SOURCE

new Vue({
  el:'#app',
  
  data:{
    count:0,
    count1:0
  },
//   数据：函数，当数据发生变化时调用函数，数据的值为函数的第一参数。
  watch:{
    count: function(val){
       console.log(val);
    }
  },
        
  methods:{
    getCount:function(){
      console.log('in');
      return this.count>5 ? '大于5' : '小于5';
    },
    countIncrease:function(){
      this.count++;
    },
    countDe:function(){
      this.count--;
    }
  }
  
})

<script src="https://cdn.jsdelivr.net/npm/vue"></script>
<div id="app">
  <button @click='countIncrease'>count + 1</button>
  <button @click='countDe'>count - 1</button>
  <button @click='count1++'>count1 + 1</button>
  <p>count: {{ count }}</p>
  <p>count1: {{ count1 }}</p>
</div>