Nuxtjs如何使用观察者查找在v-for中更改的索引

我有一个示例代码,其中filteredDates是范围日期,timeOptionsByDate是范围从18:00到00:00

<tr v-for="(date, index) in filteredDates" :key="date">
   <select v-model="formData.office_hour[index].time_from">
      <option v-for="time in timeOptionsByDate(date)" :value="time" :key="time">{{ time }}</option>
   </select>
   <select v-model="formData.office_hour[index].time_to">
      <option v-for="time in timeOptionsByDate(date)" :value="time" :key="time">{{ time }}</option>
   </select>
</tr>

论观察者

watch: {
   'formData.office_hour': {
      deep: true,
      handler: 'handleOfficeHourChange',
    },
}

方法论

handleOfficeHourChange(newVal, oldVal) {
   const index = this.findChangedIndex(newVal, oldVal)
},
findChangedIndex(newVal, oldVal) {
   for (let i = 0; i < newVal.length; i++) {
      if (!this.isEqual(newVal[i], oldVal[i])) {
         return i;
      }
   }
   return -1;
},

当我选择time_from时,time_to总是-1,错误的索引已经更改,如何更正上面的表达式