Async Thunks with createAsyncThunk
Fetch data from an API inside a createAsyncThunk, handle the pending/fulfilled/rejected lifecycle in the slice's extraReducers, and display async status in the UI.
Async Thunks with createAsyncThunk is a free React Native Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the React Native Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why Do We Need Async Thunks?
Redux reducers must be pure synchronous functions — they cannot make API calls or run async code. To fetch data from a server and store the result in Redux, we need an async thunk: a function that dispatches plain actions before and after an async operation. Redux Toolkit's createAsyncThunk handles this pattern with minimal boilerplate.
Creating an Async Thunk
createAsyncThunk accepts two arguments: a string action type prefix and a payload creator function that performs the async work and returns the result. It automatically dispatches pending, fulfilled, or rejected actions based on whether the payload creator's promise resolves or rejects.
import { createAsyncThunk } from '@reduxjs/toolkit';
import axios from 'axios';
export const fetchPosts = createAsyncThunk(
'posts/fetchPosts', // action type prefix
async (page: number) => { // payload creator
const response = await axios.get('https://api.example.com/posts?page=' + page);
return response.data; // this becomes action.payload
}
);The Three Lifecycle Actions
For every createAsyncThunk call, RTK automatically creates three action creators: thunk.pending (dispatched when the async call starts), thunk.fulfilled (dispatched with the returned data when it succeeds), and thunk.rejected (dispatched with the error when it fails). You handle each case in extraReducers.
// These are created automatically:
fetchPosts.pending.type // 'posts/fetchPosts/pending'
fetchPosts.fulfilled.type // 'posts/fetchPosts/fulfilled'
fetchPosts.rejected.type // 'posts/fetchPosts/rejected'Handling Lifecycle in extraReducers
Use the builder.addCase pattern inside extraReducers to handle each lifecycle action. In the pending case set a loading flag, in fulfilled store the data and clear loading, and in rejected store the error message and clear loading. This gives every async operation a consistent state machine.
const postsSlice = createSlice({
name: 'posts',
initialState: { items: [], status: 'idle', error: null },
reducers: {},
extraReducers: (builder) => {
builder
.addCase(fetchPosts.pending, (state) => {
state.status = 'loading';
})
.addCase(fetchPosts.fulfilled, (state, action) => {
state.status = 'succeeded';
state.items = action.payload;
})
.addCase(fetchPosts.rejected, (state, action) => {
state.status = 'failed';
state.error = action.error.message ?? 'Unknown error';
});
},
});Dispatching an Async Thunk from a Component
Dispatch an async thunk exactly like a regular action — pass it to dispatch(). The thunk returns a Promise, so you can await it or chain .then() if you need to react after the async operation completes inside the component. Use useEffect to dispatch it on mount.
import { useEffect } from 'react';
import { useAppDispatch, useAppSelector } from '../../store/hooks';
import { fetchPosts } from './postsSlice';
export default function PostsScreen() {
const dispatch = useAppDispatch();
const { items, status, error } = useAppSelector((s) => s.posts);
useEffect(() => {
dispatch(fetchPosts(1));
}, [dispatch]);
if (status === 'loading') return <ActivityIndicator />;
if (status === 'failed') return <Text>{error}</Text>;
return <FlatList data={items} /* ... */ />;
}Passing Arguments to the Thunk
The payload creator function receives the first argument passed to the thunk when dispatched, and a second argument called thunkAPI that provides getState, dispatch, rejectWithValue, and more. Use getState to read current Redux state inside the thunk, for example to include an auth token in a request header.
export const createPost = createAsyncThunk(
'posts/create',
async (postData: { title: string; body: string }, thunkAPI) => {
const state = thunkAPI.getState() as RootState;
const token = state.user.token;
const response = await axios.post('/posts', postData, {
headers: { Authorization: 'Bearer ' + token },
});
return response.data;
}
);Handling Errors with rejectWithValue
By default, the rejected action contains only the serialized error message. If you need to pass a custom error payload — such as an HTTP status code or server-provided error message — use thunkAPI.rejectWithValue() inside a try-catch block. The value you pass becomes action.payload in the rejected case.
export const fetchUser = createAsyncThunk(
'user/fetch',
async (userId: string, { rejectWithValue }) => {
try {
const response = await axios.get('/users/' + userId);
return response.data;
} catch (err: any) {
return rejectWithValue(err.response.data.message);
}
}
);
// In extraReducers:
.addCase(fetchUser.rejected, (state, action) => {
state.error = action.payload as string; // custom error message
})Unwrapping the Dispatch Result
Dispatching a thunk returns a special Promise that you can unwrap() to get the fulfilled value or throw the error. This is useful when you need the result directly in the component — for example, navigating to a new screen after a successful API call without storing transient navigation state in Redux.
async function handleSubmit() {
try {
const result = await dispatch(createPost({ title, body })).unwrap();
navigation.navigate('PostDetail', { id: result.id });
} catch (err) {
Alert.alert('Error', 'Failed to create post');
}
}Cancelling an In-Flight Request
createAsyncThunk supports request cancellation via an AbortController. The thunkAPI.signal is an AbortSignal that you can pass to Axios or Fetch. When the component unmounts or the user navigates away, calling the thunk's abort() method cancels the pending request and dispatches the rejected action with AbortError.
export const fetchData = createAsyncThunk(
'data/fetch',
async (_, { signal }) => {
const response = await axios.get('/data', { signal });
return response.data;
}
);
// In component useEffect:
useEffect(() => {
const promise = dispatch(fetchData());
return () => promise.abort(); // cancel on unmount
}, []);Status-Driven UI Patterns
The status field in your slice state acts as a state machine with four values: idle, loading, succeeded, and failed. Pattern-match on this value in your component to show the right UI for each state. This prevents showing stale data and empty lists simultaneously, giving users clear feedback throughout the async lifecycle.
function renderContent() {
switch (status) {
case 'idle':
return <Text>Press button to load</Text>;
case 'loading':
return <ActivityIndicator size='large' />;
case 'succeeded':
return <FlatList data={items} renderItem={renderItem} />;
case 'failed':
return <Text style={styles.error}>{error}</Text>;
}
}Multiple Thunks for CRUD Operations
Real apps typically need separate thunks for each HTTP verb. Create one thunk per operation — fetchItems, addItem, updateItem, deleteItem — and handle each in extraReducers. After a successful mutation, update the local items array in the fulfilled handler so the UI stays in sync without re-fetching the entire list.
.addCase(deleteItem.fulfilled, (state, action) => {
state.items = state.items.filter((item) => item.id !== action.payload);
})
.addCase(addItem.fulfilled, (state, action) => {
state.items.push(action.payload);
})
.addCase(updateItem.fulfilled, (state, action) => {
const index = state.items.findIndex((i) => i.id === action.payload.id);
if (index !== -1) state.items[index] = action.payload;
})Quick Check
Test your understanding of React Native Mobile Development concepts from this lesson.
Lesson Recap
In this lesson you learned: createAsyncThunk wraps async operations and dispatches pending/fulfilled/rejected lifecycle actions automatically, extraReducers with builder.addCase handles each lifecycle to update loading and error state, and rejectWithValue lets you pass custom error data to the rejected handler. Next up we explore Zustand, a lightweight alternative to Redux.
Frequently asked questions
Is the “Async Thunks with createAsyncThunk” lesson free?
Yes — the full text of “Async Thunks with createAsyncThunk” is free to read here on the web, and the React Native Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the React Native Academy course, upgrade to CoddyKit PRO.
What will I learn in “Async Thunks with createAsyncThunk”?
Fetch data from an API inside a createAsyncThunk, handle the pending/fulfilled/rejected lifecycle in the slice's extraReducers, and display async status in the UI. You practise React Native Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start React Native Academy?
No prior experience is required. React Native Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Async Thunks with createAsyncThunk” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this React Native Academy lesson?
Yes. Every React Native Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Setting Up the Redux Store and Provider
- Creating Slices with createSlice
- Reading State with useSelector
- Async Thunks with createAsyncThunk