old_contents: const merge = require('webpack-merge');
  const path = require('path');
  const webpack = require('webpack');
  
  const TARGET = process.env.npm_lifecycle_event;
  const PATHS = {
    app: path.join(__dirname, 'app'),
    build: path.join(__dirname, 'build')
  };
  
  const common = {
    // Entry accepts a path or an object of entries. We'll be using the
    // latter form given it's convenient with more complex configurations.
    entry: {
      app: PATHS.app
    },
    output: {
      path: PATHS.build,
      filename: 'bundle.js'
    },
    module: {
      loaders: [
        {
          // Test expects a RegExp! Note the slashes!
          test: /\.css$/,
          loaders: ['style', 'css'],
          // Include accepts either a path or an array of paths.
          include: PATHS.app
        }
      ]
    }
  };
  
  if (TARGET === 'start' || !TARGET) {
    module.exports = merge(common, {
      devServer: {
        contentBase: PATHS.build,
          // Enable history API fallback so HTML5 History API based
          // routing works. This is a good default that will come
          // in handy in more complicated setups.
          historyApiFallback: true,
          hot: true,
          inline: true,
          progress: true,
  
          // Display only errors to reduce the amount of output.
          stats: 'errors-only',
  
          // Parse host and port from env so this is easy to customize.
          //
          // If you use Vagrant or Cloud9, set
          // host: process.env.HOST || '0.0.0.0';
          //
          // 0.0.0.0 is available to all network devices unlike default
          // localhost
          host: process.env.HOST,
          port: process.env.PORT
        },
        plugins: [
          new webpack.HotModuleReplacementPlugin()
        ]
    });
  }
  
  if(TARGET === 'build') {
    module.exports = merge(common, {});
  }
  
new_contents: const merge = require('webpack-merge');
  const path = require('path');
  const webpack = require('webpack');
  
  const TARGET = process.env.npm_lifecycle_event;
  const PATHS = {
    app: path.join(__dirname, 'app'),
    build: path.join(__dirname, 'build')
  };
  
  const common = {
    // Entry accepts a path or an object of entries. We'll be using the
    // latter form given it's convenient with more complex configurations.
    entry: {
      app: PATHS.app
    },
    output: {
      path: PATHS.build,
      filename: 'bundle.js'
    },
    module: {
      loaders: [
        {
          // Test expects a RegExp! Note the slashes!
          test: /\.css$/,
          loaders: ['style', 'css'],
          // Include accepts either a path or an array of paths.
          include: PATHS.app
        }
      ]
    }
  };
  
  if (TARGET === 'start' || !TARGET) {
    module.exports = merge(common, {
      devtool: 'eval-source-map',
      devServer: {
        contentBase: PATHS.build,
          // Enable history API fallback so HTML5 History API based
          // routing works. This is a good default that will come
          // in handy in more complicated setups.
          historyApiFallback: true,
          hot: true,
          inline: true,
          progress: true,
  
          // Display only errors to reduce the amount of output.
          stats: 'errors-only',
  
          // Parse host and port from env so this is easy to customize.
          //
          // If you use Vagrant or Cloud9, set
          // host: process.env.HOST || '0.0.0.0';
          //
          // 0.0.0.0 is available to all network devices unlike default
          // localhost
          host: process.env.HOST,
          port: process.env.PORT
        },
        plugins: [
          new webpack.HotModuleReplacementPlugin()
        ]
    });
  }
  
  if(TARGET === 'build') {
    module.exports = merge(common, {});
  }
  
subject: Add source maps