watch监听对象时

     data: {
        obj: {
            num: 1
        },
    },
watch: {
     obj: {
         handler: function(newv,oldv) {

         },
         deep: true
     }
     //或者
         obj.num': {
            handler(newol, old) {
                console.log(newol, old)
            },
            deep: true,
        }
}