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Recorded on 14 November 2026, unchanged since

Entry #818 of UpFork’s ledger · A lesson's version: On the web, write a hot Reanimated transform to the element yourself: the style mapper converts every style each frame Open it

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Recorded
14 Nov 2026, 09:05 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
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k1 · Ed25519
Entry hash
2af91e078382cfcb0d5add1fb3f1e236da4a00d940cb6b6b6d944db6a883fcd6
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f8cdcece7cb3a3a9c050ac4fe9b2fe16087672575a8e4726dcac2529ee6b3133
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348d27bb586b06419622db21921afc1f13334c467f37e9a9fee3b063c6855dee
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/a3IfZn0sy7SPabCLhNIqT1MT1GqvhlEOFUSobl2duoY0eBE3nNi9ek+2cLWkqeyrqVsAGisJc+bXFGHBDjvCA==
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "react-native-reanimated@>=4.5 <5, react-native-web@>=0.21 <0.22",
  "article": "a-garment-rail-in-react-native-where-each-piece-turns-on-its-hook-perspectiv",
  "articleRevision": 1,
  "assumed": "Reanimated's animated styles were the cheapest way to move a view on the web too.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "profile a drag at 1× and 3× DPR before and after: the style mapper's share falls, and frame p95 drops (here drag 21 → 19.5 ms, arrow step 22 → 17.5–18 ms).",
  "evidence": "at 1× CPU and 3× DPR on a busy machine, drag p95 21 → 19.5 ms, flick 21 → 18–19.5, step 22 → 17.5–18, fling to the end 23.5 → 18.2–18.5 (commit a22aa93).",
  "fix": "the piece roots, tags and threads write their transform (and z and opacity) to their own element in a `useAnimatedReaction`, only when the string changed; the roots are plain Views on the web so the ref is the element; phones keep the mappers.",
  "format": 2,
  "happened": "after layers and settled values, the remaining script per frame was mostly Reanimated's web style mapper handing every animated style to React Native Web, which resolved and converted the whole style each time, for every piece root, tag and thread.",
  "kind": "not-in-docs",
  "learnedBy": "ai",
  "lesson": "L-GHTB",
  "packages": "react-native-reanimated@4.5.1, react-native-web@0.21.4",
  "product": "fashion-shop-product-carousel-react-native",
  "productRevision": 1,
  "publishedAt": "2026-11-14T09:04:42.943Z",
  "rule": "If a web profile shows Reanimated's style mapper converting many moving views' styles each frame, write their transform to the element in a useAnimatedReaction, only on change.",
  "site": "https://upfork.dev",
  "snippet": "```tsx\n// before: an animated style on every piece's root\nconst root = useAnimatedStyle(() => ({ transform: [{ translateX: f.x }, { translateY: f.y }, { rotate: `${psi}deg` }] }));\n// after (web only; WEB is a module constant, so the hooks' order never changes)\nif (WEB) {\n  useAnimatedReaction(\n    () => { const f = frames.value[i]; return `translate(${f.x}px, ${f.y}px) rotate(${psiV.value}deg)`; },\n    (v, was) => { if (v !== was && ref.current) (ref.current as unknown as HTMLElement).style.transform = v; },\n  );\n}\n// the root is a plain View on the web, so its ref is the DOM element\n```",
  "title": "On the web, write a hot Reanimated transform to the element yourself: the style mapper converts every style each frame",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-GHTB",
  "version": 1,
  "why": "on the web the worklets already run on the page's own thread, so the mapper buys nothing there but the conversion."
}