Pinia: How to dynamically add new enteries to store state

[aliraza944]

I have a use case with the pinia in vue 3 that I want to dynamically add new entries to the pinia store using the store actions. for example if I have a state called firstName and if I call a the action of the store it should add new state called lastName in the state as well. Here is what I have tried

import { defineStore } from "pinia";

export const useAdvanceListingsFilterStore = defineStore(
  "advance-listing-filters",
  {
    state: () => {
      return {
        firstName: "jhon",
      };
    },
    actions: {
      setLastName(payload) {
        return {
          ...this.state,
          lastName: payload,
        };
      },
     
     
    },
  }
);

The new state should include the fistName and lastName fields.