[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"verticals":3,"playground-long-animation-frames-api":44,"search-suggestions":58},[4,20,32],{"id":5,"slug":6,"name":7,"tagline":8,"description":9,"accentFrom":10,"accentTo":11,"icon":12,"defaultLocale":13,"locales":14,"features":16,"position":19},"019fe637-3d33-714b-b57f-23e163ffca0c","dev","Web Development","Read it. Run it. Prove it.","A post a day on modern web development — most with an editable playground and a quiz that explains every answer. Free, no account needed.","violet-500","cyan-400","◇","en",[13,15],"fa",{"courses":17,"paths":17,"articles":17,"exams":18,"flashcards":18,"packages":17,"community":17,"certificates":17,"teams":17,"commerce":17},true,false,0,{"id":21,"slug":22,"name":23,"tagline":24,"description":25,"accentFrom":26,"accentTo":10,"icon":27,"defaultLocale":13,"locales":28,"features":30,"position":31},"019fe637-3dc2-754c-8657-0f175bfee7c6","lang","Languages","Learn a language the way you learn a codebase.","Grammar explained the way good documentation explains an API — one idea at a time, each with a quiz.","amber-400","⌘",[13,15,29],"es",{"courses":18,"paths":18,"articles":17,"exams":18,"flashcards":17,"packages":18,"community":17,"certificates":17,"teams":18,"commerce":18},2,{"id":33,"slug":34,"name":35,"tagline":36,"description":37,"accentFrom":38,"accentTo":39,"icon":40,"defaultLocale":13,"locales":41,"features":42,"position":43},"7b3c16f2-931d-410e-802e-e1fa4edab7de","soft","Soft Skills","The half of the job nobody wrote documentation for.","Weekly, on the parts of working life that decide more than your code does — first weeks, meetings, interviews, promotions, and the people around you. Written from what actually happens, and recorded as a podcast you can listen to on the walk.","emerald-400","teal-300","◉",[13],{"courses":18,"paths":18,"articles":17,"exams":18,"flashcards":18,"packages":18,"community":17,"certificates":18,"teams":18,"commerce":18},3,{"slug":45,"title":46,"summary":47,"html":48,"css":49,"js":50,"config":51,"doc":53},"long-animation-frames-api","Long Animation Frames — interactive playground",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">🎮 What's actually inside your slow click handler?\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      This button updates a real, hidden grid of rows in your own browser — no simulation.\n      Pick how it writes to the DOM, then click it and watch a live \u003Ccode>PerformanceObserver\u003C\u002Fcode>\n      name exactly which part of the frame was JavaScript and which part was the browser\n      forced to recalculate layout mid-script.\n    \u003C\u002Fp>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> How the handler touches the DOM\u003C\u002Fdiv>\n      \u003Cdiv class=\"seg\" id=\"modeSeg\" role=\"group\" aria-label=\"write pattern\">\n        \u003Cbutton data-mode=\"interleaved\" aria-pressed=\"true\">Interleaved — read a size right after every write\u003C\u002Fbutton>\n        \u003Cbutton data-mode=\"batched\" aria-pressed=\"false\">Batched — write everything, then read once\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cp class=\"hint\" id=\"modeHint\">Each row's height is set, then its height is immediately read back — once per row. That read forces the browser to recompute layout before it can answer.\u003C\u002Fp>\n\n      \u003Cdiv class=\"field\" style=\"margin-top:14px\">\n        \u003Cdiv class=\"ctl-label\">\n          \u003Cspan>Rows the handler updates\u003C\u002Fspan>\n          \u003Cspan class=\"mono\" id=\"countLabel\">800\u003C\u002Fspan>\n        \u003C\u002Fdiv>\n        \u003Cinput type=\"range\" id=\"count\" min=\"50\" max=\"2500\" step=\"50\" value=\"800\" \u002F>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"presets\" style=\"margin-top:12px\">\n        \u003Cbutton class=\"btn sm\" data-count=\"100\">100 rows (barely noticeable)\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-count=\"800\">800 rows (typical filtered table)\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-count=\"2500\">2500 rows (the ticket that got filed)\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"btn-row\" style=\"margin-top:16px\">\n        \u003Cbutton class=\"btn primary\" id=\"runBtn\">🖱️ Click to filter\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> Result — what the frame actually did\u003C\u002Fdiv>\n      \u003Cdiv class=\"status\" id=\"statusRow\">\n        \u003Cspan class=\"dot info\" id=\"dot\">\u003C\u002Fspan>\n        \u003Cspan id=\"statusText\">Click the button above — this reads real timing from your browser's own performance APIs.\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"frame-bar\" id=\"frameBar\" aria-hidden=\"true\">\u003C\u002Fdiv>\n      \u003Cdiv class=\"legend\">\n        \u003Cspan>\u003Cspan class=\"swatch seg-script\">\u003C\u002Fspan> script execution\u003C\u002Fspan>\n        \u003Cspan>\u003Cspan class=\"swatch seg-layout\">\u003C\u002Fspan> forced style\u002Flayout\u003C\u002Fspan>\n        \u003Cspan>\u003Cspan class=\"swatch seg-idle\">\u003C\u002Fspan> idle \u002F not attributed\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"output\" id=\"breakdown\" style=\"margin-top:14px\">\u003C\u002Fdiv>\n      \u003Cp class=\"hint\" id=\"resultHint\">\n        \"Interleaved\" forces a layout recalculation on every single row. \"Batched\" forces at most one,\n        at the very end — same visual result, far less forced work.\n      \u003C\u002Fp>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">3\u003C\u002Fspan> The observer reading this\u003C\u002Fdiv>\n      \u003Cdiv class=\"code\" id=\"codeOut\">\u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n  \u003C\u002Fdiv>\n\n  \u003Cdiv class=\"rowstage\" id=\"stage\" aria-hidden=\"true\">\u003C\u002Fdiv>","\u002F*\n * Shared playground design system — daily-post\n * ============================================\n * Link it from any post's playground\u002Findex.html (no per-post boilerplate):\n *\n *   \u003Clink rel=\"stylesheet\" href=\"..\u002F..\u002F..\u002Fplayground\u002Fassets\u002Fbase.css\" \u002F>\n *\n * The relative path resolves the same locally (posts\u002F\u003Cbase>\u002Fplayground\u002F) and on\n * the deployed host (public\u002Fposts\u002F\u003Cbase>\u002Fplayground\u002F), because build-site.js\n * mirrors this file to public\u002Fplayground\u002Fassets\u002Fbase.css. For a CodeSandbox\n * --embed, playground.js inlines this file so the single-file sandbox still styles.\n *\n * Then write ONLY the demo-specific CSS in your inline \u003Cstyle>. Everything below\n * — tokens, layout, panels, buttons, toggles, sliders, code blocks, status\u002Flog,\n * banners, presets — comes for free and looks consistent across every post.\n *\n * Theme-aware: dark by default, light via prefers-color-scheme AND a\n * [data-theme] override on \u003Chtml> (so a toggle can force either). Accessible:\n * real focus rings, adequate contrast, reduced-motion honored.\n *\u002F\n\n\u002F* ---------- design tokens ---------- *\u002F\n:root {\n  --bg: #0d1117;\n  --bg-grid: #ffffff0a;\n  --panel: #161b22;\n  --panel-2: #0b0e14;\n  --card: #0b0e14;\n  --ink: #e8ebf2;\n  --muted: #9aa4b2;\n  --faint: #6b7688;\n  --line: #232a35;\n  --line-soft: #ffffff12;\n  --accent: #7c9cff;\n  --accent-ink: #0b0e14;\n  --good: #3fb950;\n  --warn: #f0883e;\n  --bad: #f85149;\n  --info: #58a6ff;\n  --radius: 14px;\n  --radius-sm: 9px;\n  --shadow: 0 8px 30px #0006;\n  --shadow-sm: 0 4px 14px #0005;\n  --mono: ui-monospace, SFMono-Regular, \"SF Mono\", Menlo, Consolas, \"Liberation Mono\", monospace;\n  --sans: ui-sans-serif, system-ui, -apple-system, \"Segoe UI\", Roboto, \"Helvetica Neue\", sans-serif;\n  color-scheme: dark;\n}\n\n\u002F* Light theme — system preference, overridable by [data-theme] on \u003Chtml>. *\u002F\n@media (prefers-color-scheme: light) {\n  :root:not([data-theme=\"dark\"]) {\n    --bg: #f4f6fb;\n    --bg-grid: #00000008;\n    --panel: #ffffff;\n    --panel-2: #f0f3f9;\n    --card: #f7f9fc;\n    --ink: #131722;\n    --muted: #5b6472;\n    --faint: #8a93a3;\n    --line: #e2e7f0;\n    --line-soft: #00000010;\n    --accent: #2f6df0;\n    --accent-ink: #ffffff;\n    --good: #1a7f37;\n    --warn: #bc4c00;\n    --bad: #cf222e;\n    --info: #0969da;\n    --shadow: 0 8px 30px #0000001f;\n    --shadow-sm: 0 4px 14px #00000014;\n    color-scheme: light;\n  }\n}\n:root[data-theme=\"light\"] {\n  --bg: #f4f6fb;\n  --bg-grid: #00000008;\n  --panel: #ffffff;\n  --panel-2: #f0f3f9;\n  --card: #f7f9fc;\n  --ink: #131722;\n  --muted: #5b6472;\n  --faint: #8a93a3;\n  --line: #e2e7f0;\n  --line-soft: #00000010;\n  --accent: #2f6df0;\n  --accent-ink: #ffffff;\n  --good: #1a7f37;\n  --warn: #bc4c00;\n  --bad: #cf222e;\n  --info: #0969da;\n  --shadow: 0 8px 30px #0000001f;\n  --shadow-sm: 0 4px 14px #00000014;\n  color-scheme: light;\n}\n\n\u002F* ---------- reset & base ---------- *\u002F\n*, *::before, *::after { box-sizing: border-box; }\n\nbody {\n  margin: 0;\n  min-height: 100vh;\n  font-family: var(--sans);\n  color: var(--ink);\n  background:\n    radial-gradient(circle at 1px 1px, var(--bg-grid) 1px, transparent 0) 0 0 \u002F 24px 24px,\n    var(--bg);\n  display: flex;\n  justify-content: center;\n  align-items: flex-start;\n  padding: clamp(14px, 3vw, 26px);\n  line-height: 1.55;\n  -webkit-font-smoothing: antialiased;\n  text-rendering: optimizeLegibility;\n}\n\n\u002F* The single content column. *\u002F\n.pg {\n  width: 100%;\n  max-width: 860px;\n}\n\n\u002F* ---------- header ---------- *\u002F\n.pg-title {\n  font-size: clamp(1.15rem, 1rem + 1vw, 1.4rem);\n  font-weight: 800;\n  letter-spacing: -0.02em;\n  margin: 0 0 4px;\n  display: flex;\n  align-items: center;\n  gap: 9px;\n}\n.pg-sub {\n  color: var(--muted);\n  font-size: 0.92rem;\n  line-height: 1.5;\n  margin: 0 0 16px;\n  max-width: 66ch;\n}\n.pg-sub strong, .pg-sub b { color: var(--ink); font-weight: 700; }\n.pg-sub code { font-family: var(--mono); background: var(--line-soft); color: var(--accent);\n  padding: 1px 6px; border-radius: 6px; font-size: 0.85em; }\n\n\u002F* ---------- panels ---------- *\u002F\n.panel {\n  background: var(--panel);\n  border: 1px solid var(--line);\n  border-radius: var(--radius);\n  padding: 16px 18px;\n  margin-bottom: 14px;\n  box-shadow: var(--shadow-sm);\n}\n.panel-label {\n  font-size: 0.7rem;\n  text-transform: uppercase;\n  letter-spacing: 0.08em;\n  color: var(--muted);\n  font-weight: 800;\n  margin: 0 0 13px;\n  display: flex;\n  align-items: center;\n  gap: 8px;\n}\n.panel-label .n {\n  display: inline-grid; place-items: center;\n  width: 18px; height: 18px; border-radius: 50%;\n  background: var(--accent); color: var(--accent-ink);\n  font-size: 0.66rem; font-weight: 800;\n}\n\n\u002F* ---------- layout helpers ---------- *\u002F\n.row { display: flex; flex-wrap: wrap; gap: 12px; align-items: center; }\n.row.between { justify-content: space-between; }\n.col { display: flex; flex-direction: column; gap: 10px; }\n.grow { flex: 1 1 0; min-width: 0; }\n.wrap-controls { display: flex; flex-wrap: wrap; gap: 16px 24px; align-items: flex-end; }\n.field { display: flex; flex-direction: column; gap: 7px; min-width: 0; }\n.field > .label, .ctl-label {\n  font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.04em;\n  color: var(--muted); font-weight: 800;\n}\n\n\u002F* ---------- buttons ---------- *\u002F\n.btn {\n  font: inherit; font-weight: 650; font-size: 0.88rem;\n  cursor: pointer; user-select: none;\n  border: 1px solid var(--line);\n  background: var(--card); color: var(--ink);\n  padding: 9px 15px; border-radius: var(--radius-sm);\n  display: inline-flex; align-items: center; gap: 8px;\n  transition: background .15s ease, border-color .15s ease, transform .05s ease, color .15s ease;\n}\n.btn:hover { background: var(--line-soft); border-color: var(--muted); }\n.btn:active { transform: translateY(1px); }\n.btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }\n.btn[disabled] { opacity: 0.45; cursor: not-allowed; }\n.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }\n.btn.primary:hover { filter: brightness(1.08); background: var(--accent); }\n.btn.good { background: var(--good); border-color: var(--good); color: #04140a; }\n.btn.bad  { background: var(--bad);  border-color: var(--bad);  color: #fff; }\n.btn.ghost { background: transparent; }\n.btn.sm { padding: 6px 11px; font-size: 0.82rem; }\n\n.btn-row { display: flex; flex-wrap: wrap; gap: 9px; }\n\n\u002F* Segmented control — a row of buttons where one is active (aria-pressed). *\u002F\n.seg { display: inline-flex; background: var(--card); border: 1px solid var(--line);\n  border-radius: var(--radius-sm); padding: 3px; gap: 3px; }\n.seg button {\n  font: inherit; font-weight: 650; font-size: 0.84rem; cursor: pointer;\n  border: none; background: transparent; color: var(--muted);\n  padding: 7px 13px; border-radius: 7px;\n  transition: background .15s ease, color .15s ease;\n}\n.seg button:hover { color: var(--ink); }\n.seg button[aria-pressed=\"true\"] { background: var(--accent); color: var(--accent-ink); }\n.seg button:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }\n\n\u002F* Preset chips — worked-example shortcuts. *\u002F\n.presets { display: flex; flex-wrap: wrap; gap: 8px; }\n.presets .btn { background: var(--panel-2); }\n\n\u002F* ---------- toggle switch ---------- *\u002F\n.toggle { display: inline-flex; align-items: center; gap: 10px; cursor: pointer;\n  font-size: 0.88rem; font-weight: 600; user-select: none; }\n.toggle input { position: absolute; opacity: 0; width: 0; height: 0; }\n.switch { position: relative; width: 44px; height: 25px; border-radius: 999px; flex: none;\n  background: var(--line); border: 1px solid var(--line); transition: background .18s ease; }\n.switch::after { content: \"\"; position: absolute; top: 2px; left: 2px; width: 19px; height: 19px;\n  border-radius: 50%; background: #cfd6e4; transition: transform .18s ease; box-shadow: 0 1px 3px #0006; }\n.toggle input:checked + .switch { background: var(--good); border-color: var(--good); }\n.toggle input:checked + .switch::after { transform: translateX(19px); background: #fff; }\n.toggle input:focus-visible + .switch { outline: 2px solid var(--accent); outline-offset: 2px; }\n\n\u002F* ---------- range slider ---------- *\u002F\ninput[type=\"range\"] {\n  -webkit-appearance: none; appearance: none; width: 100%; height: 6px;\n  background: var(--line); border-radius: 999px; outline: none; cursor: pointer; margin: 8px 0;\n}\ninput[type=\"range\"]::-webkit-slider-thumb {\n  -webkit-appearance: none; appearance: none; width: 19px; height: 19px; border-radius: 50%;\n  background: var(--accent); border: 2px solid var(--panel); box-shadow: var(--shadow-sm); cursor: pointer;\n}\ninput[type=\"range\"]::-moz-range-thumb {\n  width: 19px; height: 19px; border-radius: 50%; background: var(--accent);\n  border: 2px solid var(--panel); box-shadow: var(--shadow-sm); cursor: pointer;\n}\ninput[type=\"range\"]:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; }\n\n\u002F* ---------- text inputs \u002F selects ---------- *\u002F\ninput[type=\"text\"], input[type=\"number\"], input[type=\"search\"], select, textarea {\n  font: inherit; color: var(--ink); background: var(--card);\n  border: 1px solid var(--line); border-radius: var(--radius-sm); padding: 8px 11px; width: 100%;\n}\ntextarea { font-family: var(--mono); font-size: 0.85rem; line-height: 1.6; resize: vertical; }\ninput:focus-visible, select:focus-visible, textarea:focus-visible {\n  outline: 2px solid var(--accent); outline-offset: 1px; border-color: var(--accent);\n}\n\n\u002F* ---------- status \u002F output \u002F log ---------- *\u002F\n.status {\n  display: flex; align-items: center; gap: 9px; flex-wrap: wrap;\n  font-size: 0.9rem; font-weight: 600;\n  padding: 11px 14px; border-radius: var(--radius-sm);\n  background: var(--panel-2); border: 1px solid var(--line); color: var(--ink);\n}\n.status.good { border-color: color-mix(in srgb, var(--good) 55%, var(--line)); }\n.status.warn { border-color: color-mix(in srgb, var(--warn) 55%, var(--line)); }\n.status.bad  { border-color: color-mix(in srgb, var(--bad) 55%, var(--line)); }\n.dot { width: 9px; height: 9px; border-radius: 50%; background: var(--muted); flex: none; }\n.dot.good { background: var(--good); } .dot.warn { background: var(--warn); }\n.dot.bad { background: var(--bad); } .dot.info { background: var(--info); }\n\n.output { background: var(--panel-2); border: 1px solid var(--line); border-radius: var(--radius-sm);\n  padding: 13px 15px; }\n.log { font-family: var(--mono); font-size: 0.8rem; line-height: 1.7; background: var(--card);\n  border: 1px solid var(--line); border-radius: var(--radius-sm); padding: 11px 14px;\n  max-height: 220px; overflow-y: auto; white-space: pre-wrap; }\n\n\u002F* ---------- code block + syntax tokens ---------- *\u002F\n.code {\n  font-family: var(--mono); font-size: 0.82rem; line-height: 1.7;\n  background: var(--panel-2); border: 1px solid var(--line); border-radius: var(--radius-sm);\n  padding: 13px 15px; overflow-x: auto; white-space: pre; tab-size: 2;\n}\n.code .tok-sel  { color: var(--accent); }\n.code .tok-prop { color: #86e29b; }\n.code .tok-kw   { color: #ff9bcb; }\n.code .tok-str  { color: #f0c674; }\n.code .tok-num  { color: #f0883e; }\n.code .tok-cmt  { color: var(--faint); font-style: italic; }\n.code .hl { background: color-mix(in srgb, var(--good) 22%, transparent); border-radius: 4px; padding: 0 3px; }\n\n\u002F* ---------- hint \u002F caption ---------- *\u002F\n.hint { font-size: 0.83rem; color: var(--muted); line-height: 1.55; margin: 10px 0 0; }\n.hint code { font-family: var(--mono); color: var(--ink); background: var(--line-soft);\n  padding: 1px 5px; border-radius: 5px; font-size: 0.86em; }\n.hint strong { color: var(--ink); }\n\n\u002F* ---------- banner (feature-support \u002F notices) ---------- *\u002F\n.banner {\n  display: none; margin-bottom: 14px; padding: 11px 14px; border-radius: 11px;\n  font-size: 0.85rem; line-height: 1.5;\n  color: var(--ink); background: color-mix(in srgb, var(--warn) 12%, var(--panel));\n  border: 1px solid color-mix(in srgb, var(--warn) 45%, var(--line));\n}\n.banner.show { display: block; }\n.banner.info { background: color-mix(in srgb, var(--info) 12%, var(--panel));\n  border-color: color-mix(in srgb, var(--info) 45%, var(--line)); }\n.banner code { font-family: var(--mono); background: var(--line-soft); padding: 1px 5px; border-radius: 5px; }\n\n\u002F* ---------- misc atoms ---------- *\u002F\n.pill { display: inline-flex; align-items: center; gap: 6px; font-size: 0.75rem; font-weight: 700;\n  padding: 3px 9px; border-radius: 999px; background: var(--line-soft); color: var(--muted); }\n.pill.good { color: var(--good); background: color-mix(in srgb, var(--good) 16%, transparent); }\n.pill.bad  { color: var(--bad);  background: color-mix(in srgb, var(--bad) 16%, transparent); }\n.mono { font-family: var(--mono); }\n.muted { color: var(--muted); }\n.big-num { font-family: var(--mono); font-size: 1.6rem; font-weight: 800; letter-spacing: -0.02em; }\n\n\u002F* Optional theme toggle button (top-right). Wire it in JS if you want it. *\u002F\n.theme-btn { position: fixed; top: 12px; right: 12px; z-index: 20; }\n\n\u002F* ---------- responsive ---------- *\u002F\n@media (max-width: 560px) {\n  .panel { padding: 14px; }\n  .wrap-controls { gap: 14px; }\n  .btn { padding: 9px 13px; }\n}\n\n\u002F* ---------- reduced motion ---------- *\u002F\n@media (prefers-reduced-motion: reduce) {\n  *, *::before, *::after { transition-duration: 0.01ms !important; animation-duration: 0.01ms !important; }\n}\n\n\n.rowstage {\n    position: absolute;\n    width: 1px;\n    height: 1px;\n    overflow: hidden;\n    opacity: 0;\n    pointer-events: none;\n  }\n  .frame-bar {\n    display: flex;\n    height: 28px;\n    border-radius: var(--radius-sm);\n    overflow: hidden;\n    border: 1px solid var(--line);\n    margin-top: 10px;\n  }\n  .frame-bar span {\n    display: block;\n    height: 100%;\n  }\n  .seg-script { background: var(--accent); }\n  .seg-layout { background: #e0485a; }\n  .seg-idle { background: var(--panel-2); }\n  .legend {\n    display: flex;\n    gap: 16px;\n    margin-top: 8px;\n    font-size: .78rem;\n    color: var(--muted);\n  }\n  .legend span { display: inline-flex; align-items: center; gap: 6px; }\n  .swatch { width: 10px; height: 10px; border-radius: 3px; display: inline-block; }\n  .script-row {\n    display: grid;\n    grid-template-columns: 1fr auto auto;\n    gap: 8px;\n    padding: 6px 0;\n    border-bottom: 1px dashed var(--line);\n    font-size: .85rem;\n  }\n  .script-row:last-child { border-bottom: none; }","\"use strict\";\n  const $ = (id) => document.getElementById(id);\n  const stage = $(\"stage\");\n\n  const state = { mode: \"interleaved\", count: 800 };\n\n  const MODE_HINT = {\n    interleaved: \"Each row's height is set, then its height is immediately read back — once per row. That read forces the browser to recompute layout before it can answer.\",\n    batched: \"Every row's height is set first. Only after the loop finishes does anything read a size back — so layout is recomputed once, not once per row.\",\n  };\n\n  const CODE = `new PerformanceObserver((list) => {\n  for (const entry of list.getEntries()) {\n    console.log(\"frame:\", entry.duration, \"ms\");\n    console.log(\"blocked input:\", entry.blockingDuration, \"ms\");\n    for (const s of entry.scripts) {\n      console.log(s.invoker, s.duration, s.forcedStyleAndLayoutDuration);\n    }\n  }\n}).observe({ type: \"long-animation-frame\", buffered: true });`;\n\n  \u002F\u002F Build a hidden stage of rows so the handler has something real to touch.\n  function buildStage(n) {\n    stage.innerHTML = \"\";\n    const frag = document.createDocumentFragment();\n    for (let i = 0; i \u003C n; i++) {\n      const row = document.createElement(\"div\");\n      row.style.height = \"20px\";\n      frag.appendChild(row);\n    }\n    stage.appendChild(frag);\n  }\n\n  function interleavedHandler() {\n    const rows = stage.children;\n    let total = 0;\n    for (let i = 0; i \u003C rows.length; i++) {\n      rows[i].style.height = 20 + (i % 7) + \"px\";\n      total += rows[i].offsetHeight; \u002F\u002F forces layout — every single iteration\n    }\n    return total;\n  }\n\n  function batchedHandler() {\n    const rows = stage.children;\n    for (let i = 0; i \u003C rows.length; i++) {\n      rows[i].style.height = 20 + (i % 7) + \"px\";\n    }\n    let total = 0;\n    for (let i = 0; i \u003C rows.length; i++) {\n      total += rows[i].offsetHeight; \u002F\u002F forces layout once, after every write is queued\n    }\n    return total;\n  }\n\n  function setStatus(cls, text) {\n    $(\"dot\").className = \"dot \" + cls;\n    $(\"statusText\").textContent = text;\n  }\n\n  function renderBar(scriptMs, layoutMs, frameMs) {\n    const bar = $(\"frameBar\");\n    bar.innerHTML = \"\";\n    const idleMs = Math.max(0, frameMs - scriptMs - layoutMs);\n    const total = Math.max(frameMs, 1);\n    const make = (cls, ms) => {\n      const span = document.createElement(\"span\");\n      span.className = cls;\n      span.style.width = Math.max(0, (ms \u002F total) * 100) + \"%\";\n      bar.appendChild(span);\n    };\n    make(\"seg-script\", Math.max(0, scriptMs - layoutMs));\n    make(\"seg-layout\", layoutMs);\n    make(\"seg-idle\", idleMs);\n  }\n\n  function renderBreakdown(rows) {\n    const el = $(\"breakdown\");\n    el.innerHTML = \"\";\n    if (!rows.length) {\n      el.textContent = \"No per-script attribution available in this browser — see the caveat below.\";\n      return;\n    }\n    rows.forEach((r) => {\n      const div = document.createElement(\"div\");\n      div.className = \"script-row\";\n      div.innerHTML =\n        \"\u003Cspan>\" + r.invoker + \"\u003C\u002Fspan>\" +\n        \"\u003Cspan class='mono'>\" + r.duration.toFixed(1) + \"ms script\u003C\u002Fspan>\" +\n        \"\u003Cspan class='mono'>\" + r.forced.toFixed(1) + \"ms forced layout\u003C\u002Fspan>\";\n      el.appendChild(div);\n    });\n  }\n\n  \u002F\u002F Pull-based on purpose: a long synchronous handler blocks the main thread for its\n  \u002F\u002F entire run, so a push-based observer callback races a fallback timeout and can\n  \u002F\u002F lose even when the frame genuinely took seconds. Instead: run the handler, let\n  \u002F\u002F the browser get a turn to report (retrying once — reporting can lag on a very\n  \u002F\u002F busy page), then read the buffered entries directly.\n  async function readLoAFEntry(markStart) {\n    for (const waitMs of [700, 1200]) {\n      await new Promise((resolve) => setTimeout(resolve, waitMs));\n      const entries = performance\n        .getEntriesByType(\"long-animation-frame\")\n        .filter((e) => e.startTime >= markStart - 1);\n      if (entries.length) return entries[entries.length - 1];\n    }\n    return null;\n  }\n\n  async function run() {\n    const handler = state.mode === \"interleaved\" ? interleavedHandler : batchedHandler;\n    const supportsLoAF = \"PerformanceObserver\" in window &&\n      PerformanceObserver.supportedEntryTypes &&\n      PerformanceObserver.supportedEntryTypes.includes(\"long-animation-frame\");\n\n    setStatus(\"info\", \"Running the handler on \" + state.count + \" rows…\");\n    $(\"runBtn\").disabled = true;\n    \u002F\u002F Yield one tick so the \"Running…\" status actually paints before the freeze.\n    await new Promise((resolve) => setTimeout(resolve, 20));\n    buildStage(state.count);\n\n    if (supportsLoAF) {\n      const obs = new PerformanceObserver(() => {}); \u002F\u002F keeps entries buffered even pre-observe\n      obs.observe({ type: \"long-animation-frame\", buffered: true });\n      const markStart = performance.now();\n      handler();\n      const entry = await readLoAFEntry(markStart);\n      obs.disconnect();\n      $(\"runBtn\").disabled = false;\n      if (!entry) {\n        setStatus(\"warn\", \"Frame finished in under 50ms — too fast to count as a long animation frame. Try more rows.\");\n        renderBar(0, 0, 1);\n        renderBreakdown([]);\n        return;\n      }\n      const scripts = entry.scripts || [];\n      const rows = scripts.map((s) => ({\n        invoker: s.invoker || \"(no invoker reported)\",\n        duration: s.duration || 0,\n        forced: s.forcedStyleAndLayoutDuration || 0,\n      }));\n      const scriptMs = rows.reduce((a, r) => a + r.duration, 0);\n      const layoutMs = rows.reduce((a, r) => a + r.forced, 0);\n      renderBar(scriptMs, layoutMs, entry.duration);\n      renderBreakdown(rows);\n      const verdict = layoutMs > entry.duration * 0.25\n        ? \"bad\"\n        : entry.duration > 50 ? \"warn\" : \"good\";\n      setStatus(\n        verdict,\n        \"Frame took \" + entry.duration.toFixed(0) + \"ms, blocked input for \" + entry.blockingDuration.toFixed(0) +\n        \"ms, and \" + layoutMs.toFixed(0) + \"ms of that was forced layout.\"\n      );\n    } else {\n      const t0 = performance.now();\n      handler();\n      const t1 = performance.now();\n      $(\"runBtn\").disabled = false;\n      renderBar(t1 - t0, 0, Math.max(t1 - t0, 1));\n      renderBreakdown([]);\n      setStatus(\n        \"warn\",\n        \"Handler took \" + (t1 - t0).toFixed(1) + \"ms (measured manually). Your browser doesn't support the \" +\n        \"Long Animation Frames API yet, so no per-script attribution is available — see the honest caveat in the post.\"\n      );\n    }\n  }\n\n  document.querySelectorAll(\"#modeSeg button\").forEach((btn) => {\n    btn.addEventListener(\"click\", () => {\n      state.mode = btn.dataset.mode;\n      document.querySelectorAll(\"#modeSeg button\").forEach((b) => b.setAttribute(\"aria-pressed\", String(b === btn)));\n      $(\"modeHint\").textContent = MODE_HINT[state.mode];\n    });\n  });\n\n  $(\"count\").addEventListener(\"input\", (e) => {\n    state.count = Number(e.target.value);\n    $(\"countLabel\").textContent = state.count;\n  });\n\n  document.querySelectorAll(\"[data-count]\").forEach((btn) => {\n    btn.addEventListener(\"click\", () => {\n      state.count = Number(btn.dataset.count);\n      $(\"count\").value = state.count;\n      $(\"countLabel\").textContent = state.count;\n    });\n  });\n\n  $(\"runBtn\").addEventListener(\"click\", run);\n  $(\"codeOut\").textContent = CODE;\n  buildStage(state.count);",{"height":52,"autorun":17},520,{"slug":45,"title":54,"excerpt":55,"coverUrl":56,"vertical":57},"Your Lighthouse Score Is 100. Long Animation Frames Explain the Jank.","Lighthouse says 100 and CI is green, but a user still says the filter button feels sluggish. The Long Animation Frames API names the exact script and phase that blocked the frame — here's how to read it instead of squinting at a flame chart.","\u002Fmedia\u002Fcovers\u002Flong-animation-frames-api.png",{"slug":6},[59,63,67,71,75,79,83,86,90,94,97,101],{"slug":60,"name":61,"articles":62},"webdev","Webdev",133,{"slug":64,"name":65,"articles":66},"javascript","Javascript",109,{"slug":68,"name":69,"articles":70},"frontend","Frontend",82,{"slug":72,"name":73,"articles":74},"tutorial","Tutorial",51,{"slug":76,"name":77,"articles":78},"css","Css",42,{"slug":80,"name":81,"articles":82},"performance","Performance",18,{"slug":84,"name":85,"articles":82},"typescript","Typescript",{"slug":87,"name":88,"articles":89},"react","React",16,{"slug":91,"name":92,"articles":93},"browser","Browser",12,{"slug":95,"name":96,"articles":93},"node","Node",{"slug":98,"name":99,"articles":100},"accessibility","Accessibility",9,{"slug":102,"name":103,"articles":100},"programming","Programming"]