What is a Fetch Network Error?

fetch() rejects with a TypeError when a network-level failure prevents the request from completing. This is different from an HTTP error status (4xx/5xx): a network error means no response was received at all. Common causes include the server being down, DNS resolution failure, or a CORS preflight rejection.

Why it happens

• •The server is not running or the URL is unreachable.
• •A CORS preflight (OPTIONS) request was rejected before the main request.
• •The browser is offline or the network connection dropped.
• •An invalid URL scheme or hostname causes DNS resolution to fail.

Examples

const data = await fetch("https://localhost:9999/api");
const json = await data.json();

TypeError: Failed to fetch

try {
  const res = await fetch("https://api.example.com/data");
  if (!res.ok) throw new Error(`HTTP ${res.status}`);
  const json = await res.json();
} catch (err) {
  if (err instanceof TypeError) {
    console.error("Network error:", err.message);
  } else {
    console.error("API error:", err.message);
  }
}

Related errors

• CORS Error
• UnhandledPromiseRejection
• ECONNRESET