Fetch API

fetch() is the global function React Native provides for HTTP requests, with the same promise-based API as in browsers. Underneath, it is not a browser: requests are handed to the platform’s native networking stack on iOS and Android, which explains most of the ways it behaves differently from the web.

const controller = new AbortController();
const timer = setTimeout(() => controller.abort(), 10_000);

const res = await fetch('https://api.example.com/orders', { signal: controller.signal });
clearTimeout(timer);
if (!res.ok) throw new Error(`HTTP ${res.status}`);
const orders = await res.json();

Differences that matter on mobile:

• No CORS on native. CORS is a browser rule, so native requests ignore it. The same code may fail on web, which is a server configuration problem, not a React Native one.
• Plain HTTP is blocked by default. iOS App Transport Security and Android (since Android 9) refuse cleartext http:// traffic unless you add an exception. A local API that works in the browser often fails on a device for this reason.
• localhost is the device, not your computer. From the Android emulator, your machine is 10.0.2.2; from a physical phone, use your machine’s LAN address.
• Streaming is limited. React Native’s built-in fetch does not expose response bodies as streams. Expo provides expo/fetch with streaming support for cases such as reading an LLM response token by token.

The mistakes that show up in production are about the network, not the API. fetch only rejects on network failure; a 401 or 500 resolves normally, so always check res.ok. And there is no default timeout, so on a weak mobile connection a request can hang far longer than any user will wait; abort it yourself as above.

For caching, retries and refetching, wrap fetch with TanStack Query rather than calling it directly from effects. For connections that must stay open, use a WebSocket. See networking.