Does reducers added via combineReducers use Immer for state updates?

November 11, 2022

I am a complete newbie in using Redux/Redux Toolkit and am working on writing a small application.
My current store and reducer setup looks something like below:

const store = configureStore({
    reducer: rootReducer
})
  
...
...
const rootReducer = combineReducers({
    settings: SettingsReducer,
    user: UserReducer,
})

I have written SettingsReducer and UserReducer something like below:

const SettingsReducer = (state: SettingsState = initialSettingsState, action: SettingsReducerActionType) => {
    switch (action.type) {
        ...
        ...
        default: return state
    }
}

const UserReducer = (state: UserState = initialUserState, action: UserReducerActionType) => {
    switch (action.type) {
        ...
        ...
        default: return state
    }
}

I would like to know if my UserReducer and SettingsReducer will use Immer for updating state? Looking at the Redux documentation it mentions using functions createSlice and createReducer will allow Immer usage so I wanted to get some confirmation.

>Solution :

From Redux’s documentation

Redux Toolkit’s createReducer and createSlice automatically use Immer internally to let you write simpler immutable update logic using "mutating" syntax. This helps simplify most reducer implementations.

By not using createReducer and createSlice, you’re not using Immer.