菜鸟教程在线编辑器

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                <!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>菜鸟教程 React 实例</title>
<script src="https://lf26-cdn-tos.bytecdntp.com/cdn/expire-1-M/react/18.2.0/umd/react.production.min.js" ></script>
<script src="https://lf3-cdn-tos.bytecdntp.com/cdn/expire-1-M/react-dom/18.2.0/umd/react-dom.production.min.js"></script>
<script src="https://lf9-cdn-tos.bytecdntp.com/cdn/expire-1-M/babel-standalone/6.26.0/babel.min.js" ></script>
</head>
<body>
<div id="root"></div>
<script type="text/babel">
class Clock extends React.Component {
  constructor(props) {
    super(props);
    this.state = {date: new Date()};
  }

  componentDidMount() {
    this.timerID = setInterval(
      () => this.tick(),
      1000
    );
  }

  componentWillUnmount() {
    clearInterval(this.timerID);
  }

  tick() {
    this.setState({
      date: new Date()
    });
  }

  render() {
    return (
      <div>
        <h1>Hello, Runoob!</h1>
        <h2>现在时间是：{this.state.date.toLocaleTimeString()}.</h2>
      </div>
    );
  }
}

const root = ReactDOM.createRoot(document.getElementById("root"));
root.render(
  <Clock />
);
</script>

</body>
</html>
              