feat: Add isStore.

[stephenh]

Related Issues or Discussions

Related to my useStore prototypes (https://github.com/pmndrs/valtio/discussions/662)

Summary

When working generically with a store, and wanting to handle it recursively, it's useful to ask "is this nested value itself a store?".

Currently this is not necessary for Valtio & proxy-compare, b/c createSnapshot pushes "this is special"-ness into proxy-compare's markToTrack, but 3rd party libraries/hooks like useStore don't have that blessed push-based mechanism, so need a pull-/probed-based mechanism to detect store-ness/special-ness.

Very open to alternative approaches/impls that accomplish the "is this a store?" goal.

Check List

• [x] yarn run prettier for formatting code and docs

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[dai-shi]

isStore should be implemented on your end. Something like this:

const isStore = (x) => getVersion(x) !== undefined;

There might be room for improvement in docs.

I think I did it in some of my valtio third-party libraries.

Closing.

[dai-shi]

There might be room for improvement in docs.

Yeah, we should add this isStore recipe in: https://github.com/pmndrs/valtio/blob/main/docs/api/hacks/getVersion.mdx

Another impl:

const isStore = (x) => typeof getVersion(x) !== 'number'`;

BTW, I prefer isProxy to isStore.

[stephenh]

Ah darn it, I thought proxyStateMap was per proxyFunction but you're right it's global.

That makes sense! I forgot about getVersion.

Cool, I'll do that.

BTW, I prefer isProxy to isStore.

Yeah, my only nudge is that once we have ~2-3 types of proxies floating around, it can be hard to keep track of "which proxy is this again now?". :-)

But that's fine.

[stephenh]

Yeah, we should add this isStore recipe in:

Wdyt about adding isProxy but based on your impl, i.e. a helper method that just calls getVersion?

Just thinking it's a more ergonomic/more discoverable to users than having to find it as a suggested recipe in the getVersion docs and then implement their own.

[dai-shi]

It is only for library authors. I'd prefer hiding it in the getVersion docs.

[stephenh]

Sounds good. Fwiw just in terms of push-vs-pull, it might be neat if instead of markToTrack-ing every snapshot, Valtio just did like:

markToTrackFunction((obj) => isSnapshot(obj);

Which would let proxy-compare ask "should I proxy this object?" by just calling the function.

In theory it'd cut down on the overhead of pushing every snapshot into the mark to track set. :shrug:

Not a big deal, just mentioning as a potential micro-optimization.

[dai-shi]

Yeah, that would be another way. For now, I avoided it because it's not predictable in terms of performance. People can register a heavy function, and multiple functions (which requires to iterate those functions). But, let me keep that in mind for the future version of proxy-compare, which I want to simplify further (your suggestion of not supporting frozen object might be in.)

[stephenh]

People can register a heavy function

Good point!