2. ref 创建响应式数据(2.x的data)

<template>
  <div style="margin: 30px">
    <p>
    {{count}} 
  </p>
  <ol>
      <li v-for="(item,index) in list" :key="index">{{item}}</li> 
   </ol>
  </div>
</template>
<script> 
import {ref} from 'vue';
export default { 
  setup(props) {
    const count = ref(0); 
    const list = ref(['a','b','c']);
    return {
      count,
      list
    };
  },
};
</script>