Vue中对watch的理解(关键是immediate和deep属性)

watch: {
    被监听的数据: {
        handler(数据改变后的值, 数据改变之前的值) {
            相关代码逻辑...
        }
    }
}

<template>
  <div class="about">
    <!-- <h1>This is an about page</h1> -->
    <p>username:<input type="text" v-model="username"> {{username}}</p>
    <p>password:<input type="text" v-model="password"> {{password}}</p>
    <p>age:<input type="text" v-model="age"> {{age}}</p>
    <p>student.id:<input type="text" v-model="student.id"> {{student.id}}</p>
    <p>student.studentName:<input type="text" v-model="student.studentName"> {{student.studentName}}</p>
 
  </div>
</template>
<script>
export default {
  data(){
    return{
      username:'lijiang',
      password:'123',
      age:21,
      student:{
        id:1,
        studentName:'李疆'
      }
    }
  },
  methods:{
     Test:function(newValue,oldValue){
           console.log('newValue:%s,oldValue:%s',newValue,oldValue);
     }
  },
  watch:{
    username:function(newValue,oldValue){
      console.log('username newValue:'+newValue+',username oldValue:'+oldValue);
    },
 
    password:'Test',
 
    age:{
      handler:function(newValue,oldValue){
        console.log('age newValue:'+newValue+',age oldValue:'+oldValue);
      },
      immediate:true //第一次刷新页面时就会执行
    },
 
    student:{
      handler:function(newValue,oldValue){
        console.log('student newValue.id:'+newValue.id+',student oldValue:'+oldValue);
      },
      immediate:true,
      deep:true
    },
    
    'student.studentName':'Test'
  }
}
</script>