详解Vue的watch中的immediate与watch是什么意思

data() {
   return {
    value:''
   };
  },
  watch:{
   value:{
    handler:'init',
    immediate:true
   }
  },
  methods: {
   init(){
    alert(1)
   }
  }

<div>
  <input type="text" v-model="student.studentName">{{student.studentName}}
 </div>
 

student:{
     studentName:'xi'
    }

watch:{
  student:{
    handler:function (newValue,oldValue) {
     console.log(newValue,'new')
     console.log(oldValue,'old')
    },
     deep:true,
     immediate:true
   }

}