vue-watch

<template>
    <div>

        <!-- 监听值的改变： -->
        <button class="th" @click="add">添加</button>
        <input v-model="count" type="text">

    </div>
</template>

<script>
export default {
    data() {
       return {
       count:
      };
    },
methods: {
   add(){
  this.count++;
    }
    },
watch: {
count:function(new value,oldvalue){
   console.log("a的值是"+a)
  console.log("b的值是"+b)
    }
  }
};
</script>