reactive initialValue on createResource

is it possible to make initialValue react based on a signal? I have this:

  const [namespaces] = createResource(contexts, fetchNamespaces, {
    initialValue: getCachedNamespaces(contexts()),
  });

  const [namespaces] = createResource(contexts, fetchNamespaces, {
    initialValue: getCachedNamespaces(contexts()),
  });

Whenever the list of contexts change, it'll refetch the namespaces for that contexts. But the initialValue does not as it's evaluated once on render.

I want to build sort of a cache, so whenever the context changes, the list of namespaces will be whatever is cached (localstorage) and then it'll refresh shortly after.

goenningOP•12/7/22, 8:24 PM

this works, but I suspect it might have some race conditions here in case the mutate happens after fetch:

Alex Lohr•12/7/22, 8:32 PM

You can simply not run the effect if namespaces() is not undefined.

Alex Lohr•12/7/22, 8:33 PM

Don't forget to untrack it inside the effect: if (untrack(namespaces) !== undefined) { ... }

Alex Lohr•12/7/22, 8:46 PM

Ah, yes. Well, then you'll need an extra variable that is set inside the fetcher.

Alex Lohr•12/7/22, 8:46 PM

Or you return the last value of the context and compare with that.

goenningOP•12/7/22, 8:59 PM

So basically there’s no way to do it without the effect?

goenningOP•12/7/22, 8:59 PM

Just with the createResource?

Alex Lohr•12/7/22, 9:05 PM

Well, you could also derive the resource in a memo instead and use that:

Alex Lohr•12/7/22, 9:06 PM

Alex Lohr•12/7/22, 9:07 PM

then you don't have to mutate the resource and will always get the newest initialValue (that only gets updated when either serverNamespaces or contexts() changes).