Summary  
This chapter explains how to write reducers as simple mutating functions while relying on an underlying tool (Immer) to convert those changes into safe, immutable state updates automatically.

General domain of usage  
Application state management

Reducers define how state changes. In Redux Toolkit, reducers are written in a much simpler way compared to older Redux.





## Writing Reducers

Inside a slice, reducers look like regular functions:

```javascript
increment(state) {
  state.value += 1;
}
```

At first glance, it looks like you are modifying the state directly.





## Why This Works

In standard Redux, you are not allowed to change state directly. You had to return a new object every time.

Redux Toolkit uses a tool under the hood that lets you write simpler code while still keeping state updates safe.





## The Key Idea

You write reducers as if you are changing the state. Redux Toolkit takes care of turning those changes into safe updates.



Tutustu Redux Toolkitiin yhdessä Reactin kanssa ja tehosta tilanhallintataitojasi. Tämä kurssi esittelee kattavasti Redux Toolkitiin, tehokkaan kirjaston tilanhallintaan. Opit yksinkertaistamaan Reduxin käyttöönottoa, selkeyttämään monimutkaista tilalogiikkaa ja luomaan tehokkaita, skaalautuvia React-sovelluksia.

Understand why Redux Toolkit exists and when it becomes useful. Recognize how state complexity grows in real applications and why simple approaches stop scaling.

Install Redux Toolkit and set up the store. Connect Redux to a React application and understand how data flows through the system.

Define state using slices and organize logic clearly. Create reducers, use generated actions, and keep state manageable as the application grows.

Read data from the store using useSelector and update it with useDispatch. Structure state correctly and avoid common mistakes when working with shared data.

Fetch data from APIs using createAsyncThunk. Manage loading and error states and keep the UI in sync with async updates.

Split state into multiple slices and organize files by feature. Combine reducers cleanly and maintain a clear structure as the application grows.

Build a complete application using Redux Toolkit. Implement CRUD features, handle async data, and improve the user experience with loading and error states.

Writing Reducers the Simple Way

Writing Reducers

Why This Works

The Key Idea