focusThrottleInterval is not honoured for the first refresh on focus after mount

[mgoodfellow]

Bug report

Description / Observed Behavior

It seems that sometimes focusThrottleInterval is not honoured

Expected Behavior

I expected it to be honoured

Repro Steps / Code Example

https://github.com/mgoodfellow/swr_revalidate_test

Additional Context

SWR version 2.2.4

Add any other context about the problem here

Run repo with npm run dev

Page loads, cat fact shown.

Click away from window (lose focus)

Wait ~ 10 seconds, click back to window:

If we review this waterfall, we have filtered requests by "cat" so we see the requests for this URL.

We can see the request on the page load, then we see another request ~10s. Surely the focusThrottleInterval should have inhibited this 2nd request from occuring?

[mgoodfellow]

Some additional info: https://github.com/mgoodfellow/swr_revalidate_test/blob/master/swr-revalidate-test/src/pages/index.tsx#L15

It seems this value is honoured for subsequent requests, but the initial focusThrottleInterval after a page load is the default of 5s

[mgoodfellow]

Right, I see the issue:

swr/core/src/use-swr.ts

Line 594 in 1d81109

nextFocusRevalidatedAt = now + getConfig().focusThrottleInterval

The nextFocusRevalidatedAt is only calculated after the initial focus revalidation. So we end up with this issue where the first throttle interval is always ignored.

This effect is then repeated on a remount (such as due to a page change).

I guess ideally we need to calculate the next possible revalidation window due to focus, when it initially mounts.

swr/core/src/use-swr.ts

Line 579 in 1d81109

let nextFocusRevalidatedAt = 0

[mgoodfellow]

So updating my example from the initial repo: mgoodfellow/swr_revalidate_test#1

This uses the built libraries from the PR I opened above, and the behaviour is now as expected:

That initial refresh does not occur, and then the refresh on focus after 60s is allowed