Markdium-React state update on an unmounted component

Markdium-JSX.jsx

const initialState = { loading: false, selectedPet: "", petData: null }

function petsReducer(state, action) {
  switch (action.type) {
    case "PET_SELECTED": {
      return {
        ...state,
        selectedPet: action.payload
      };
    }
    case "FETCH_PET": {
      return {
        ...state,
        loading: true,
        petData: null
      };
    }
    case "FETCH_PET_SUCCESS": {
      return {
        ...state,
        loading: false,
        petData: action.payload
      };
    }

    case "RESET": {
      return initialState;
    }

    default:
      throw new Error( `Not supported action ${action.type}` );
  }
}