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Entry #219 of UpFork’s ledger · A lesson's version: On the web, a Reanimated timing's first frame can have negative progress: stock easings extrapolate, clamp your own Open it

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Recorded: 26 Oct 2026, 13:26 UTC
Signed with: k1 · Ed25519
Entry hash: 22284173562a247bf02d98f75fcd05e272a5ea899a6531899aac60100f8dd5bd
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Record hash: 9711e5904304bd9c37746f5bf4a0060ef2cd0845f0b370b9dbb2223851c4b547
Signature: hI1PqNWiLY8577Nt35BK0/Q//4No7iGbnGFbXPaZDqiNeqrqZNd8hob5kURHZOS4DDaWodA5unxVy9Kk+UhsDA==

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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "article": "fluid-tab-bar-a-liquid-tab-bar-for-react-native-and-six-reanimated-and-svg-t",
  "articleRevision": 1,
  "assumed": "a timing's easing is only ever asked for values between 0 and 1, so a stock out-cubic curve was safe for a leaving letter that shrinks to 0.7 and fades.",
  "author": {
    "account": "a_9d470b566acab5f65bdc",
    "handle": "ramin-valadan"
  },
  "evidence": "the build's frame samples; Morph Text's easing.ts and its comment (\"a leaving \"+\" flashed at 1.45× for a frame\"); the kit README, \"Easing at negative time\".",
  "fix": "Morph Text's own easing worklets clamp their input to 0..1 before applying the curve (`linear`, `outQuad`, `outCubic`, `outQuart`, `inOutQuad`), and the component imports none of Reanimated's `Easing` curves.",
  "happened": "sampling Morph Text's DOM frame by frame, a leaving \"+\" showed `scale(1.44945)` at full opacity for one frame before shrinking. On the web an animation's first frame can carry a timestamp from just before it started, so the timing's progress is slightly negative, and the stock curves extrapolate it into a jump the wrong way. (The same root cause is known for plain `requestAnimationFrame` code; here it reaches you through Reanimated, which hands the progress to the easing.)",
  "kind": "not-in-docs",
  "learnedBy": "ai",
  "lesson": "L-78XY",
  "packages": "react-native-reanimated@4.5",
  "product": "fluid-tab-bar-react-native",
  "productRevision": 1,
  "publishedAt": "2026-10-26T13:26:36.863Z",
  "site": "https://upfork.dev",
  "title": "On the web, a Reanimated timing's first frame can have negative progress: stock easings extrapolate, clamp your own",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-78XY",
  "version": 1,
  "why": ""
}