Add retry.delay option to control the time between retries

[rclarey]

Related to option (2) to #509

Changes

• add delay function to RetryOptions object
• add test for using delay

[rclarey]

@sindresorhus @szmarczak @sholladay Sorry, can you please take a look when you have a chance

[sindresorhus]

You need to document it in the readme too.

[TommySorensen]

FYI: @sindresorhus After the changes in this PR, then i'm seeing warnings in NextJS like this on all my endpoints.

 ⚠ fetch for https://myspeficisomeurl.com on /cart specified "cache: default" and "revalidate: 60", only one should be specified.

I'm using ky pretty much basic. But it seems like that KY internally is adding the cache to the fetcher with value of default.

const contentApi = ky.create({
  prefixUrl: `${process.env.CONTENT_API_URL}/api`,
  retry: 0,
});

contentApi
    .get(`getSomething/${someId}`, {
      next: { revalidate: 60 },
    })
    .json();

[rclarey]

@TommySorensen this is because Ky internally constructs a Request, and the browser will automatically set request.cache to "default" if it's not specified. So this is an issue with Next's warning rather than an issue with Ky.

I just checked and it seems this was fixed in Next.js in https://github.com/vercel/next.js/pull/58505, and released in https://github.com/vercel/next.js/releases/tag/v14.0.3

BTW if like me you're not using Next 14 yet, this is a workaround I've been using:

function fetchWith(override: RequestInit): typeof fetch {
  return (input, init) => {
    if (input instanceof Request) {
      return fetch(input.url, {
        // Copy all properties *except* for `cache` to prevent Next from warning that
        // we pass both `cache` and `revalidate`.
        // This happens because Ky internally constructs a `Request` object, so `cache`
        // will always be the set to `"default"` even when we don't explicitly set it.
        body: input.body,
        credentials: input.credentials,
        headers: input.headers,
        integrity: input.integrity,
        keepalive: input.keepalive,
        method: input.method,
        mode: input.mode,
        redirect: input.redirect,
        referrer: input.referrer,
        referrerPolicy: input.referrerPolicy,
        signal: input.signal,
        ...init,
        ...override,
      });
    }
    return fetch(input, { ...init, ...override });
  };
}

// then use it like
contentApi
  .get(`getSomething/${someId}`, {
    fetch: fetchWith({ next: { revalidate: 60 } }),
  })
  .json();