How it is implemented

A source-to-source pass runs before JSX compilation (deriveLocals). const double = count() * 2 becomes const double = _$derived(() => (count() * 2)), every read of double in JSX or a closure becomes double.value, and a call double() is left as written because the derived value is callable. derived is a documented export of @shadow-js/web (and of @shadow-js/web/server): see derived. It wraps a useMemo, which is why the caching and dependency tracking behave exactly like a memo.

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