webpack.config.js

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

var plugins = []; // if using any plugins for both dev and production
var devPlugins = []; // if using any plugins for development

var 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 === 'development' ? devPlugins : prodPlugins
);

module.exports = {
  context: __dirname,
  entry: './frontend/app.jsx',
  output: {
    path: path.resolve(__dirname, 'app', 'assets', 'javascripts'),
    filename: './bundle.js'
  },
  resolve: {
    extensions: ['.js', '.jsx', '*']
  },
  plugins: plugins,
  module: {
    loaders: [
      {
        test: /\.jsx?$/,
        exclude: /(node_modules)/,
        loader: 'babel-loader',
        query: {
          presets: ['react', 'es2015']
        }
      }
    ]
  },
  devtool: 'source-maps',
};