Accessing other parts of the state, when using combined reducers

Question

NB: This is a question, very similar to Redux; accessing other parts... but it has nothing to do with Router :( thus cannot be solved same way

When I reduce one part of the state, I "feel" like I need to access other parts as well. I admit that I just might "misfeel" the core principals of the Redux, or have flaws in my app's architecture.

My current solution would be to modify github:combineReducers.js's code:

var finalState = mapValues(finalReducers, (reducer, key) => {
   var previousStateForKey = state[key]
   var nextStateForKey = reducer(previousStateForKey, action)
   ...
}

from

   var nextStateForKey = reducer(previousStateForKey, action)

to

   var nextStateForKey = reducer(previousStateForKey, action, state)

which would allow me to do what I need:

function reducer(state, action, root) {
   if (root.otherPart.get("isSomething")) {
      return state.set("anotherThing", true);
   }
   return state;
}

Question is if I am on the right way to do it, or is it something that should be solved using different architectural approaches, without having a need to access one part of state from other parts?

** UPDATE 5h Dec, 2018 **

Due to relatively high interest to this question (15 up-votes atm), I am adding my own answer below, hope it helps to those who is looking for that answer.

Answer 1

You don't have to use combineReducers().

From the official Redux docs:

This helper is just a convenience! You can write your own combineReducers that works differently, or even assemble the state object from the child reducers manually and write a root reducing function explicitly, like you would write any other function.

You may call combineReducers at any level of the reducer hierarchy. It doesn’t have to happen at the top. In fact you may use it again to split the child reducers that get too complicated into independent grandchildren, and so on.

So your proposed solution is definitely one way you can do it.

Thanks to @MichelleTilley for spearheading the train of thought!

Answer 2

I use Thunk to getState(), prepare the data from the full store, then dispatch an action.

You can put the decision logic in the reducer or in the action. It is up to you. I prefer fat actions and thin reducers but there is no right/wrong.

Leonardo