webpack.config.js

const path = require('path');
const webpack = require('webpack');

let plugins = [];
const devPlugins = [];

const prodPlugins = [
  new webpack.DefinePlugin({
    'process.env': {
      NODE_ENV: JSON.stringify('production'),
    },
  }),
  new webpack.optimize.UglifyJsPlugin({
    compress: {
      warnings: true,
    },
  }),
];

plugins = plugins.concat(process.env.NODE_ENV === 'production' ? prodPlugins : devPlugins);

module.exports = {
  entry: './frontend/index.js',
  output: {
    path: path.resolve(__dirname, 'app', 'assets', 'javascripts'),
    filename: 'bundle.js',
  },
  plugins,
  module: {
    loaders: [
      {
        test: [/\.jsx?$/],
        exclude: /(node_modules)/,
        loader: 'babel-loader',
        query: {
          presets: ['env', 'react'],
        },
      },
    ],
  },
  devtool: 'source-map',
  resolve: {
    extensions: ['.js', '.jsx', '*'],
  },
};