JavaScript answer
TypeError: Failed to fetch
The browser throws TypeError: Failed to fetch when fetch fails before JavaScript receives a Response object.
Common causes
What usually causes this JavaScript error.
Start with the runtime condition that produced the error, then narrow by route, release, browser, and user action.
The API does not allow the browser origin through CORS.
The user is offline, a proxy blocked the request, or DNS/TLS failed.
The page is HTTPS but the request targets an HTTP URL.
The request URL, method, headers, credentials, or preflight response is invalid.
Reproduce
How to reproduce the failure.
Block the endpoint or call an API without expected CORS headers.
try {
await fetch("https://api.example.test/private", { credentials: "include" });
} catch (error) {
console.error("Request never produced a readable response", error);
}Fix
How to fix it.
Apply the smallest code change that makes the missing, nullable, blocked, or timing-sensitive value explicit.
Separate network rejection from HTTP errors
Use try/catch for transport failures, then check response.ok after fetch resolves.
let response: Response;
try {
response = await fetch("/api/profile");
} catch {
return { ok: false, reason: "network" };
}
if (!response.ok) return { ok: false, reason: response.status };Record request context
Capture route, endpoint, release, and retry count around failed browser requests.
addBreadcrumb({
category: "fetch",
message: "GET /api/profile failed",
data: { route: location.pathname, retryCount },
});Production monitoring
How to prevent and monitor it in production.
Once the local fix is clear, production monitoring should tell you whether the same failure is isolated, user-impacting, or tied to a release.
Group failures by endpoint, browser, route, release, and online state.
Attach fetch breadcrumbs and replay so responders can see the triggering user action.
Alert on deploy-linked spikes instead of every isolated offline client.