Redux has the problem that (a) the read-only reducer concept is totally at odds with how a bunch of JS builtins work and so conceptually hard to understand for a newbie, (b) it has just so much boilerplate for "best practices" for even the simplest use case, and (c) it's not immediately clear what the benefits of wrapping your head around all that are.

For me, it took me a while of working on a web app with derived data everywhere (~15 KB raw JSON that gets updated with diffs and recombobulated into different output formats and different intersections of data with live updates), and endless debugging of data transformations by stepping back and forth through the reducer history, before I really "got" it.

On the note of (b), I really like the redux-actions project (https://redux-actions.js.org) for the way its helpers that get rid of most of that. A simple example:

    const setValueA = createAction('SET_VALUE_A');
    const setValueB = createAction('SET_VALUE_B');
    const setValueAB = createAction('SET_VALUE_AB', (a, b) => ({ a, b }));

    export const reducer = combineReducers({
        valueA: handleActions({
            [setValueA]: (state, action) => action.payload
            [setValueAB]: (state, action) => action.payload.a
        }, null),

        valueB: handleActions({
            [setValueB]: (state, action) => action.payload
            [setValueAB]: (state, action) => action.payload.b
        }, null)
    });