title: React Component is not defined no-undef
body: <p>As a beginner, I am trying to render default react landing page from header.js into index.js.
  Please help me with an explanation where am I wrong
  Index.js - </p>
  
  <pre><code>import React from 'react';
  import ReactDOM from 'react-dom';
  import './header.css';
  import Header from './header';
  import registerServiceWorker from './registerServiceWorker';
  
  class App extends Component {
      render() {
        return (
          &lt;Header /&gt;
        );
      }
    }
  
  ReactDOM.render(&lt;App /&gt;, document.getElementById('root'));
  registerServiceWorker();
  </code></pre>
  
  <p>header.js - </p>
  
  <pre><code>import React from 'react';
  import ReactDOM from 'react-dom';
  import './header.css';
  import registerServiceWorker from './registerServiceWorker';
  
  class Header extends Component {
      render() {
        return (
          &lt;div className="App"&gt;
            &lt;header className="App-header"&gt;
              &lt;h1 className="App-title"&gt;Welcome to React&lt;/h1&gt;
            &lt;/header&gt;
            &lt;p className="App-intro"&gt;
              To get started, edit &lt;code&gt;src/App.js&lt;/code&gt; and save to reload.
            &lt;/p&gt;
          &lt;/div&gt;
        );
      }
    }
  </code></pre>
  
  <p>Error - </p>
  
  <pre><code>./src/index.js
    Line 7:  'Component' is not defined  no-undef
  </code></pre>