When proxyShallow should be used?

[user753]

If I understand correctly it's just a slightly better version of shallowEqual but with the cost of proxy usage. With consideration of the proxy cost can I assume that it always works faster than shallowEqual? Why would I want to use proxyShalloow instead of proxyEqual?

[theKashey]

This is not only "when" question, but also "why". You might find some answers in my article How I wrote the world’s fastest memoization library, and in the series of articles and "usage-tracking" packages @dai-shi have created.

In short - proxyEqual is not shallowEqual. Even if they have similar signatures and doing almost the same job - they are different. proxyEqual requires one more argument, which contains all keys you are going to compare, and that list is generated by a factual usage, ie usage tracking.

But anyway there are 3 function to use - proxyEqual, proxyShallow, proxyShallowEqual, and dont forget about proxyState. And what is the difference.

• proxyEqual - the first comparison functions. Given state a, b and usage c - find all "end" values in c and perform the comparison. That is "end values" - in short that's a leafs. Having used keys as a, a.b, a.b.c, a.b.d it would return only a.b.c and a.b.d, and thus values of a and a.b would be ignored.
• proxyShallow - this is comparison optimisation function. Let's imagine you have a big state, with big, or deep tracked usage. proxyEqual would compare the "end" values, but what if state is not changed at all? proxyShallow is comparing everything except end values. It uses trie structure to find all keys with deeper reads inside, and thus you could make a faster comparison. And I am going to delete this function.
• proxyShallowEqual is the best of two worlds, and I encourage you to use it. It performs shallow and "end" comparison simultaneously, making the whole process much faster.
• there is also proxyCompare, which is low level comparison, and from some point of view is shallowEqual, but there are nuances.

And proxyState is providing the right memoization orchestration to make it even faster.

And look like it's time to update documentation :)

[user753]

And look like it's time to update documentation :)

It would be great. d.ts file doesn't even have proxyShallowEqual. Also, there is a typo in package.json "types": "proxyqual.d.ts",