关于vue中watch检测到不到对象属性的变化的解决方法

<template>
 <div>
  <dl>name: {{option.name}}</dl>
  <dl>age: {{option.age}}</dl>
  <dl>
   <button @click="updateAgeTo25">update age with 25</button>
  </dl>
 </div>
</template>

<script>
export default {
 data () {
  return {
   option: {
    name: "isaac",
    age: 24
   }
  }
 },
 watch: {
  option(val) {
   console.log(val)
  }
 },
 methods: {
  updateAgeTo25() {
   this.option.age = 25
  }
 }
}
</script>

 ...
 watch: {
  option: {
   handler(newVal) {
    console.log(newVal);
   },
   deep: true,
   immediate: true
  }
 },
 ...