title: Webpack-dev-server injects bundle in HTML page, but nothing is rendered
body: <p>When I run webpack-dev-server (Command: "webpack-dev-server --mode development --open --progress --hot"), my bundle is injected into the html page, but nothing is rendered.</p>
  
  <p>Webpack.config.js file:</p>
  
  <pre><code>var path = require('path');
  var HtmlWebpackPlugin = require('html-webpack-plugin');
  module.exports = {
      devtool: "cheap-eval-source-map",
      entry: path.join(__dirname, 'src', 'App.js'),
      output: {
          path: path.join(__dirname, 'dist'),
          filename: "bundle.js"
      },
      module: {
          rules: [
              {
                  test: /\.js$/,
                  loader: 'babel-loader',
                  include: path.join(__dirname, 'src')
              }
          ]
      },
      devServer: {
          contentBase: path.join(__dirname, 'dist'),
          inline: true
      },
      plugins: [
          new HtmlWebpackPlugin({
              template: path.join(__dirname, 'src', 'index.html'),
              hash: true,
          })
      ]
  }
  </code></pre>
  
  <p>Index.js file:</p>
  
  <pre><code>import React from 'react';
  import ReactDOM from 'react-dom';
  import App from './App';
  
  ReactDOM.render(&lt;App /&gt;, document.getElementById('app'));
  </code></pre>
  
  <p>App.js file:</p>
  
  <p>import React from 'react';</p>
  
  <pre><code>export default class App extends React.Component {
      render() {
          return (
              &lt;div className="container"&gt;
                  &lt;h1&gt;React Starter App&lt;/h1&gt;
              &lt;/div&gt;
          );
      }
  }
  </code></pre>
  
  <p>The thing is if I change App.js to:</p>
  
  <pre><code>alert("test");
  </code></pre>
  
  <p>It will display the alert on the page.</p>