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Marc-André Bombeck
1a101505c4
The 10% sampling decision in WebVitalsReporter (v1.4.33 F19) was
computed inline in useMemo(), which the react-hooks/purity lint rule
rejects: Math.random() is impure and the render body must be
idempotent. The original useMemo() happened to be stable in practice
(empty dep array) but the rule fires regardless because the
expression inside the memo factory is impure.
Move the draw into useEffect(() => {}, []) and stash the result in a
useRef so every reportWebVitals callback in the same navigation reads
the same decision. SSR seeds the ref to null, so a pre-hydration
beacon (which would have no rate-limit relief value) is dropped; the
first post-hydration callback finds the ref populated and decides
whether to POST. Bundle and runtime cost unchanged — same one draw
per mount, same all-or-none per page-load. ESLint clean.