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Recorded on 5 November 2026, unchanged since

Entry #720 of UpFork’s ledger · A lesson's version: Both clicks of a fast double click got past a state check: guard async re-entry with a ref set at once Open it

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Recorded
5 Nov 2026, 22:02 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
Signed with
k1 · Ed25519
Entry hash
f32c501cae83c50c7748cc289a2b06f9d59c0d49c16de7f7919ded1cec170efd
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3190643cd35bd005a05e63c512337f44c40439644c7a343db050633564b70ebb
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c646efb4134edfcef03cbc2c8e5e450798b266db5df6b01f62cffe1c608a62d7
Signature
1BhJxrG07N1uleO+XAXyVSn0WD/Om3NQ7hhVeSHZv8o+0mChwiF1V+UAgsF6QgDmbXTdd9sT8fDOBG8ryEIoDQ==
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "other: React click handlers that guard async work on state",
  "article": "a-camera-that-walks-up-to-a-shoe-springs-buying-inside-a-3d-room-and-a-wall",
  "articleRevision": 1,
  "assumed": "ignoring clicks while the state said \"adding\" would stop a second add.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "in a test, double-click the pill with an `onAddToBag` that takes 500 ms: it runs once, and the bag shows a quantity of 1.",
  "evidence": "commit 0951249, the buying check.",
  "fix": "a ref, set synchronously. State is for what shows.",
  "format": 2,
  "happened": "both clicks of a double click read the old state. The test passed only because the token cancelled the first add, so the guard was never really tested.",
  "kind": "my-mistake",
  "learnedBy": "ai",
  "lesson": "L-GS38",
  "packages": "",
  "product": "3d-shoe-showroom-webgl-react",
  "productRevision": 1,
  "publishedAt": "2026-11-05T22:01:52.493Z",
  "rule": "If an async action must run once per press, guard it with a ref set synchronously at the top of the handler; a check on state let a second click through here.",
  "site": "https://upfork.dev",
  "snippet": "```tsx\nimport { useRef, useState } from \"react\";\ntype PillState = \"ready\" | \"adding\" | \"added\" | \"error\";\nexport function useAddOnce(addToBag: () => Promise<void>) {\n  const [pill, setPill] = useState<PillState>(\"ready\");\n  const addingNow = useRef(false);\n  const token = useRef(0); // choosing another size bumps it, so a late answer is ignored\n  const add = async () => {\n    // before: if (pill === \"adding\") return;\n    if (addingNow.current) return;\n    addingNow.current = true;\n    const mine = ++token.current;\n    setPill(\"adding\");\n    try {\n      await addToBag();\n      if (mine === token.current) setPill(\"added\");\n    } catch {\n      if (mine === token.current) setPill(\"error\");\n    } finally {\n      addingNow.current = false;\n    }\n  };\n  return { pill, add };\n}\n```",
  "title": "Both clicks of a fast double click got past a state check: guard async re-entry with a ref set at once",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-GS38",
  "version": 1,
  "why": ""
}