title: Reactjs TypeError: Class extends value undefined is not a constructor or null
body: <p>Actually I have just started learning react. I'm taking tutorials from websites. but when I compiled my this code in command line it says "Compiled Successfully" but when I open the browser it says </p>
  
  <blockquote>
    <p>"TypeError: Class extends value undefined is not a constructor or null" </p>
  </blockquote>
  
  <p>Actually I don't know how to fix this issue. But due to this error I'm unable to continue my course. </p>
  
  <pre><code>import React, {component} from 'react';
  import CardList from './CardList';
  import {robots} from './robots';
  import SearchBox from './SearchBox';
  
  class App extends component {
      constructor(){
          super()
          this.state = {
          robots: robots,
          searchfield: ''     
          }
      }
      onSearchChange(event) {
          console.log(event.target.value);
      }
      render () {
      return (
          &lt;div className='tc'&gt;
          &lt;h1&gt; RoboFriends &lt;/h1&gt;
          &lt;SearchBox searchChange={this.onSearchChange}/&gt;
          &lt;CardList robots ={this.state.robots}/&gt;
          &lt;/div&gt;
          );
      }
   }  
  
  export default App;
  </code></pre>