点击 changeName 或者 changeAge，都会触发 watch user 的 handler，怎么知道具体是哪个函数触发了 watch user 的 handler 呢？

<template>
  <div>
    <button @click="changeName">change name</button>
    <button @click="changeAge">change age</button>
  </div>
</template>

<script>
export default {
  methods: {
    changeName() {
      this.user.name = 'bar';
    },
    changeAge() {
      this.user.name = 20;
    }
  },
  data() {
    return {
      user: {
        name: "foo",
        age: 18
      }
    }
  },
  watch: {
    user: {
      deep: true,
      handler() {
        debugger;
        console.log('user change');
      }
    }
  }
}
</script>