old_contents: var webpack = require('webpack');
  
  module.exports = {
      entry: [
          'webpack-dev-server/client?http://localhost:8080',
          'webpack/hot/only-dev-server',
          './src/index.jsx'
      ],
      module: {
          loaders: [{
              test: /\.jsx?$/,
              exclude: /node_modules/,
              loader: 'react-hot!babel'
          }]
      },
      resolve: {
          extensions: ['', '.js', '.jsx']
      },
      output: {
          path: __dirname + '/dist',
          publicPath: '/',
          filename: 'bundle.js'
      },
      devServer: {
          contentBase: './dist',
          hot: true
      },
      plugins: [
          new webpack.HotModuleReplacementPlugin()
      ]
  };
new_contents: var webpack = require('webpack');
  
  module.exports = {
      entry: [
          'webpack-dev-server/client?http://localhost:8080',
          'webpack/hot/only-dev-server',
          './src/index.jsx'
      ],
      module: {
          loaders: [{
              test: /\.jsx?$/,
              exclude: /node_modules/,
              loader: 'react-hot!babel'
          }]
      },
      resolve: {
          extensions: ['', '.js', '.jsx']
      },
      output: {
          path: __dirname + '/dist',
          publicPath: '/',
          filename: 'bundle.js'
      },
      devServer: {
          contentBase: './dist',
          hot: true
      },
      devtool: 'source-map',
      plugins: [
          new webpack.HotModuleReplacementPlugin()
      ]
  };
subject: Create source maps