Dynamic Updates drop-down list of issues iview

Why 80% of the code can not do farming architect? >>>  

<template>
<div>
<Select v-model="selectuser" filterable label-in-value style="width:200px" >
  <Option v-for="item in userList" :value="item.id" :key="item.id">{{ item.username }}</Option>
</Select>
</div>
</template>

<script>
export default {
 data(){
  return {
   userList: [{
     id: 1,
     username: 'test'
   }],
   selectuser: 0,
  }
 },
 mounted(){
  setInternal(()=>{
   this.userList = [{
     id: 2,
     username: 'test2'
   }]
   setTimeout(()=>{
    this.selectuser = this.userList[0].id
   })
  },1000)
 },
 watch: {
  selectuser(){
   console.log('附新值', newVal)
  }
 }
}
</script>

When the dynamic drop-down list userList assigned to iview, v-model binding value selectuser at watch, if there is the original value, will first assignment is undefined

 

Reproduced in: https: //my.oschina.net/fyzhu/blog/3058894