Asynchronous Webpack Configuration

webpack.config.prod.js

...

// Build your configuration object, and then return a Promise

let finalConfig = {
  devtool: 'eval',
  output: { /* your configuration */ },
  plugins: [ /* your configuration */ ]
};

module.exports = new Promise(resolve => {
  getGitAndPackageInformation((gitAndPackageConfiguration) => {
    // Add something to 
    finalConfig.plugins.unshift(new webpack.DefinePlugin({
      __BUILD__: JSON.stringify(gitAndPackageConfiguration)
    }));

    resolve(finalConfig);
  })
});