vue.js计算属性是什么？（代码示例）

<template>
  <ul>
   <li>First name : {{firstName}}</li>
   <li>Last name : {{lastName}}</li>
   <li>Full name : {{firstName + &#39; &#39;+ lastName}}</li>
  </ul>
</template>

<script>
 data:function(){
     return{
         firstName: "Sai",
         lastName: "Gowtham"
     }
 }
</script>

<template>
  <ul>
   <li>First name : {{firstName}}</li>
   <li>Last name : {{lastName}}</li>
   <!-- 计算属性 -->
   <li>Full name : {{fullName}}</li>
  </ul>
</template>

<script>
export default{
     data:function(){
     return{
         firstName: "Sai",
         lastName: "Gowtham"
     }
  },
  computed:{
      fullName:function(){
          return this.firstName+&#39; &#39;+this.lastName
      }
  }
}