' )
  		.filter( function( module ) {
  			return [ '.bin' ].indexOf( module ) === -1;
  		} )
  		.forEach( function( module ) {
  			externals[ module ] = 'commonjs ' + module;
  		} );
  
  	// Don't bundle webpack.config, as it depends on absolute paths (__dirname)
  	externals[ 'webpack.config' ] = 'commonjs webpack.config';
  	// Exclude hot-reloader, as webpack will try and resolve this in production builds,
  	// and error.
  	externals[ 'bundler/hot-reloader' ] = 'commonjs bundler/hot-reloader';
  	// Exclude the devdocs search-index, as it's huge.
  	externals[ 'devdocs/search-index' ] = 'commonjs devdocs/search-index';
  	// Exclude the devdocs components usage stats data
  	externals[ 'devdocs/components-usage-stats.json' ] =
  		'commonjs devdocs/components-usage-stats.json';
  	// Exclude server/bundler/assets, since the files it requires don't exist until the bundler has run
  	externals[ 'bundler/assets' ] = 'commonjs bundler/assets';
  	// Map React and redux to the minimized version in production
  	if ( config( 'env' ) === 'production' ) {
  		externals.react = 'commonjs react/umd/react.production.min.js';
  		externals.redux = 'commonjs redux/dist/redux.min';
  	}
  
  	return externals;
  }
docs: This lists modules that must use commonJS `require()`s
  All modules listed here need to be ES5.
  
  @returns { object } list of externals