Best way to handle Fetch errors such as Failed to fetch, NetworkError when attempting to fetch resource, etc.

[thojanssens]

We have these errors happening only occasionally and I'm not able to reproduce these errors.

1. Is it possible to retry only when errors are network errors: https://github.com/sindresorhus/is-network-error/blob/main/index.js ?

2. Does anyone know what causes these errors? Is it normal to explicitly catch and handle these specific errors or is it more likely a problem on my app or server? The server is just a Hetzner VPS with very basic configuration, I can't imagine it being that with the popularity that Hetzner has; as to the app, it only happens very occasionally, the same request will succeed after any subsequent attempt.

[sindresorhus]

1. You could use a hook:

import ky from 'ky';

const response = await ky('https://example.com', {
	hooks: {
		beforeRetry: [
			async ({error}) => {
				if (!isNetworkError(error)) {
					throw error;
				}
			}
		]
	},
	retry: {
		limit: 2, // Number of retry attempts
		methods: ['get'], // Methods to retry
		statusCodes: [0] // Include network errors (status code 0)
	}
});

However, I think it would be useful if Ky had a retry.shouldRetry function. Then it could simply be:

import ky from 'ky';

const response = await ky('https://example.com', {
	retry: {
		shouldRetry: ({error}) => isNetworkError(error)
	}
});

2. Hard to know for sure. The occasional network errors like 'Failed to fetch' can have various causes, including transient network issues. It's common to handle such errors in your app. The fact that the same request often succeeds on subsequent attempts suggests external factors may be at play, and the basic server configuration may not be the main issue.