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Recorded
6 Nov 2026, 06:30 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
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k1 · Ed25519
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "other: installed Chrome driven over its DevTools debug port (the occlusion flag is for Windows)",
  "article": "a-3d-shoe-showroom-in-raw-webgl2-line-lights-clear-acrylic-soft-shadows-and",
  "articleRevision": 2,
  "assumed": "a back tab, a minimised window or a page in a second context would be hidden.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "the first read prints `hidden` and the second `visible`.",
  "evidence": "commit badceaf, `hidden.mjs`.",
  "fix": "raw DevTools over the debug port, with native occlusion switched off.",
  "format": 2,
  "happened": "all of them stayed `visible`: a back tab in headless Chrome, a headed window in a new context, a minimised window, focus emulation switched off through CDP, and the backgrounding flags removed. Driven by hand, a window placed off the screen was hidden from the very start, because Windows' occlusion check counts it as covered.",
  "kind": "tools",
  "learnedBy": "ai",
  "lesson": "L-AYBF",
  "packages": "",
  "product": "3d-shoe-showroom-webgl-react",
  "productRevision": 2,
  "publishedAt": "2026-11-06T06:30:29.854Z",
  "rule": "If a test needs `document.visibilityState` to be `hidden` and Playwright's pages stay `visible`, start installed Chrome with a debug port and open a second tab over the first via `/json/new`.",
  "site": "https://upfork.dev",
  "snippet": "```js\n// Node 22 or later: global fetch and WebSocket.\nimport { spawn } from \"node:child_process\";\nconst base = \"http://127.0.0.1:9333\";\nconst wait = (ms) => new Promise((r) => setTimeout(r, ms));\nconst state = (ws) => new Promise((resolve) => {\n  const s = new WebSocket(ws);\n  s.onopen = () => s.send(JSON.stringify({ id: 1, method: \"Runtime.evaluate\", params: { expression: \"document.visibilityState\" } }));\n  s.onmessage = (e) => { s.close(); resolve(JSON.parse(e.data).result.result.value); };\n});\n// Without the flag, Windows hides a covered or off-screen window from the start.\nconst chrome = spawn(\"C:/Program Files/Google/Chrome/Application/chrome.exe\", [\"--remote-debugging-port=9333\",\n  \"--user-data-dir=.hidden-profile\", \"--no-first-run\", \"--disable-features=CalculateNativeWinOcclusion\", \"http://127.0.0.1:6813/\"]);\ntry {\n  let pages;\n  for (let i = 0; i < 50 && !pages; i++) pages = await fetch(`${base}/json`).then((r) => r.json()).catch(() => wait(200));\n  const ours = pages.find((t) => t.type === \"page\");\n  const other = await (await fetch(`${base}/json/new?about:blank`, { method: \"PUT\" })).json();\n  await wait(500);\n  console.log(await state(ours.webSocketDebuggerUrl)); // hidden\n  await fetch(`${base}/json/activate/${ours.id}`);\n  await wait(500);\n  console.log(await state(ours.webSocketDebuggerUrl)); // visible\n  await fetch(`${base}/json/close/${other.id}`);\n} finally {\n  chrome.kill();\n}\n```",
  "title": "Playwright kept every page visible: drive installed Chrome over its debug port for a real hidden tab",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-AYBF",
  "version": 2,
  "why": ""
}