Vue watch can't detect changes in objects in data? How do you write it?

data(){
    return{
        type:"1",
        yanxuan:"",
        qiugou:"",    
    }
}

if the data is like this, you can listen.

data(){
    return{
        parameter:{
            type:"1",
            yanxuan:"",
            qiugou:"",
        }
    }
}

Why can"t you listen when it"s written like this? How to write it. ,
solve?

watch:{
            parameter:function(){
                ...
            }
        },

if you write in this way, the data in param will not be changed. Watch will not execute
. Can you only write one data at a time?

Javascript vue.js

Jun.19,2021

https://cn.vuejs.org/v2/api/-sharp.
https://cn.vuejs.org/v2/api/-sharp.
option deep: true,watcher can detect changes within the object

watch: {
    //  watcher
    c: {
      handler: function (val, oldVal) { /* ... */ },
      deep: true
    }
  }

https://cn.vuejs.org/v2/api/-sharp.

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