pyfagorass Expo Networking
You MUST use this skill for ANY networking work including API requests, data fetching, caching, or network debugging.
References
Consult these resources as needed:
references/
expo-router-loaders.md Route-level data loading with Expo Router loaders (web, SDK 55+)
When to Use
Use this skill when:
- Implementing API requests
- Setting up data fetching (React Query, SWR)
- Using Expo Router data loaders (
useLoaderData, web SDK 55+) - Debugging network failures
- Implementing caching strategies
- Handling offline scenarios
- Authentication/token management
- Configuring API URLs and environment variables
Preferences
- Avoid axios, prefer expo/fetch
Common Issues & Solutions
1. Basic Fetch Usage
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();
};
2. React Query (TanStack Query)
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 isLoading={mutation.isPending} />;
}
3. Error Handling
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));
}
}
};
4. Authentication
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 ${token}` : "",
},
});
};
Token refresh:
let isRefreshing = false;
let refreshPromise: Promise<string> | null = null;
const getValidToken = async (): Promise<string> => {
const token = await auth.getToken();
if (!token || isTokenExpired(token)) {
if (!isRefreshing) {
isRefreshing = true;
refreshPromise = refreshToken().finally(() => {
isRefreshing = false;
refreshPromise = null;
});
}
return refreshPromise!;
}
return token;
};
5. Offline Support
Check network status:
import NetInfo from "@react-native-community/netinfo";
// Hook for network status
function useNetworkStatus() {
const [isOnline, setIsOnline] = useState(true);
useEffect(() => {
return NetInfo.addEventListener((state) => {
setIsOnline(state.isConnected ?? true);
});
}, []);
return isOnline;
}
Offline-first with React Query:
import { onlineManager } from "@tanstack/react-query";
import NetInfo from "@react-native-community/netinfo";
// Sync React Query with network status
onlineManager.setEventListener((setOnline) => {
return NetInfo.addEventListener((state) => {
setOnline(state.isConnected ?? true);
});
});
// Queries will pause when offline and resume when online
6. Environment Variables
Using environment variables for API configuration:
Expo supports environment variables with the EXPO_PUBLIC_ prefix. These are inlined at build time and available in your JavaScript code.
// .env
EXPO_PUBLIC_API_URL=https://api.example.com
EXPO_PUBLIC_API_VERSION=v1
// Usage in code
const API_URL = process.env.EXPO_PUBLIC_API_URL;
const fetchUsers = async () => {
const response = await fetch(`${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:
- Only variables prefixed with
EXPO_PUBLIC_are exposed to the client bundle - Never put secrets (API keys with write access, database passwords) in
EXPO_PUBLIC_variables—they're visible in the built app - Environment variables are inlined at build time, not runtime
- Restart the dev server after changing
.envfiles - For server-side secrets in API routes, use variables without the
EXPO_PUBLIC_prefix
TypeScript support:
// types/env.d.ts
declare global {
namespace NodeJS {
interface ProcessEnv {
EXPO_PUBLIC_API_URL: string;
EXPO_PUBLIC_API_VERSION?: string;
}
}
}
export {};
7. Request Cancellation
Cancel on unmount:
useEffect(() => {
const controller = new AbortController();
fetch(url, { signal: controller.signal })
.then((response) => response.json())
.then(setData)
.catch((error) => {
if (error.name !== "AbortError") {
setError(error);
}
});
return () => controller.abort();
}, [url]);
With React Query (automatic):
// React Query automatically cancels requests when queries are invalidated
// or components unmount
Decision Tree
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
Common Mistakes
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);
Example Invocations
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 EXPOPUBLIC env vars with .env.development and .env.production files
User: "Where should I put my API key?" -> Client-safe keys: EXPOPUBLIC 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.