Splitting and combining reducers

As your application grows, you probably wouldn't want to write all the logic for how the state of your application needs to be transformed in a simple reducer function. What you would probably want is to write smaller reducers that specialize in managing independent parts of the state.

Take for example the following reducer function:

const initialState = { 
    todoList: [], 
    chatMsg: [], 
} 
const reducer = (state = initialState, action) => { 
    switch (action.type) { 
        case 'ADD_TODO': return { 
            ...state, 
            todoList: [ 
                ...state.todoList, 
                { 
                    title: action.title, 
                    completed: action.completed, 
                }, 
            ], 
        } 
        case 'ADD_CHAT_MSG': return { 
            ...state, 
       ...