pageData is an object, passed from my parents, and I received pageData, through props in the child component. I want to use watch to listen for changes in the properties in the pageData object, and then assign a value to newpageData.

but normal snooping pageData, doesn"t trigger at all. After changing it to deep surveillance. Console.log (newval) can listen for the latest value of pageData. Then I made a mistake when I tried to assign a value to this.newpageData.

* * Error in callback for watcher "pageData"
newpageData is not defined**

is there any way to solve this problem?

props:["pageData"],
data(){
    return{
       newpageData:null
    }
},
  watch:{
       pageData:{
                handler: function (newval, oldVal) {
                    console.log(newval)
                    this.newpageData=newval;
                },
                deep: true
            }
        }