How to unsubscribe a firestore snapshot listener when component will unmount?

Question

I am using React with Typescript and redux with the thunk layer. So, I defined one of my action as follows and it deals with a firestore snapshot listener.

export const getEmployees = () : ThunkAction<void, RootState, null, TableActions> => {

    const db = fire.firestore();

    return async dispatch => {
        db.collection("collection_name").get().then((querySnapshot) => {
            // body
        });
    }
};

and I dispatched it as following when a component will mount.

useEffect(() => {
   dispatch(getEmployees());
},[]);

So, my question is there any best way to unsubscribe the listener when a component will unmount?