Learning Redux

Defining the initial state

Now, we need to think about the state object of the undoable higher-order reducer. You may think that it would be easier to simply store the history in local variables in the function. If we did that, we could retain the state structure in our enhanced reducer, and we would not need to adjust our application to access the state using state.history[state.currentState].

However, as we discussed earlier, we should not cause side effects that affect the calculated state of the reducer. This also applies to higher-order reducers. This is why we need to store all undo/redo data in the Redux state, not just in a local variable. If we did store the state in a local variable, it would cause unpredictable behavior when combining ...