Should Pinia warn when a mapState property is initially not present?

[rbanks54]

Quick scenario: Vue 2 with Options API, Typescript, Pinia 0.5.4

Assume I have a state defined as

export class MyState {
  currentId?: ReferenceId;
}

and define my store as

export const useMyStore = defineStore({
  id: 'myStore',
  state(): MyState { return new MyState() },
  actions: {
    setActiveReference(referenceId: ReferenceId){
      Vue.set(this,'currentId',referenceId);
    },
    //...
  }
}

and finally, I in my options API I use mapState() like so...

computed: {
  ...mapState(useMyStore, {
    activeReference: state => state.currentId,
//...

As far as I can tell, when the mapState() method is called, since the currentId property isn't present in the state object there won't be any subscription for change notifications created. activeReference will always be a non-reactive as a result.

Even once setActiveReference() is called, activeReference won't suddenly start being reactive because there's no way to indicate to the component that the currentId property now exists and change events can be subscribed to.

Since it's easy to miss explicitly setting undefined values in classes (at least, it was for me!) is it possible/worthwhile for Pinia to warn during the mapState() call if a keymapper function is referencing a property that doesn't actually exist?

[posva]

The problem here is that the return value of state should be a plain object, like data. Probably worth adding to the API docs. Maybe we could add a warning if the return isn't a plain object. There is already a function for it (I think it should work) in the code base !