[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"verticals":3,"playground-navigator-sendbeacon-reliable-analytics":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},"navigator-sendbeacon-reliable-analytics","navigator.sendBeacon — interactive playground",null,"\u003Cdiv class=\"pg-shell\">\n  \u003Cheader class=\"pg-header\">\n    \u003Cdiv class=\"pg-badge\">navigator.sendBeacon\u003C\u002Fdiv>\n    \u003Ch1 class=\"pg-title\">Reliable analytics on page exit\u003C\u002Fh1>\n    \u003Cp class=\"pg-subtitle\">Trigger events, then \"navigate away\" to see the delivery difference between fetch and sendBeacon.\u003C\u002Fp>\n  \u003C\u002Fheader>\n\n  \u003Cmain class=\"pg-main\">\n\n    \u003C!-- Mode toggle -->\n    \u003Cdiv class=\"scenario-toggle\">\n      \u003Cbutton class=\"scenario-btn active\" id=\"btn-beacon\" onclick=\"setMode('beacon')\">\n        ✅ sendBeacon (guaranteed)\n      \u003C\u002Fbutton>\n      \u003Cbutton class=\"scenario-btn\" id=\"btn-fetch\" onclick=\"setMode('fetch')\">\n        ⚠️ fetch in beforeunload\n      \u003C\u002Fbutton>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"session-panel\">\n      \u003C!-- Left: event triggers -->\n      \u003Cdiv class=\"panel-box\">\n        \u003Ch3>Session events\u003C\u002Fh3>\n        \u003Cdiv class=\"event-btns\">\n          \u003Cbutton class=\"event-btn\" onclick=\"addEvent('page_view')\">\n            \u003Cspan class=\"icon\">👁️\u003C\u002Fspan>\n            \u003Cspan class=\"label\">Page view\u003C\u002Fspan>\n            \u003Cspan class=\"count\" id=\"cnt-page_view\">0\u003C\u002Fspan>\n          \u003C\u002Fbutton>\n          \u003Cbutton class=\"event-btn\" onclick=\"addEvent('click')\">\n            \u003Cspan class=\"icon\">🖱️\u003C\u002Fspan>\n            \u003Cspan class=\"label\">Button click\u003C\u002Fspan>\n            \u003Cspan class=\"count\" id=\"cnt-click\">0\u003C\u002Fspan>\n          \u003C\u002Fbutton>\n          \u003Cbutton class=\"event-btn\" onclick=\"addEvent('scroll_depth')\">\n            \u003Cspan class=\"icon\">📜\u003C\u002Fspan>\n            \u003Cspan class=\"label\">Scroll depth\u003C\u002Fspan>\n            \u003Cspan class=\"count\" id=\"cnt-scroll_depth\">0\u003C\u002Fspan>\n          \u003C\u002Fbutton>\n          \u003Cbutton class=\"event-btn\" onclick=\"addEvent('search')\">\n            \u003Cspan class=\"icon\">🔍\u003C\u002Fspan>\n            \u003Cspan class=\"label\">Search query\u003C\u002Fspan>\n            \u003Cspan class=\"count\" id=\"cnt-search\">0\u003C\u002Fspan>\n          \u003C\u002Fbutton>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n\n      \u003C!-- Right: queue + exit -->\n      \u003Cdiv class=\"panel-box\">\n        \u003Ch3>Event queue\u003C\u002Fh3>\n        \u003Cdiv class=\"queue-box\" id=\"queue-log\">\n          \u003Cspan style=\"color:var(--faint);font-style:italic\">Queue is empty — trigger some events\u003C\u002Fspan>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"queue-count\">Queued: \u003Cspan id=\"queue-size\">0\u003C\u002Fspan> event(s)\u003C\u002Fdiv>\n        \u003Cbutton class=\"exit-btn\" id=\"exit-btn\" onclick=\"simulateExit()\" disabled>\n          🚪 Navigate away (flush analytics)\n        \u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003C!-- Network log -->\n    \u003Cdiv class=\"panel-box\">\n      \u003Ch3>Network \u002F delivery log\u003C\u002Fh3>\n      \u003Cdiv class=\"network-log\" id=\"net-log\">\n        \u003Cspan style=\"color:var(--faint);font-style:italic\">Delivery log appears here after navigating away\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003C!-- Explanation -->\n    \u003Cdiv class=\"explanation\" id=\"explanation\">\n      \u003Cstrong>sendBeacon mode:\u003C\u002Fstrong> When you click \"Navigate away\", the queue is flushed with\n      \u003Ccode>navigator.sendBeacon('\u002Fanalytics\u002Fbatch', blob)\u003C\u002Fcode>. The browser queues the POST and\n      delivers it even as the page is torn down. The return value (\u003Ccode>true\u003C\u002Fcode>) confirms it was accepted.\n    \u003C\u002Fdiv>\n\n    \u003C!-- Code preview -->\n    \u003Cdiv class=\"code-block\" id=\"code-preview\">\u003Cspan class=\"cm\">\u002F\u002F visibilitychange + sendBeacon pattern\u003C\u002Fspan>\n\u003Cspan class=\"kw\">const\u003C\u002Fspan> eventQueue = [];\n\n\u003Cspan class=\"fn\">document\u003C\u002Fspan>.\u003Cspan class=\"fn\">addEventListener\u003C\u002Fspan>(\u003Cspan class=\"str\">'visibilitychange'\u003C\u002Fspan>, () => {\n  \u003Cspan class=\"kw\">if\u003C\u002Fspan> (\u003Cspan class=\"fn\">document\u003C\u002Fspan>.visibilityState === \u003Cspan class=\"str\">'hidden'\u003C\u002Fspan>) {\n    \u003Cspan class=\"kw\">const\u003C\u002Fspan> body = \u003Cspan class=\"kw\">new\u003C\u002Fspan> \u003Cspan class=\"fn\">Blob\u003C\u002Fspan>(\n      [\u003Cspan class=\"fn\">JSON\u003C\u002Fspan>.stringify(eventQueue)],\n      { type: \u003Cspan class=\"str\">'application\u002Fjson'\u003C\u002Fspan> }\n    );\n    navigator.\u003Cspan class=\"fn\">sendBeacon\u003C\u002Fspan>(\u003Cspan class=\"str\">'\u002Fanalytics\u002Fbatch'\u003C\u002Fspan>, body);\n  }\n});\u003C\u002Fdiv>\n\n    \u003Cbutton class=\"reset-btn\" onclick=\"resetAll()\">↺ Reset playground\u003C\u002Fbutton>\n  \u003C\u002Fmain>\n\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.scenario-toggle {\n    display: flex;\n    gap: 8px;\n    margin-bottom: 20px;\n  }\n  .scenario-btn {\n    flex: 1;\n    padding: 10px 14px;\n    border: 2px solid var(--line);\n    border-radius: var(--radius-sm);\n    background: var(--panel-2);\n    color: var(--muted);\n    font: 600 0.8rem var(--sans);\n    cursor: pointer;\n    transition: border-color 0.15s, color 0.15s, background 0.15s;\n    text-align: center;\n  }\n  .scenario-btn.active {\n    border-color: var(--accent);\n    color: var(--accent);\n    background: color-mix(in srgb, var(--accent) 10%, var(--panel-2));\n  }\n\n  .session-panel {\n    display: grid;\n    grid-template-columns: 1fr 1fr;\n    gap: 14px;\n    margin-bottom: 16px;\n  }\n  @media (max-width: 560px) {\n    .session-panel { grid-template-columns: 1fr; }\n  }\n\n  .panel-box {\n    background: var(--panel-2);\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    padding: 14px;\n  }\n  .panel-box h3 {\n    margin: 0 0 10px;\n    font-size: 0.75rem;\n    font-weight: 700;\n    color: var(--muted);\n    letter-spacing: 0.06em;\n    text-transform: uppercase;\n  }\n\n  .event-btns {\n    display: flex;\n    flex-direction: column;\n    gap: 8px;\n  }\n  .event-btn {\n    display: flex;\n    align-items: center;\n    gap: 10px;\n    padding: 9px 12px;\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    background: var(--panel);\n    color: var(--ink);\n    font: 500 0.8rem var(--sans);\n    cursor: pointer;\n    transition: border-color 0.12s, background 0.12s;\n    text-align: left;\n  }\n  .event-btn:hover { border-color: var(--accent); background: color-mix(in srgb, var(--accent) 6%, var(--panel)); }\n  .event-btn .icon { font-size: 1.1rem; }\n  .event-btn .label { flex: 1; }\n  .event-btn .count {\n    font: 700 0.75rem var(--mono);\n    color: var(--accent);\n    min-width: 2ch;\n    text-align: right;\n  }\n\n  .queue-box {\n    background: var(--bg);\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    min-height: 120px;\n    max-height: 160px;\n    overflow-y: auto;\n    padding: 8px 10px;\n    font: 0.77rem\u002F1.7 var(--mono);\n    margin-bottom: 10px;\n  }\n  .queue-entry {\n    display: flex;\n    gap: 8px;\n    align-items: baseline;\n    padding: 1px 0;\n    border-bottom: 1px solid var(--line-soft);\n    animation: fadein 0.2s ease;\n  }\n  .queue-entry:last-child { border-bottom: none; }\n  @keyframes fadein { from { opacity: 0; transform: translateY(3px); } to { opacity: 1; } }\n  .queue-entry .ts { color: var(--faint); min-width: 5ch; }\n  .queue-entry .ev { color: var(--accent); }\n  .queue-count {\n    font: 600 0.75rem var(--sans);\n    color: var(--muted);\n    margin-bottom: 10px;\n  }\n  .queue-count span { color: var(--accent); font-weight: 700; }\n\n  .exit-btn {\n    width: 100%;\n    padding: 11px;\n    border: none;\n    border-radius: var(--radius-sm);\n    background: var(--bad);\n    color: #fff;\n    font: 700 0.85rem var(--sans);\n    cursor: pointer;\n    letter-spacing: 0.03em;\n    transition: opacity 0.15s;\n  }\n  .exit-btn:hover { opacity: 0.85; }\n  .exit-btn:disabled { opacity: 0.4; cursor: not-allowed; }\n\n  .network-log {\n    background: var(--bg);\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    min-height: 100px;\n    max-height: 200px;\n    overflow-y: auto;\n    padding: 8px 10px;\n    font: 0.77rem\u002F1.7 var(--mono);\n  }\n  .net-entry {\n    display: flex;\n    align-items: baseline;\n    gap: 8px;\n    padding: 2px 0;\n    border-bottom: 1px solid var(--line-soft);\n    animation: fadein 0.2s ease;\n  }\n  .net-entry:last-child { border-bottom: none; }\n  .net-entry .badge {\n    font: 700 0.68rem var(--sans);\n    padding: 1px 5px;\n    border-radius: 4px;\n    white-space: nowrap;\n  }\n  .badge-sent { background: color-mix(in srgb, var(--good) 20%, transparent); color: var(--good); }\n  .badge-cancelled { background: color-mix(in srgb, var(--bad) 20%, transparent); color: var(--bad); }\n  .badge-queued { background: color-mix(in srgb, var(--info) 20%, transparent); color: var(--info); }\n  .net-entry .net-msg { color: var(--ink); }\n  .net-entry .net-sub { color: var(--faint); font-size: 0.72rem; }\n\n  .explanation {\n    background: color-mix(in srgb, var(--accent) 8%, var(--panel));\n    border: 1px solid color-mix(in srgb, var(--accent) 30%, var(--line));\n    border-radius: var(--radius-sm);\n    padding: 12px 14px;\n    font-size: 0.8rem;\n    line-height: 1.6;\n    color: var(--muted);\n    margin-top: 14px;\n  }\n  .explanation strong { color: var(--ink); }\n\n  .code-block {\n    background: var(--bg);\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    padding: 10px 12px;\n    font: 0.77rem\u002F1.7 var(--mono);\n    color: var(--ink);\n    overflow-x: auto;\n    margin-top: 14px;\n    white-space: pre;\n  }\n  .kw { color: #7c9cff; }\n  .fn { color: #e2a860; }\n  .str { color: #7ec187; }\n  .cm { color: var(--faint); }\n  .reset-btn {\n    margin-top: 14px;\n    padding: 8px 16px;\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    background: var(--panel);\n    color: var(--muted);\n    font: 600 0.78rem var(--sans);\n    cursor: pointer;\n  }\n  .reset-btn:hover { border-color: var(--accent); color: var(--accent); }","let mode = 'beacon';\n  let eventQueue = [];\n  let eventCounts = { page_view: 0, click: 0, scroll_depth: 0, search: 0 };\n  let sessionStart = Date.now();\n\n  const labels = {\n    page_view: 'page_view',\n    click: 'button_click',\n    scroll_depth: 'scroll_50pct',\n    search: 'search_query',\n  };\n\n  function ts() {\n    const s = ((Date.now() - sessionStart) \u002F 1000).toFixed(1);\n    return s + 's';\n  }\n\n  function setMode(m) {\n    mode = m;\n    document.getElementById('btn-beacon').classList.toggle('active', m === 'beacon');\n    document.getElementById('btn-fetch').classList.toggle('active', m === 'fetch');\n\n    const expl = document.getElementById('explanation');\n    const code = document.getElementById('code-preview');\n    if (m === 'beacon') {\n      expl.innerHTML = '\u003Cstrong>sendBeacon mode:\u003C\u002Fstrong> When you click \"Navigate away\", the queue is flushed with \u003Ccode>navigator.sendBeacon(\\'\u002Fanalytics\u002Fbatch\\', blob)\u003C\u002Fcode>. The browser queues the POST and delivers it even as the page is torn down. The return value (\u003Ccode>true\u003C\u002Fcode>) confirms it was accepted.';\n      code.innerHTML = `\u003Cspan class=\"cm\">\u002F\u002F visibilitychange + sendBeacon pattern\u003C\u002Fspan>\n\u003Cspan class=\"kw\">const\u003C\u002Fspan> eventQueue = [];\n\n\u003Cspan class=\"fn\">document\u003C\u002Fspan>.\u003Cspan class=\"fn\">addEventListener\u003C\u002Fspan>(\u003Cspan class=\"str\">'visibilitychange'\u003C\u002Fspan>, () => {\n  \u003Cspan class=\"kw\">if\u003C\u002Fspan> (\u003Cspan class=\"fn\">document\u003C\u002Fspan>.visibilityState === \u003Cspan class=\"str\">'hidden'\u003C\u002Fspan>) {\n    \u003Cspan class=\"kw\">const\u003C\u002Fspan> body = \u003Cspan class=\"kw\">new\u003C\u002Fspan> \u003Cspan class=\"fn\">Blob\u003C\u002Fspan>(\n      [\u003Cspan class=\"fn\">JSON\u003C\u002Fspan>.stringify(eventQueue)],\n      { type: \u003Cspan class=\"str\">'application\u002Fjson'\u003C\u002Fspan> }\n    );\n    navigator.\u003Cspan class=\"fn\">sendBeacon\u003C\u002Fspan>(\u003Cspan class=\"str\">'\u002Fanalytics\u002Fbatch'\u003C\u002Fspan>, body);\n  }\n});`;\n    } else {\n      expl.innerHTML = '\u003Cstrong>fetch mode:\u003C\u002Fstrong> When you click \"Navigate away\", the queue is flushed with a plain \u003Ccode>fetch()\u003C\u002Fcode> in a \u003Ccode>beforeunload\u003C\u002Fcode> handler. The browser starts the request — but tears down the page context concurrently. \u003Cem>The request is often cancelled before it completes.\u003C\u002Fem>';\n      code.innerHTML = `\u003Cspan class=\"cm\">\u002F\u002F ⚠️ Unreliable: fetch in beforeunload\u003C\u002Fspan>\n\u003Cspan class=\"kw\">const\u003C\u002Fspan> eventQueue = [];\n\nwindow.\u003Cspan class=\"fn\">addEventListener\u003C\u002Fspan>(\u003Cspan class=\"str\">'beforeunload'\u003C\u002Fspan>, () => {\n  \u003Cspan class=\"cm\">\u002F\u002F The browser may cancel this before it sends\u003C\u002Fspan>\n  \u003Cspan class=\"fn\">fetch\u003C\u002Fspan>(\u003Cspan class=\"str\">'\u002Fanalytics\u002Fbatch'\u003C\u002Fspan>, {\n    method: \u003Cspan class=\"str\">'POST'\u003C\u002Fspan>,\n    body: \u003Cspan class=\"fn\">JSON\u003C\u002Fspan>.stringify(eventQueue),\n  });\n});`;\n    }\n  }\n\n  function addEvent(type) {\n    eventCounts[type]++;\n    document.getElementById('cnt-' + type).textContent = eventCounts[type];\n\n    const entry = { event: labels[type], ts: ts(), t: Date.now() - sessionStart };\n    eventQueue.push(entry);\n\n    const log = document.getElementById('queue-log');\n    if (log.querySelector('.empty, [style*=\"italic\"]')) log.innerHTML = '';\n    const div = document.createElement('div');\n    div.className = 'queue-entry';\n    div.innerHTML = `\u003Cspan class=\"ts\">${entry.ts}\u003C\u002Fspan>\u003Cspan class=\"ev\">${entry.event}\u003C\u002Fspan>`;\n    log.appendChild(div);\n    log.scrollTop = log.scrollHeight;\n\n    document.getElementById('queue-size').textContent = eventQueue.length;\n    document.getElementById('exit-btn').disabled = false;\n  }\n\n  function simulateExit() {\n    const netLog = document.getElementById('net-log');\n    if (netLog.querySelector('[style*=\"italic\"]')) netLog.innerHTML = '';\n\n    const count = eventQueue.length;\n    const bytes = JSON.stringify(eventQueue).length;\n\n    if (mode === 'beacon') {\n      \u002F\u002F Simulate sendBeacon — always succeeds (returns true)\n      const accepted = true; \u002F\u002F In a real page: navigator.sendBeacon(url, blob)\n\n      addNetEntry(netLog, 'queued', `POST \u002Fanalytics\u002Fbatch`, `${count} events · ${bytes} B · sendBeacon queued (returned ${accepted})`);\n\n      setTimeout(() => {\n        addNetEntry(netLog, 'sent', `✓ Delivered`, `${count} event(s) flushed — browser guaranteed delivery even after unload`);\n      }, 600);\n\n    } else {\n      \u002F\u002F Simulate fetch in beforeunload — often cancelled\n      addNetEntry(netLog, 'queued', `POST \u002Fanalytics\u002Fbatch`, `${count} events · ${bytes} B · fetch started in beforeunload`);\n\n      \u002F\u002F ~70% chance of cancellation to illustrate the problem\n      const cancelled = Math.random() \u003C 0.7;\n      setTimeout(() => {\n        if (cancelled) {\n          addNetEntry(netLog, 'cancelled', `✗ Request cancelled`, `Page context destroyed before fetch completed — ${count} event(s) lost`);\n        } else {\n          addNetEntry(netLog, 'sent', `✓ Delivered (lucky)`, `Completed this time — but behaviour is browser-specific and unreliable`);\n        }\n      }, 500 + Math.random() * 400);\n    }\n\n    \u002F\u002F Reset queue\n    eventQueue = [];\n    document.getElementById('queue-log').innerHTML = '\u003Cspan style=\"color:var(--faint);font-style:italic\">Queue cleared — start a new session\u003C\u002Fspan>';\n    document.getElementById('queue-size').textContent = '0';\n    document.getElementById('exit-btn').disabled = true;\n  }\n\n  function addNetEntry(log, type, msg, sub) {\n    const div = document.createElement('div');\n    div.className = 'net-entry';\n    const badgeClass = type === 'sent' ? 'badge-sent' : type === 'cancelled' ? 'badge-cancelled' : 'badge-queued';\n    const badgeLabel = type === 'sent' ? '200 OK' : type === 'cancelled' ? 'CANCELLED' : 'QUEUED';\n    div.innerHTML = `\u003Cspan class=\"badge ${badgeClass}\">${badgeLabel}\u003C\u002Fspan>\u003Cspan class=\"net-msg\">${msg}\u003C\u002Fspan>\u003Cspan class=\"net-sub\">${sub}\u003C\u002Fspan>`;\n    log.appendChild(div);\n    log.scrollTop = log.scrollHeight;\n  }\n\n  function resetAll() {\n    eventQueue = [];\n    eventCounts = { page_view: 0, click: 0, scroll_depth: 0, search: 0 };\n    sessionStart = Date.now();\n    Object.keys(eventCounts).forEach(k => {\n      document.getElementById('cnt-' + k).textContent = '0';\n    });\n    document.getElementById('queue-log').innerHTML = '\u003Cspan style=\"color:var(--faint);font-style:italic\">Queue is empty — trigger some events\u003C\u002Fspan>';\n    document.getElementById('net-log').innerHTML = '\u003Cspan style=\"color:var(--faint);font-style:italic\">Delivery log appears here after navigating away\u003C\u002Fspan>';\n    document.getElementById('queue-size').textContent = '0';\n    document.getElementById('exit-btn').disabled = true;\n  }",{"height":52,"autorun":17},520,{"slug":45,"title":54,"excerpt":55,"coverUrl":56,"vertical":57},"Your fetch in beforeunload is silently killed. navigator.sendBeacon guarantees delivery.","When the page unloads, the browser may cancel any in-flight fetch or XHR before it completes. navigator.sendBeacon sends a POST the browser commits to delivering, even after the document is gone.","\u002Fmedia\u002Fcovers\u002Fnavigator-sendbeacon-reliable-analytics.png",{"slug":6},[59,63,67,71,75,79,83,87,91,95,98,101],{"slug":60,"name":61,"articles":62},"webdev","Webdev",61,{"slug":64,"name":65,"articles":66},"frontend","Frontend",55,{"slug":68,"name":69,"articles":70},"javascript","Javascript",52,{"slug":72,"name":73,"articles":74},"css","Css",23,{"slug":76,"name":77,"articles":78},"typescript","Typescript",10,{"slug":80,"name":81,"articles":82},"performance","Performance",9,{"slug":84,"name":85,"articles":86},"grammar","Grammar",6,{"slug":88,"name":89,"articles":90},"react","React",5,{"slug":92,"name":93,"articles":94},"html","Html",4,{"slug":96,"name":97,"articles":94},"tutorial","Tutorial",{"slug":99,"name":100,"articles":94},"node","Node",{"slug":102,"name":103,"articles":43},"ai","Ai"]