title: onKeyUp not working in React where onChange did
body: <p>I'm doing a React coding challenge that requires a value to be updated onKeyUp. I initially set it to update onChange but the tests require onKeyUp so I tried to change it to that, but my fields are no longer updating and I can't type anything into the textarea.</p>
  
  <pre><code>class MarkdownApp extends React.Component {
    constructor(props) {
      super(props);
      this.state = {
        value: ''
      };
  
      this.handleKeyUp = this.handleKeyUp.bind(this);
    }
  
    handleKeyUp(event) {
      this.setState({ value: event.target.value })
    }
  
    render() {
      return (
        &lt;form&gt;
          &lt;label&gt;
            Enter your markdown here:
            &lt;br /&gt;
            &lt;textarea value={this.state.value} onKeyUp={this.handleKeyUp} id='editor' /&gt;
            &lt;br /&gt;
          &lt;/label&gt;
          &lt;label&gt;
            Your markup will be previewed here:
            &lt;p id='preview'&gt;{marked(this.state.value)}&lt;/p&gt;
          &lt;/label&gt;
        &lt;/form&gt;
      );
    }
  }
  
  ReactDOM.render(
    &lt;MarkdownApp /&gt;,
    document.getElementById('root')
  );
  </code></pre>
  
  <p>Like I said, this worked fine when it was onChange and my function was handleChange, but since I switched it I can't type anything.</p>