[Vuejs]-Watch a property that can be undefined / default value for nested watch property

you can use a created/mounted lifecycle hook, to set the default value there first, and then if the value changes, it the watcher will react.

I suggest that you can set the default value of wheel when updating car data in VueStore.

Btw, It would be better to use { deep: true } property to watch data from computed in your code example.