demo/06/index.html

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Hello DOM</title>
  <script src="https://cdn.staticfile.org/react/16.4.0/umd/react.development.js"></script>
  <script src="https://cdn.staticfile.org/react-dom/16.4.0/umd/react-dom.development.js"></script>
  <script src="https://cdn.staticfile.org/babel-standalone/6.26.0/babel.min.js"></script>
</head>

<body>
  <div id="root"></div>

  <script type="text/babel">
    class MyComponent extends React.Component {
      constructor(props) {
        super(props);
        this.myTextFocus = React.createRef();
        this.handerClick = this.handerClick.bind(this);
      }
      handerClick() {
        this.myTextFocus.current.focus();
      }
      render() {
        return (
          <div>
            <input type="text" ref={this.myTextFocus} />
            <input type="button" value="点击聚焦" onClick={this.handerClick} />
          </div>
        );
      }
    }
    ReactDOM.render(
      <MyComponent />,
      document.getElementById('root')
    )
  </script>
</body>

</html>