html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<div id="root"></div>
<div id="app"></div>
<!-- 添加依赖 -->
<!-- 依赖三个包 -->
<!-- CDN引入 -->
<script crossorigin src="https://unpkg.com/react@18/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@18/umd/react-dom.development.js"></script>
<!-- babel -->
<script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
<!-- 下载引入 -->
<!-- npm下载引入（脚手架） -->
<script type="text/babel">
//编写React代码（jsx语法)
//jsx语法 -> 普通的JavaScript代码 - > babel
//渲染Hello world
//React18之前：ReactDOM.render
// ReactDOM.render(<h2>Hello World</h2>,document.querySelector("#root"));
//React18之后
const root = ReactDOM.createRoot(document.querySelector("#root"))
root.render(<h2>Hello World</h2>)
const app = ReactDOM.createRoot(document.querySelector("#app"))
app.render(<h2>你好啊，李银河</h2>)
</script>
</body>
</html>