SOURCE

var app3 = new Vue({
  el: '#app',
  data: {
    seen: false,
    tempTotalPrice: null,
    totalPrice: 0,
  },
  computed: {
    totalPrice :{
      get() {
        if(this.tempTotalPrice){
          console.log('get tempTotalPrice');
          return this.tempTotalPrice;
        }
        
      },
      set(val) {
        this.tempTotalPrice = val;
      }
    }
  },
  methods:{
    getTemp(){
      console.log('getTemp');
    }
  }
})

<div id="app">
  <p v-if="seen">现在你看到我了</p>{{totalPrice}}
  <input type="button" @click="getTemp" size="4" value="getTemp" width="100"/>
</div>