Summary  
This chapter explains how to use Redux Toolkit’s createSlice function to define a piece of application state, its initial value, and reducer functions, automatically generating corresponding actions and a reducer.  

General domain of usage  
State management in front-end applications

A slice is created using the `createSlice` function. This is where you define your state and how it can change.



## Creating a Slice

Create a new file, for example:

```bash
src/features/counter/counterSlice.js
```

Inside this file, define your slice:

```javascript
import { createSlice } from '@reduxjs/toolkit';

const initialState = {
  value: 0
};

const counterSlice = createSlice({
  name: 'counter',
  initialState,
  reducers: {
    increment(state) {
      state.value += 1;
    },
    decrement(state) {
      state.value -= 1;
    }
  }
});

export const { increment, decrement } = counterSlice.actions;
export default counterSlice.reducer;
```

You define a piece of state and the logic that updates it.

`createSlice` automatically creates:

* Actions based on your reducers;
* A reducer function for the store;
* A structured way to manage this part of state.


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.

Creating Your First Slice with createSlice

Creating a Slice