[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"verticals":3,"playground-broadcast-channel-cross-tab-messaging":32},[4,20],{"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","Build. Learn. Ship.","Practical courses, engineering-grade articles and open-source tools for people who ship.","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.","Structured paths, listening drills and spaced repetition that actually sticks.","amber-400","⌘",[13,15,29],"es",{"courses":17,"paths":17,"articles":18,"exams":18,"flashcards":18,"packages":18,"community":17,"certificates":18,"teams":18,"commerce":17},2,{"slug":33,"title":34,"summary":35,"html":36,"css":37,"js":38,"config":39,"doc":41},"broadcast-channel-cross-tab-messaging","BroadcastChannel — interactive playground",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">📡 BroadcastChannel live\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      Two simulated browser tabs — both subscribed to the same\n      \u003Ccode>BroadcastChannel('demo')\u003C\u002Fcode>. Type a message in Tab A and watch it\n      arrive in Tab B in real time. The sender never receives its own message.\n    \u003C\u002Fp>\n\n    \u003C!-- Panel 1: live cross-tab demo -->\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> Send a message between tabs\u003C\u002Fdiv>\n      \u003Cdiv class=\"tabs-wrapper\">\n        \u003C!-- Tab A (sender) -->\n        \u003Cdiv class=\"tab-sim\">\n          \u003Cdiv class=\"tab-bar\">\n            \u003Cdiv class=\"tab-dot red\">\u003C\u002Fdiv>\n            \u003Cdiv class=\"tab-dot amber\">\u003C\u002Fdiv>\n            \u003Cdiv class=\"tab-dot green\">\u003C\u002Fdiv>\n            \u003Cspan class=\"tab-title\">Tab A — sender\u003C\u002Fspan>\n          \u003C\u002Fdiv>\n          \u003Cdiv class=\"tab-body\">\n            \u003Cdiv class=\"label\" style=\"margin-bottom:6px\">Message to broadcast\u003C\u002Fdiv>\n            \u003Cdiv class=\"send-row\">\n              \u003Cinput type=\"text\" id=\"msgInput\" placeholder=\"e.g. LOGOUT or cart updated\" maxlength=\"80\" \u002F>\n              \u003Cbutton class=\"btn primary sm\" id=\"sendBtn\">Send\u003C\u002Fbutton>\n            \u003C\u002Fdiv>\n            \u003Cdiv style=\"margin-top:10px\">\n              \u003Cdiv class=\"label\" style=\"margin-bottom:4px\">Quick scenarios\u003C\u002Fdiv>\n              \u003Cdiv class=\"btn-row\" style=\"flex-wrap:wrap;gap:6px\">\n                \u003Cbutton class=\"btn sm\" data-preset='{\"type\":\"LOGOUT\"}'>Logout\u003C\u002Fbutton>\n                \u003Cbutton class=\"btn sm\" data-preset='{\"type\":\"CART_UPDATED\",\"count\":3}'>Cart +1\u003C\u002Fbutton>\n                \u003Cbutton class=\"btn sm\" data-preset='{\"type\":\"THEME_CHANGED\",\"theme\":\"dark\"}'>Dark mode\u003C\u002Fbutton>\n                \u003Cbutton class=\"btn sm\" data-preset='{\"type\":\"NOTIFICATION\",\"text\":\"New message\"}'>Notify\u003C\u002Fbutton>\n              \u003C\u002Fdiv>\n            \u003C\u002Fdiv>\n            \u003Cdiv id=\"sentBadge\" class=\"event-badge none\" style=\"margin-top:10px\">no messages sent yet\u003C\u002Fdiv>\n          \u003C\u002Fdiv>\n        \u003C\u002Fdiv>\n\n        \u003C!-- Tab B (receiver) -->\n        \u003Cdiv class=\"tab-sim\">\n          \u003Cdiv class=\"tab-bar\">\n            \u003Cdiv class=\"tab-dot red\">\u003C\u002Fdiv>\n            \u003Cdiv class=\"tab-dot amber\">\u003C\u002Fdiv>\n            \u003Cdiv class=\"tab-dot green\">\u003C\u002Fdiv>\n            \u003Cspan class=\"tab-title\">Tab B — receiver\u003C\u002Fspan>\n          \u003C\u002Fdiv>\n          \u003Cdiv class=\"tab-body\">\n            \u003Cdiv class=\"label\" style=\"margin-bottom:6px\">Received messages\u003C\u002Fdiv>\n            \u003Cdiv class=\"msg-log\" id=\"msgLog\">\n              \u003Cdiv class=\"empty\">Waiting for messages from Tab A…\u003C\u002Fdiv>\n            \u003C\u002Fdiv>\n            \u003Cp class=\"hint\" style=\"margin-top:8px\">\n              Tab B called\n              \u003Ccode>channel.onmessage = (e) => …\u003C\u002Fcode> — it gets every message\n              Tab A sends.\n            \u003C\u002Fp>\n          \u003C\u002Fdiv>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003C!-- Panel 2: code snippet -->\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> The code behind this demo\u003C\u002Fdiv>\n      \u003Cdiv class=\"code\">\u002F\u002F Tab A — open a channel and send\nconst channel = new BroadcastChannel('demo');\nchannel.postMessage({ type: 'LOGOUT' });\n\n\u002F\u002F Tab B — same channel name, receives all messages\nconst channel = new BroadcastChannel('demo');\nchannel.onmessage = (event) => {\n  console.log(event.data); \u002F\u002F { type: 'LOGOUT' }\n};\n\n\u002F\u002F Clean up when done\nchannel.close();\u003C\u002Fdiv>\n      \u003Cp class=\"hint\" style=\"margin-top:10px\">\n        Any tab, worker, or iframe on the same origin that opens a channel with the\n        same name is part of the group. The sender never receives its own messages.\n      \u003C\u002Fp>\n    \u003C\u002Fdiv>\n\n    \u003C!-- Panel 3: BroadcastChannel vs localStorage -->\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">3\u003C\u002Fspan> BroadcastChannel vs the localStorage trick\u003C\u002Fdiv>\n      \u003Ctable class=\"vs-table\">\n        \u003Cthead>\n          \u003Ctr>\n            \u003Cth>Aspect\u003C\u002Fth>\n            \u003Cth>localStorage + storage event\u003C\u002Fth>\n            \u003Cth>BroadcastChannel\u003C\u002Fth>\n          \u003C\u002Ftr>\n        \u003C\u002Fthead>\n        \u003Ctbody>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Sending\u003C\u002Ftd>\n            \u003Ctd>\u003Ccode>localStorage.setItem(key, JSON.stringify(data))\u003C\u002Fcode>\u003C\u002Ftd>\n            \u003Ctd>\u003Ccode>channel.postMessage(data)\u003C\u002Fcode>\u003C\u002Ftd>\n          \u003C\u002Ftr>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Serialization\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">Manual — must \u003Ccode>JSON.stringify\u003C\u002Fcode> and \u003Ccode>JSON.parse\u003C\u002Fcode>\u003C\u002Ftd>\n            \u003Ctd class=\"good\">None — structured clone handles it\u003C\u002Ftd>\n          \u003C\u002Ftr>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Cleanup\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">Must \u003Ccode>removeItem\u003C\u002Fcode> immediately (triggers a second event)\u003C\u002Ftd>\n            \u003Ctd class=\"good\">No side effects — just send\u003C\u002Ftd>\n          \u003C\u002Ftr>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Event filtering\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">Must check \u003Ccode>event.key\u003C\u002Fcode> and \u003Ccode>event.newValue\u003C\u002Fcode>\u003C\u002Ftd>\n            \u003Ctd class=\"good\">Only receives messages from the same channel name\u003C\u002Ftd>\n          \u003C\u002Ftr>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Data types\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">Strings only\u003C\u002Ftd>\n            \u003Ctd class=\"good\">Any structured-cloneable value (objects, arrays, Date, Map…)\u003C\u002Ftd>\n          \u003C\u002Ftr>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Same-tab detection\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">Sender receives its own events — must add a timestamp filter\u003C\u002Ftd>\n            \u003Ctd class=\"good\">Sender never receives its own messages\u003C\u002Ftd>\n          \u003C\u002Ftr>\n        \u003C\u002Ftbody>\n      \u003C\u002Ftable>\n    \u003C\u002Fdiv>\n\n    \u003C!-- Panel 4: What you can send -->\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">4\u003C\u002Fspan> What you can send (structured clone)\u003C\u002Fdiv>\n      \u003Cdiv class=\"code\" id=\"cloneDemo\">\u002F\u002F ✅ All of these work with postMessage:\nchannel.postMessage({ type: 'UPDATE', count: 42 });     \u002F\u002F object\nchannel.postMessage([1, 2, 3]);                          \u002F\u002F array\nchannel.postMessage(new Date());                         \u002F\u002F Date\nchannel.postMessage(new Map([['key', 'value']]));        \u002F\u002F Map\nchannel.postMessage(new Set([1, 2, 3]));                 \u002F\u002F Set\n\n\u002F\u002F ❌ These throw a DataCloneError:\nchannel.postMessage(() => {});          \u002F\u002F functions\nchannel.postMessage(document.body);    \u002F\u002F DOM nodes\u003C\u002Fdiv>\n    \u003C\u002Fdiv>\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.tabs-wrapper {\n    display: grid;\n    grid-template-columns: 1fr 1fr;\n    gap: 12px;\n  }\n  @media (max-width: 540px) {\n    .tabs-wrapper { grid-template-columns: 1fr; }\n  }\n\n  .tab-sim {\n    background: var(--panel-2);\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    overflow: hidden;\n  }\n  .tab-bar {\n    display: flex;\n    align-items: center;\n    gap: 8px;\n    padding: 8px 12px;\n    background: var(--panel-3, color-mix(in srgb, var(--ink) 6%, var(--bg)));\n    border-bottom: 1px solid var(--line);\n  }\n  .tab-dot {\n    width: 11px; height: 11px;\n    border-radius: 50%;\n  }\n  .tab-dot.red   { background: #f87171; }\n  .tab-dot.amber { background: #fbbf24; }\n  .tab-dot.green { background: #4ade80; }\n  .tab-title {\n    font-size: 0.75rem;\n    font-weight: 700;\n    color: var(--muted);\n    margin-left: 4px;\n    letter-spacing: 0.04em;\n  }\n  .tab-body { padding: 14px; }\n\n  .msg-log {\n    min-height: 140px;\n    max-height: 200px;\n    overflow-y: auto;\n    background: var(--bg);\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    padding: 8px 10px;\n    font-family: var(--mono);\n    font-size: 0.78rem;\n    line-height: 1.7;\n  }\n  .msg-log .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 0.25s ease;\n  }\n  .msg-log .entry:last-child { border-bottom: none; }\n  @keyframes fadein { from { opacity: 0; transform: translateY(4px); } to { opacity: 1; } }\n  .msg-log .ts { color: var(--faint); min-width: 6ch; }\n  .msg-log .data { color: var(--accent); word-break: break-all; }\n  .msg-log .empty { color: var(--faint); font-style: italic; }\n\n  .send-row {\n    display: flex;\n    gap: 8px;\n    margin-top: 10px;\n  }\n  .send-row input {\n    flex: 1;\n    font-family: var(--mono);\n    font-size: 0.85rem;\n  }\n\n  .event-badge {\n    display: inline-flex;\n    align-items: center;\n    gap: 5px;\n    font-size: 0.7rem;\n    font-weight: 700;\n    padding: 2px 8px;\n    border-radius: 20px;\n    margin-top: 6px;\n  }\n  .event-badge.sent { color: var(--good); background: color-mix(in srgb, var(--good) 14%, transparent); }\n  .event-badge.none { color: var(--faint); background: color-mix(in srgb, var(--faint) 10%, transparent); }\n\n  .vs-table {\n    width: 100%;\n    border-collapse: collapse;\n    font-size: 0.8rem;\n  }\n  .vs-table th {\n    font-size: 0.7rem;\n    text-transform: uppercase;\n    letter-spacing: 0.06em;\n    font-weight: 800;\n    color: var(--muted);\n    padding: 6px 10px;\n    text-align: left;\n    border-bottom: 1px solid var(--line);\n  }\n  .vs-table td {\n    padding: 7px 10px;\n    border-bottom: 1px solid var(--line-soft);\n    vertical-align: top;\n    line-height: 1.5;\n    color: var(--ink);\n  }\n  .vs-table tr:last-child td { border-bottom: none; }\n  .vs-table .row-label { color: var(--muted); font-weight: 600; min-width: 8ch; }\n  .vs-table .good { color: var(--good); }\n  .vs-table .bad  { color: var(--bad); }\n  .vs-table code { font-family: var(--mono); font-size: 0.8em; background: var(--panel-2); padding: 1px 4px; border-radius: 3px; }","\u002F\u002F Two BroadcastChannel instances with the same name on the same page.\n    \u002F\u002F When senderChannel posts, receiverChannel's onmessage fires —\n    \u002F\u002F demonstrating real cross-context delivery without needing two literal tabs.\n    const senderChannel   = new BroadcastChannel('demo');\n    const receiverChannel = new BroadcastChannel('demo');\n\n    const msgInput  = document.getElementById('msgInput');\n    const sendBtn   = document.getElementById('sendBtn');\n    const msgLog    = document.getElementById('msgLog');\n    const sentBadge = document.getElementById('sentBadge');\n\n    let sendCount = 0;\n\n    function timestamp() {\n      const d = new Date();\n      return d.toLocaleTimeString('en', { hour12: false, hour: '2-digit', minute: '2-digit', second: '2-digit' });\n    }\n\n    function logMessage(data) {\n      const wasEmpty = msgLog.querySelector('.empty');\n      if (wasEmpty) wasEmpty.remove();\n\n      const entry = document.createElement('div');\n      entry.className = 'entry';\n      entry.innerHTML = `\n        \u003Cspan class=\"ts\">${timestamp()}\u003C\u002Fspan>\n        \u003Cspan class=\"data\">${escapeHtml(JSON.stringify(data))}\u003C\u002Fspan>\n      `;\n      msgLog.appendChild(entry);\n      msgLog.scrollTop = msgLog.scrollHeight;\n    }\n\n    function escapeHtml(str) {\n      return str.replace(\u002F&\u002Fg, '&').replace(\u002F\u003C\u002Fg, '<').replace(\u002F>\u002Fg, '>');\n    }\n\n    function send(payload) {\n      senderChannel.postMessage(payload);\n      sendCount++;\n      sentBadge.textContent = `✓ ${sendCount} message${sendCount === 1 ? '' : 's'} sent`;\n      sentBadge.className = 'event-badge sent';\n    }\n\n    sendBtn.addEventListener('click', () => {\n      const raw = msgInput.value.trim();\n      if (!raw) return;\n      let payload;\n      try {\n        payload = JSON.parse(raw);\n      } catch {\n        payload = { type: raw };\n      }\n      send(payload);\n      msgInput.value = '';\n    });\n\n    msgInput.addEventListener('keydown', (e) => {\n      if (e.key === 'Enter') sendBtn.click();\n    });\n\n    document.querySelectorAll('[data-preset]').forEach(btn => {\n      btn.addEventListener('click', () => {\n        try {\n          send(JSON.parse(btn.dataset.preset));\n        } catch {\u002F* ignore *\u002F}\n      });\n    });\n\n    receiverChannel.onmessage = (event) => {\n      logMessage(event.data);\n    };\n\n    window.addEventListener('beforeunload', () => {\n      senderChannel.close();\n      receiverChannel.close();\n    });",{"height":40,"autorun":17},520,{"slug":33,"title":42,"excerpt":43,"coverUrl":44},"Stop using the localStorage hack to sync browser tabs. BroadcastChannel does it natively.","Syncing state across browser tabs with localStorage events is a widely-used trick that requires JSON.stringify, event filtering, and careful cleanup. The Broadcast Channel API delivers messages between tabs directly, with none of the side effects.","\u002Fmedia\u002Fcovers\u002Fbroadcast-channel-cross-tab-messaging.png"]