Expo Go client and Metro bundler: Propagation of developer‑defined fetch timeouts

Answer

No. Expo Go and the Expo managed workflow do not honor a developer-specified timeout init option on fetch. The standard Web Fetch API has no timeout member. Passing fetch(url, { timeout: 5000 }) is non-standard and is silently ignored by React Native and Expo runtimes. It is not propagated to the native HTTP stack.

A timeout you define yourself is honored only when you implement it with the standard AbortController signal.

Confirmed Facts

• React Native's fetch implementation maps AbortController.signal to the native layer.
• Expo Go forwards abort signals to the native HTTP stack (OkHttp on Android and NSURLSession on iOS).
• The OTA update mechanism uses its own hard-coded timeouts which are separate from app-level fetch calls and not adjustable.

Likely Explanation

The Expo managed workflow does not expose a global fetch configuration. Effective timeout limits are determined by the underlying native stacks and OS conditions, which vary across SDK versions and platforms. Metro bundler only handles JavaScript bundling and does not affect runtime networking timeouts.

Steps to implement custom timeouts

To enforce a custom timeout in Expo Go, you must use the AbortController API combined with setTimeout:

const controller = new AbortController();
const timeout = setTimeout(() => controller.abort(), 5000);

try {
  const response = await fetch('https://api.example.com/data', { 
    signal: controller.signal 
  });
  const data = await response.json();n} catch (error) {
  if (error.name === 'AbortError') {
    console.log('Fetch timed out');
  } else {
    console.log('Network error', error);
  }
} finally {
  clearTimeout(timeout);
}

Note: Timeout-related errors from AbortController are distinct from generic network errors, but error messages can be similar. Always inspect the error.name to distinguish between an explicit abort and a transport failure.