Reverts to initialData when key is reset to null

[GriffinSauce]

When passing initialData and using conditional fetching the data will reset to initialData when the condition is set to falsy instead of leaving it on the last-fetched data.

Example:

const { data } = useSWR(
  shouldFetch ? `/api/things` : null,
  apiFetch,
  {
    initialData: dataFromSSR
  },
);

1. Change shouldFetch to true -> will fetch fresh data
2. Change shouldFetch to false -> data reverts to initialData instead of staying "fresh"

---

I've created a workaround that displays the behaviour I expected:

// SWR hack: don't revalidate when closed but do pass latest data to initialData
const initialDataRef = useRef(dataFromSSR);
const { data } = useSWR(
  shouldFetch ? `/api/things` : null,
  apiFetch,
  {
    initialData: initialDataRef.current,
  },
);
useEffect(
  () => {
    initialDataRef.current = data;
  },
  [data],
);

1. Change shouldFetch to true -> will fetch fresh data
2. Change shouldFetch to false -> last fetched data will be returned

---

I appreciate that resetting data to null when no initialData is passed makes sense, so I'm not sure what the best solution is but the current behaviour is a bit whacky with this combo of settings.

[nandorojo]

Would something like this work? Not sure if initialData updates, so maybe this wouldn't work, just an idea.

const { data } = useSWR(
  shouldFetch ? `/api/things` : null,
  apiFetch,
  {
    initialData: shouldFetch ? dataFromSSR : null
  },
)