expo/expo-data-fetching
Framework (OSS). Use when implementing or debugging ANY network request, API call, or data fetching. Covers fetch API, React Query, SWR, error handling, caching, offline support, and Expo Router data loaders (`useLoaderData`).
npx skills add https://github.com/expo/skills --skill expo-data-fetchingYou MUST use this skill for ANY networking work including API requests, data fetching, caching, or network debugging.
Consult these resources as needed:
references/
expo-router-loaders.md Route-level data loading with Expo Router loaders (web, SDK 55+)
offline-and-cancellation.md NetInfo network status, offline-first React Query, AbortController
Use this skill when:
useLoaderData, web SDK 55+)Simple GET request:
const fetchUser = async (userId: string) => {
const response = await fetch(`https://api.example.com/users/${userId}`);
if (!response.ok) {
throw new Error(`HTTP error! status: ${response.status}`);
}
return response.json();
};
POST request with body:
const createUser = async (userData: UserData) => {
const response = await fetch("https://api.example.com/users", {
method: "POST",
headers: {
"Content-Type": "application/json",
Authorization: `Bearer ${token}`,
},
body: JSON.stringify(userData),
});
if (!response.ok) {
const error = await response.json();
throw new Error(error.message);
}
return response.json();
};
Setup:
// app/_layout.tsx
import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
const queryClient = new QueryClient({
defaultOptions: {
queries: {
staleTime: 1000 * 60 * 5, // 5 minutes
retry: 2,
},
},
});
export default function RootLayout() {
return (
<QueryClientProvider client={queryClient}>
<Stack />
</QueryClientProvider>
);
}
Fetching data:
import { useQuery } from "@tanstack/react-query";
function UserProfile({ userId }: { userId: string }) {
const { data, isLoading, error, refetch } = useQuery({
queryKey: ["user", userId],
queryFn: () => fetchUser(userId),
});
if (isLoading) return <Loading />;
if (error) return <Error message={error.message} />;
return <Profile user={data} />;
}
Mutations:
import { useMutation, useQueryClient } from "@tanstack/react-query";
function CreateUserForm() {
const queryClient = useQueryClient();
const mutation = useMutation({
mutationFn: createUser,
onSuccess: () => {
// Invalidate and refetch
queryClient.invalidateQueries({ queryKey: ["users"] });
},
});
const handleSubmit = (data: UserData) => {
mutation.mutate(data);
};
return <Form onSubmit={handleSubmit} isLoading={mutation.isPending} />;
}
Comprehensive error handling:
class ApiError extends Error {
constructor(message: string, public status: number, public code?: string) {
super(message);
this.name = "ApiError";
}
}
const fetchWithErrorHandling = async (url: string, options?: RequestInit) => {
try {
const response = await fetch(url, options);
if (!response.ok) {
const error = await response.json().catch(() => ({}));
throw new ApiError(
error.message || "Request failed",
response.status,
error.code
);
}
return response.json();
} catch (error) {
if (error instanceof ApiError) {
throw error;
}
// Network error (no internet, timeout, etc.)
throw new ApiError("Network error", 0, "NETWORK_ERROR");
}
};
Retry logic:
const fetchWithRetry = async (
url: string,
options?: RequestInit,
retries = 3
) => {
for (let i = 0; i < retries; i++) {
try {
return await fetchWithErrorHandling(url, options);
} catch (error) {
if (i === retries - 1) throw error;
// Exponential backoff
await new Promise((r) => setTimeout(r, Math.pow(2, i) * 1000));
}
}
};
Token management:
import * as SecureStore from "expo-secure-store";
const TOKEN_KEY = "auth_token";
export const auth = {
getToken: () => SecureStore.getItemAsync(TOKEN_KEY),
setToken: (token: string) => SecureStore.setItemAsync(TOKEN_KEY, token),
removeToken: () => SecureStore.deleteItemAsync(TOKEN_KEY),
};
// Authenticated fetch wrapper
const authFetch = async (url: string, options: RequestInit = {}) => {
const token = await auth.getToken();
return fetch(url, {
...options,
headers: {
...options.headers,
Authorization: token ? `Bearer ${token}` : "",
},
});
};
Token refresh:
let isRefreshing = false;
let refreshPromise: Promise<string> | null = null;
const getValidToken = async (): Promise<string> => {
const token = await auth.getToken();
if (!token || isTokenExpired(token)) {
if (!isRefreshing) {
isRefreshing = true;
refreshPromise = refreshToken().finally(() => {
isRefreshing = false;
refreshPromise = null;
});
}
return refreshPromise!;
}
return token;
};
Network-status detection with NetInfo and offline-first React Query setup: see ./references/offline-and-cancellation.md.
Using environment variables for API configuration:
Expo supports environment variables with the EXPO_PUBLIC_ prefix. These are inlined at build time and available in your JavaScript code.
// .env
EXPO_PUBLIC_API_URL=https://api.example.com
EXPO_PUBLIC_API_VERSION=v1
// Usage in code
const API_URL = process.env.EXPO_PUBLIC_API_URL;
const fetchUsers = async () => {
const response = await fetch(`${API_URL}/users`);
return response.json();
};
Environment-specific configuration:
// .env.development
EXPO_PUBLIC_API_URL=http://localhost:3000
// .env.production
EXPO_PUBLIC_API_URL=https://api.production.com
Creating an API client with environment config:
// api/client.ts
const BASE_URL = process.env.EXPO_PUBLIC_API_URL;
if (!BASE_URL) {
throw new Error("EXPO_PUBLIC_API_URL is not defined");
}
export const apiClient = {
get: async <T,>(path: string): Promise<T> => {
const response = await fetch(`${BASE_URL}${path}`);
if (!response.ok) throw new Error(`HTTP ${response.status}`);
return response.json();
},
post: async <T,>(path: string, body: unknown): Promise<T> => {
const response = await fetch(`${BASE_URL}${path}`, {
method: "POST",
headers: { "Content-Type": "application/json" },
body: JSON.stringify(body),
});
if (!response.ok) throw new Error(`HTTP ${response.status}`);
return response.json();
},
};
Important notes:
EXPO_PUBLIC_ are exposed to the client bundleEXPO_PUBLIC_ variables—they're visible in the built app.env filesEXPO_PUBLIC_ prefixTypeScript support:
// types/env.d.ts
declare global {
namespace NodeJS {
interface ProcessEnv {
EXPO_PUBLIC_API_URL: string;
EXPO_PUBLIC_API_VERSION?: string;
}
}
}
export {};
AbortController on unmount (React Query cancels automatically): see ./references/offline-and-cancellation.md.
User asks about networking
|-- Route-level data loading (web, SDK 55+)?
| \-- Expo Router loaders — see references/expo-router-loaders.md
|
|-- Basic fetch?
| \-- Use fetch API with error handling
|
|-- Need caching/state management?
| |-- Complex app -> React Query (TanStack Query)
| \-- Simpler needs -> SWR or custom hooks
|
|-- Authentication?
| |-- Token storage -> expo-secure-store
| \-- Token refresh -> Implement refresh flow
|
|-- Error handling?
| |-- Network errors -> Check connectivity first
| |-- HTTP errors -> Parse response, throw typed errors
| \-- Retries -> Exponential backoff
|
|-- Offline support?
| |-- Check status -> NetInfo
| \-- Queue requests -> React Query persistence
|
|-- Environment/API config?
| |-- Client-side URLs -> EXPO_PUBLIC_ prefix in .env
| |-- Server secrets -> Non-prefixed env vars (API routes only)
| \-- Multiple environments -> .env.development, .env.production
|
\-- Performance?
|-- Caching -> React Query with staleTime
|-- Deduplication -> React Query handles this
\-- Cancellation -> AbortController or React Query
Wrong: No error handling
const data = await fetch(url).then((r) => r.json());
Right: Check response status
const response = await fetch(url);
if (!response.ok) throw new Error(`HTTP ${response.status}`);
const data = await response.json();
Wrong: Storing tokens in AsyncStorage
await AsyncStorage.setItem("token", token); // Not secure!
Right: Use SecureStore for sensitive data
await SecureStore.setItemAsync("token", token);
User: "How do I make API calls in React Native?"
-> Use fetch, wrap with error handling
User: "Should I use React Query or SWR?"
-> React Query for complex apps, SWR for simpler needs
User: "My app needs to work offline"
-> Use NetInfo for status, React Query persistence for caching
User: "How do I handle authentication tokens?"
-> Store in expo-secure-store, implement refresh flow
User: "API calls are slow"
-> Check caching strategy, use React Query staleTime
User: "How do I configure different API URLs for dev and prod?"
-> Use EXPO_PUBLIC_ env vars with .env.development and .env.production files
User: "Where should I put my API key?"
-> Client-safe keys: EXPO_PUBLIC_ in .env. Secret keys: non-prefixed env vars in API routes only
User: "How do I load data for a page in Expo Router?"
-> See references/expo-router-loaders.md for route-level loaders (web, SDK 55+). For native, use React Query or fetch.
If you encounter errors, misleading or outdated information in this skill, report it so Expo can improve:
npx --yes submit-expo-feedback@latest --category skills --subject "expo-data-fetching" "<actionable feedback>"
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