vue中setup里面使用计算属性computed```js```计算属性里面是一个箭头函数作为参数计算属性里面是一个箭

<!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="https://unpkg.com/vue@next"></script>
  </head>
  <body>
    <div id="root"></div>
  </body>
  <script>
    const app = Vue.createApp({
      // setup
      setup() {
        const { ref, computed } = Vue;
        let count = ref("111");
        const handleAdd = () => {
          count.value++;
        };
        // 使用计算属性,来定义这个变量，计算属性里面是一个箭头函数作为参数
        // 写在函数里面的要return出去
        const countMultiplyTwo = computed(() => {
          return count.value * 2;
        });
        // 所有setup里面定义的都要返回出去
        return {
          count,
          handleAdd,
          countMultiplyTwo,
        };
      },
      // 模板
      template: `
        <h1 @click="handleAdd">{{count}}---->{{countMultiplyTwo}}</h1>
        
        `,
    });
    const vm = app.mount("#root");
  </script>
</html>