webpack.config.js

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

var plugins = [];

var devPlugins = [];

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 === "production" ? prodPlugins : devPlugins
);

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