test.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>组合式API</title>
</head>
<body>
<div id="app">
  {{ count }}
  <button @click="add">加1</button>
</div>
</body>
<script>
  const { ref, onMounted } = Vue
  Vue.createApp({
    setup () {
      const count = ref(0)
      const add = () => {
        count.value += 1
      }
      onMounted(() => {
        console.log(1111)
      })
      return {
        count,
        add
      }
    },
    data () {
      return {
        count: 10
      }
    },
    methods: {
      add () {
        this.count += 10
      }
    },
    mounted () {
      console.log('2222')
    }
  }).mount('#app')
</script>
</html>