is-network-error/index.js

Check if a value is a Fetch network error

const objectToString = Object.prototype.toString;

const isError = value => objectToString.call(value) === '[object Error]';

const errorMessages = new Set([
	'network error', // Chrome
	'Failed to fetch', // Chrome
	'NetworkError when attempting to fetch resource.', // Firefox
	'The Internet connection appears to be offline.', // Safari 16
	'Network request failed', // `cross-fetch`
	'fetch failed', // Undici (Node.js)
	'terminated', // Undici (Node.js)
	' A network error occurred.', // Bun (WebKit)
]);

export default function isNetworkError(error) {
	const isValid = error
		&& isError(error)
		&& error.name === 'TypeError'
		&& typeof error.message === 'string';

	if (!isValid) {
		return false;
	}

	const {message, stack} = error;

	// Safari 17+ has generic message but no stack for network errors
	if (message === 'Load failed') {
		return stack === undefined
			// Sentry adds its own stack trace to the fetch error, so also check for that
			|| '__sentry_captured__' in error;
	}

	// Deno network errors start with specific text
	if (message.startsWith('error sending request for url')) {
		return true;
	}

	// Standard network error messages
	return errorMessages.has(message);
}