airbnb_clone/frontend/reducers/session_reducers.js

import {
    RECEIVE_CURRENT_USER,
    LOGOUT_CURRENT_USER,
} from '../actions/session_actions';

const _nullUser = Object.freeze({
    id: null
});

const sessionReducer = (state = _nullUser, action) => {
    Object.freeze(state);
    switch (action.type) {
        // case RECEIVE_CURRENT_USER:
        //     return { id: action.currentUser.id };
        case RECEIVE_CURRENT_USER:
            return { currentUserId: Object.values(action.currentUser.users)[0].id };
        case LOGOUT_CURRENT_USER:
            return _nullUser;
        default:
            return state;
    }
};

export default sessionReducer;