ustk-todolist/client/src/middleware/keepSynced.js

import { REQUEST_LISTS, INVALIDATE_LISTS } from "../actions/defs";
import { fetchLists } from "../actions/lists";

export default (store) => (next) => (action) => {
    next(action);
    if (action.type !== REQUEST_LISTS && typeof action !== "function") {
        const state = store.getState();
        if (state.user.user) {
            const dirtyLists = state.lists.dirty || false;
            const dirtyTodos = state.todos.dirty || false;
            const fetchingLists = state.lists.fetching || false;
            if (
                ((dirtyLists || dirtyTodos) && !fetchingLists) ||
                action.type === INVALIDATE_LISTS
            ) {
                store.dispatch(fetchLists());
            }
        }
    }
};