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React Native Academy · Lección

Creación de slices con createSlice

Defina un slice con createSlice, declare el estado inicial y las funciones reducer, y exporte los action creators generados automáticamente y el reducer.

Creación de slices con createSlice es una lección gratuita de React Native Academy en CoddyKit. Esta es la lección 2 de 4. Puedes leer la lección completa abajo gratuitamente — luego la practicas en el navegador con un editor de código integrado y un tutor de IA 24/7. Forma parte de la ruta de aprendizaje de React Native Academy, y tu progreso se sincroniza en la web y la app de CoddyKit. El curso de React Native Academy incluye 4 lecciones en total.

Partes de esta lección aún no han sido traducidas y se muestran en inglés.

What Is a Redux Slice?

A slice is a self-contained piece of Redux logic for one feature of your app. It bundles the initial state, the reducer functions, and the auto-generated action creators together in a single file. The name comes from the idea that each slice represents a portion (slice) of the global Redux state tree.

Importing and Calling createSlice

createSlice is imported from @reduxjs/toolkit and accepts a configuration object with three required fields: name (a string prefix for action types), initialState (the starting value for this slice's state), and reducers (an object of reducer functions). It returns an object containing the slice reducer and the action creators.

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

const counterSlice = createSlice({
  name: 'counter',
  initialState: { value: 0 },
  reducers: {},
});

export default counterSlice.reducer;

Defining Reducer Functions

Each function you add to the reducers object becomes a case reducer that handles a specific action. RTK uses the Immer library under the hood, so you can write code that appears to mutate state directly — Immer converts it to an immutable update automatically. You never need to spread or copy the state object manually.

const counterSlice = createSlice({
  name: 'counter',
  initialState: { value: 0 },
  reducers: {
    increment(state) {
      state.value += 1; // Immer makes this safe
    },
    decrement(state) {
      state.value -= 1;
    },
    incrementByAmount(state, action) {
      state.value += action.payload;
    },
  },
});

Auto-Generated Action Creators

createSlice automatically generates an action creator for each reducer function you define. You export them from the slice and call them when dispatching. The action creator name matches the reducer key, and the generated action type string follows the pattern sliceName/reducerName, for example counter/increment.

export const { increment, decrement, incrementByAmount } = counterSlice.actions;

// Using in a component:
import { useAppDispatch } from '../../store/hooks';
import { increment } from './counterSlice';

const dispatch = useAppDispatch();
dispatch(increment());          // { type: 'counter/increment' }
dispatch(incrementByAmount(5)); // { type: 'counter/incrementByAmount', payload: 5 }

Exporting the Reducer

The createSlice call returns an object with a reducer property. You export this as the default export and then import it in your store configuration. RTK composes all your slice reducers into the single root reducer automatically when you pass them to configureStore.

// counterSlice.ts
const counterSlice = createSlice({ /* ... */ });
export const { increment, decrement } = counterSlice.actions;
export default counterSlice.reducer;

// store/index.ts
import counterReducer from '../features/counter/counterSlice';
export const store = configureStore({
  reducer: { counter: counterReducer },
});

Defining TypeScript State Types

When using TypeScript, explicitly type your initialState so RTK can infer state and action types throughout the slice. Define an interface for your state and assign it as the type annotation on initialState. RTK will then infer the correct type for the state parameter in every reducer function automatically.

interface CounterState {
  value: number;
  status: 'idle' | 'loading' | 'failed';
}

const initialState: CounterState = {
  value: 0,
  status: 'idle',
};

const counterSlice = createSlice({
  name: 'counter',
  initialState,
  reducers: {
    increment(state) {
      state.value += 1; // TypeScript knows state is CounterState
    },
  },
});

Using PayloadAction for Typed Payloads

When a reducer receives data from the dispatched action, import PayloadAction from RTK to type the action parameter. PayloadAction<number> tells TypeScript that action.payload must be a number. This prevents accidental mismatches between what the action creator accepts and what the reducer expects.

import { createSlice, PayloadAction } from '@reduxjs/toolkit';

const counterSlice = createSlice({
  name: 'counter',
  initialState: { value: 0 },
  reducers: {
    incrementByAmount(state, action: PayloadAction<number>) {
      state.value += action.payload;
    },
  },
});

The prepare Callback

The prepare callback lets you customize the action creator before RTK dispatches the action. You use it when you need to generate an ID, format data, or add a timestamp to the payload. The object returned by prepare must have a payload field, and optionally meta and error fields.

import { nanoid } from '@reduxjs/toolkit';

const todosSlice = createSlice({
  name: 'todos',
  initialState: [],
  reducers: {
    addTodo: {
      reducer(state, action: PayloadAction<{ id: string; text: string }>) {
        state.push(action.payload);
      },
      prepare(text: string) {
        return { payload: { id: nanoid(), text } };
      },
    },
  },
});

Resetting and Replacing State

Sometimes you need to reset a slice to its initial state — for example on user logout. You can return a completely new state value from a reducer instead of mutating. If you return a value, Immer uses it as the next state. This is the correct pattern for resetting or fully replacing state in a slice reducer.

const counterSlice = createSlice({
  name: 'counter',
  initialState: { value: 0, status: 'idle' },
  reducers: {
    reset() {
      // Return the fresh initial value instead of mutating
      return { value: 0, status: 'idle' };
    },
  },
});

Responding to Actions from Other Slices

Slices can respond to actions defined in other slices using extraReducers. This avoids tight coupling — instead of importing one slice into another, you import only the action creator. Use the builder.addCase pattern to handle external action types inside your slice without adding them to the reducers key.

import { userSlice } from '../user/userSlice';

const cartSlice = createSlice({
  name: 'cart',
  initialState: { items: [] },
  reducers: { /* own actions */ },
  extraReducers: (builder) => {
    builder.addCase(userSlice.actions.logout, (state) => {
      state.items = []; // clear cart when user logs out
    });
  },
});

Complete Counter Slice Example

Here is a complete, production-ready counter slice combining everything covered so far: a typed state interface, typed action creators with PayloadAction, and a reset action. Import this reducer into configureStore and its actions into components to have a fully working Redux feature.

import { createSlice, PayloadAction } from '@reduxjs/toolkit';

interface CounterState { value: number; }
const initialState: CounterState = { value: 0 };

export const counterSlice = createSlice({
  name: 'counter',
  initialState,
  reducers: {
    increment: (state) => { state.value += 1; },
    decrement: (state) => { state.value -= 1; },
    incrementByAmount: (state, action: PayloadAction<number>) => {
      state.value += action.payload;
    },
    reset: () => initialState,
  },
});

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

Quick Check

Test your understanding of React Native Mobile Development concepts from this lesson.

Lesson Recap

In this lesson you learned: createSlice bundles initial state, reducers, and action creators together, Immer lets you write mutating-style reducer code that stays immutable, and PayloadAction types the action payload for TypeScript safety. Next up we explore reading state with useSelector.

Preguntas frecuentes

¿La lección «Creación de slices con createSlice» es gratis?

Sí — el texto completo de «Creación de slices con createSlice» es gratis para leer aquí en la web. Para practicarla de forma interactiva (editor de código integrado y tutor de IA 24/7) y desbloquear el resto del curso de React Native Academy, actualiza a CoddyKit PRO. El curso de React Native Academy incluye 4 lecciones en total.

¿Qué aprenderé en «Creación de slices con createSlice»?

Defina un slice con createSlice, declare el estado inicial y las funciones reducer, y exporte los action creators generados automáticamente y el reducer. Practicas React Native Academy con código real que ejecutas directamente en el navegador, y un tutor de IA 24/7 responde tus preguntas mientras trabajas en la lección.

¿Necesito experiencia previa para empezar React Native Academy?

No se requiere experiencia previa. React Native Academy en CoddyKit está estructurado para principiantes hasta estudiantes avanzados, así que puedes empezar aquí o desde el inicio y avanzar a tu ritmo. Esta es la lección 2 de 4.

¿Cuánto tiempo toma la lección «Creación de slices con createSlice»?

La mayoría de las lecciones de CoddyKit toman alrededor de 5–10 minutos. Cada una es compacta e interactiva, así que avanzas constantemente y retomas exactamente por donde dejaste en la web y la app.

¿Puedo escribir y ejecutar código en esta lección de React Native Academy?

Sí. Cada lección de React Native Academy incluye un editor de código integrado, así que escribes y ejecutas código real directamente en tu navegador y obtienes retroalimentación instantánea de IA — sin configuración local necesaria.

Todas las lecciones de este curso

  1. Configuración del store y Provider de Redux
  2. Creación de slices con createSlice
  3. Lectura del estado con useSelector
  4. Thunks asíncronos con createAsyncThunk
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