index.html

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="./js/render.js"></script>
  <script src="./js/mount.js"></script>
  <script src="./js/patch.js"></script>
  <script src="./js/reactive.js"></script>
  <script src="./js/createApp.js"></script>
</head>

<body>
  <div id="app"></div>

  <script>
    const App = {
      data: {
        obj: reactive({
          name: 'Tom',
          age: 999
        })
      },
      render() {
        return h('div', {}, this.data.obj.name)
      }
    }

    const app = createApp(App)
    app.mount('#app')

    setTimeout(() => {
      App.data.obj.name = 'Jerry'
    }, 2000)
  </script>
</body>

</html>