webpack dev server does not show the content
<p>I have the following problem when running the webpack dev server: 
when I run npm start, it show the following: </p>

<blockquote>
  <p>➜  directory git:(staging) ✗ npm start </p>
  
  <p>directory @1.0.0 start directory
  BUILD_DEV=1 BUILD_STAGING=1 ./node_modules/webpack-dev-server/bin/webpack-dev-server.js</p>
  
  <p><a href="http://localhost:8080/" rel="nofollow noreferrer">http://localhost:8080/</a></p>
  
  <p><strong>webpack result is served from /undefined/</strong></p>
  
  <p>content is served from </p>
  
  <p>directory 
  404s will fallback to /index.html</p>
  
  <p>Hash: 75773622412153d5f921</p>
  
  <p>Version: webpack 1.12.11</p>
  
  <p>Time: 43330ms</p>
</blockquote>

<p>I guess the problem might because the following line: 
<strong>webpack result is served from /undefined/</strong></p>

<p>When I open the browser at <strong><a href="http://localhost:8080/" rel="nofollow noreferrer">http://localhost:8080/</a></strong>, it appear as follow: </p>

<blockquote>
  <p>Cannot GET /</p>
</blockquote>

<p>and there is no thing in the console. </p>

<p>Do you have any ideas for this problem ? </p>

<p><strong>UPDATE: WEBPACK CONFIG FILE</strong></p>

<pre><code>const webpack = require('webpack');
const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const merge = require('webpack-merge');
const nodeModulesDir = path.resolve(__dirname, 'node_modules');

const deps = [
  'moment/min/moment.min.js',
  'underscore/underscore-min.js',
];

/* Include SASS path here if you want to this in your sass files:
 *   @import 'bourbon';
 */
const bourbon = require('node-bourbon').includePaths;

const TARGET = process.env.npm_lifecycle_event;
const ROOT_PATH = path.resolve(__dirname);
const SASS_DEPS = [bourbon].toString();

const BUILD_NUMBER = process.env.CI_BUILD_NUMBER;

const common = {
  entry: path.resolve(ROOT_PATH, 'app/index.js'),
  output: {
    filename: BUILD_NUMBER + '-[hash].js',
    path: path.resolve(ROOT_PATH, 'build'),
    publicPath: `/${BUILD_NUMBER}/`,
  },
  module: {
    loaders: [
      {
        test: /\.scss$/,
        loaders: ['style', 'css', 'sass?includePaths[]=' + SASS_DEPS],
        include: path.resolve(ROOT_PATH, 'app'),
      },
      {
        test: /\.css$/,
        loaders: [
          'style',
          'css?modules&amp;importLoaders=1&amp;localIdentName=[name]__[local]___[hash:base64:5]',
          'sass?includePaths[]=' + SASS_DEPS,
          'postcss'
        ],
        include: path.resolve(ROOT_PATH),
        exclude: /(pure\/grids|Grids).*\.css$/,
      },
      {
        test: /(pure\/grids|Grids).*\.css$/,
        loaders: [
          'style',
          'css',
          'sass?includePaths[]=' + SASS_DEPS,
        ],
        include: path.resolve(ROOT_PATH),
      },
      {
        test: /\.woff(2)?(\?v=[0-9]\.[0-9]\.[0-9])?$/,
        loader: 'url-loader?limit=10000&amp;minetype=application/font-woff',
      },
      { test: /\.(ttf|eot|svg)(\?v=[0-9]\.[0-9]\.[0-9])?$/,
        loader: 'file-loader',
      },
      {
        test: /\.json$/,
        loader: 'json',
      },
    ],
  },
  plugins: [
    new HtmlWebpackPlugin({
      title: 'My App',
      template: path.resolve(ROOT_PATH, 'app/index.html'),
      inject: 'body',
      minify: {
        removeComments: true,
        collapseWhitespace: true,
      },
    }),
    new webpack.DefinePlugin({
      __DEV__: JSON.stringify(JSON.parse(process.env.BUILD_DEV || 'false')),
      __STAGING__: JSON.stringify(JSON.parse(process.env.BUILD_STAGING || 'false')),
      __API_HOST__: JSON.stringify(process.env.BUILD_STAGING ? 'my.api' : 'my.api'),
    }),
  ],
  resolve: {
    alias: {
      'styles': path.resolve(ROOT_PATH, 'app/styles'),
    },
    extensions: ['', '.js', '.jsx', '.json'],
  },
  postcss: function() {
    return [
      require('postcss-import'),
      require('autoprefixer'),
      require('postcss-cssnext'),
    ]
  }
};

if (TARGET === 'start' || !TARGET) {
  module.exports = merge(common, {
    output: {
      filename: '[hash].js',
      path: path.resolve(ROOT_PATH, 'build'),
      publicPath: '/',
    },
    devtool: 'eval-source-map',
    module: {
      loaders: [
        {
          test: /\.jsx?$/,
          loaders: [
            'react-hot',
            'babel-loader'
          ],
          include: path.resolve(ROOT_PATH, 'app'),
        },
      ],
    },
    devServer: {
      colors: true,
      historyApiFallback: true,
      hot: true,
      inline: true,
      progress: true,
    },
    plugins: [
      new webpack.HotModuleReplacementPlugin(),
    ],
  });
} else if (TARGET === 'build' || TARGET === 'builds') {
  const config = {
    resolve: {
      alias: {},
    },
    module: {
      loaders: [
        {
          test: /\.jsx?$/,
          loader: 'babel-loader',
          include: path.resolve(ROOT_PATH, 'app'),
        },
      ],
      noParse: [],
    },
    plugins: [
      new webpack.optimize.UglifyJsPlugin({
        minimize: true,
        compressor: {
          screw_ie8: true,
          warnings: false,
        },
        compress: {
          warnings: false,
        },
        output: {
          comments: false,
        },
      }),
      new webpack.optimize.DedupePlugin(),
      new webpack.DefinePlugin({
        'process.env': { 'NODE_ENV': JSON.stringify(process.env.NODE_ENV) },
      }),
    ],
  };
  deps.forEach((dep) =&gt; {
    const depPath = path.resolve(nodeModulesDir, dep);
    config.resolve.alias[dep.split(path.sep)[0]] = depPath;
    config.module.noParse.push(depPath);
  });
  module.exports = merge(common, config);
}
</code></pre>