Redux reducers — changing deeply-nested state

You can definitely have reducers inside of reducers; in fact, the redux demo app does this: http://redux.js.org/docs/basics/Reducers.html.

For example, you might make a nested reducer called `discounts’:

function discounts(state, action) {
    switch (action.type) {
        case ADD_DISCOUNT:
            return state.concat([action.payload]);

        // etc etc
    }
}

And then make use of this reducer in your account reducer:

function account(state, action) {
    switch (action.type) {
        case ADD_DISCOUNT:
            return {
                ...state,
                discounts: discounts(state.discounts, action)
            };

         // etc etc
    }
}

To learn more, check out the egghead.io redux series by Dan himself, specifically the reducer composition video!