alt Hacker NewsThe fact we got to a point of auto-memoization on every reactive function is crazy to me. How is that not prematurely optimizing? I already saw people doing useMemo on shit that shouldn't be getting called repeatedly with the same value. So maybe it is better to let a compiler decide, although I am curious how it knows.
EDIT: if its pure (not reactive to any other variable but other variables may react to it) they will auto memoize I guess to avoid their own reactivity engine doing a bunch of useless shit when no value was actually updated. Correct me here if I am wrong.
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It automemoizes objects that would otherwise be recreated on each render, which would then cause rerenders down the tree. By memoizing these objects, they reduce the amount of rerendering done without actually changing the semantics of the code you write (unless you wrote code that only works because of frequent unnecessary rendering).
Just to clarify: despite its name, React has no reactivity engine at all and re-renders unconditionally on any state changes or parent re-renders.
You have to opt-in to prop-diffing conditional re-renders (which I wouldn't call a "reactivity engine" either) per component, via React.memo.
And then you also have to opt-in to prop memoization for non-primitives for the prop-diffing not to be useless.
These re-renders might not result in any actual DOM changes since there is an additional vDOM diffing step from the resulting render (which, again, I wouldn't call a "reactivity engine").