计算属性的 getter 和 setter

  <div id="app">{{fullName}}</div>
  <script>
    var vm = new Vue({
      el: '#app',
      data: {
        firstName: '1',
        lastName: '2',
      },
      computed: {
      //注意：此时fullName是obj
        fullName: {
          get() {
            return this.firstName+' '+this.lastName
          },
         // set方法：通过设置的值改变相关联的值，又引起fullName的改变
          set(value) {
            let arr = value.split(' ')
            this.firstName = arr[0]
            this.lastName = arr[1]
          }  
        }
      }
    })