[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"verticals":3,"playground-resize-observer-element-size":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},"resize-observer-element-size","ResizeObserver — interactive playground",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">🎮 ResizeObserver — watch the element, not the window\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      Drag the box's bottom-right corner, or move the slider — either way a \u003Ccode>ResizeObserver\u003C\u002Fcode>\n      reports the box's own size live, and the layout inside reacts to \u003Cstrong>its\u003C\u002Fstrong> width, not your\n      browser window's.\n    \u003C\u002Fp>\n\n    \u003Cdiv class=\"banner\" id=\"unsupportedBanner\">\n      Your browser doesn't support \u003Ccode>ResizeObserver\u003C\u002Fcode>. Try a recent Chrome, Firefox, Safari, or\n      Edge — it's been Baseline since 2020.\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> Resize the box\u003C\u002Fdiv>\n\n      \u003Cdiv class=\"resize-wrap\">\n        \u003Cdiv class=\"resize-box\" id=\"box\">\n          \u003Cdiv class=\"mini-cards\" id=\"miniCards\">\n            \u003Cdiv class=\"mini-card\">📄 Card A\u003C\u002Fdiv>\n            \u003Cdiv class=\"mini-card\">📄 Card B\u003C\u002Fdiv>\n            \u003Cdiv class=\"mini-card\">📄 Card C\u003C\u002Fdiv>\n          \u003C\u002Fdiv>\n          \u003Cdiv class=\"box-tag\" id=\"boxTag\" aria-live=\"polite\">⏳ measuring…\u003C\u002Fdiv>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"wrap-controls\" style=\"margin-top: 14px\">\n        \u003Cdiv class=\"field grow\">\n          \u003Cspan class=\"ctl-label\" id=\"widthLabel\">Width — \u003Cspan id=\"widthVal\">340\u003C\u002Fspan>px\u003C\u002Fspan>\n          \u003Cinput\n            type=\"range\"\n            id=\"widthSlider\"\n            min=\"160\"\n            max=\"680\"\n            step=\"10\"\n            value=\"340\"\n            aria-labelledby=\"widthLabel\"\n          \u002F>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"presets\" style=\"margin-top: 12px\">\n        \u003Cbutton class=\"btn sm\" data-w=\"200\" data-h=\"120\">Snap: small\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-w=\"420\" data-h=\"180\">Snap: medium\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-w=\"640\" data-h=\"220\">Snap: large\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn ghost sm\" id=\"resetBtn\">Reset\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n\n      \u003Cp class=\"hint\">\n        The corner-drag is mouse\u002Ftouch only — the slider is the accessible equivalent, and both do the\n        exact same thing: change the element's own box. Watch the cards inside flip from stacked to\n        side-by-side once the box gets wide enough — that's an element-driven breakpoint, the same trick\n        behind CSS container queries, done in JavaScript.\n      \u003C\u002Fp>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> Live ResizeObserver readout\u003C\u002Fdiv>\n\n      \u003Cdiv class=\"counters\">\n        \u003Cspan class=\"pill\" id=\"cbPill\">callback fired: \u003Cstrong id=\"cbCount\">0\u003C\u002Fstrong>×\u003C\u002Fspan>\n        \u003Cspan class=\"pill\" id=\"winPill\">window \"resize\" events: \u003Cstrong id=\"winCount\">0\u003C\u002Fstrong>×\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n\n      \u003Cpre class=\"code\" id=\"entryCode\">\u002F\u002F resize the box above — the entry appears here\u003C\u002Fpre>\n\n      \u003Cp class=\"hint\">\n        \u003Ccode>contentRect\u003C\u002Fcode>, \u003Ccode>contentBoxSize\u003C\u002Fcode>, and \u003Ccode>borderBoxSize\u003C\u002Fcode> are the three\n        ways one \u003Ccode>ResizeObserverEntry\u003C\u002Fcode> reports the new size. Drag or slide the box and this\n        updates instantly; resize your actual browser window instead and it doesn't move — only the\n        \"window resize events\" counter above does. That's the whole point: the observer reacts to the\n        \u003Cstrong>element\u003C\u002Fstrong>, independent of the window.\n      \u003C\u002Fp>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">3\u003C\u002Fspan> Entry log\u003C\u002Fdiv>\n      \u003Cdiv class=\"log-head\">\n        \u003Cp class=\"hint\">Every batch the browser delivers, newest first.\u003C\u002Fp>\n        \u003Cbutton class=\"btn ghost sm\" id=\"clearLog\">Clear\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"log\" id=\"log\" data-empty=\"1\" aria-live=\"polite\">\n        Observing… the box's starting size will appear here in a moment.\n      \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\u002F* Demo-specific CSS ONLY — base.css owns tokens, layout, panels, buttons,\n     toggles, sliders, code blocks, status\u002Flog, banners, presets, pills. *\u002F\n\n  .resize-wrap {\n    display: flex;\n    justify-content: center;\n    padding: 4px 0 2px;\n  }\n\n  \u002F* The element the reader resizes. resize: both + overflow: auto is what\n     gives it the native drag handle in the bottom-right corner; the width\n     slider below is the keyboard-accessible equivalent. *\u002F\n  .resize-box {\n    width: 340px;\n    height: 160px;\n    min-width: 140px;\n    min-height: 90px;\n    max-width: 100%;\n    max-height: 360px;\n    resize: both;\n    overflow: auto;\n    border: 2px solid var(--accent);\n    border-radius: var(--radius-sm);\n    background: var(--panel-2);\n    padding: 14px;\n    transition: width 0.22s ease, height 0.22s ease;\n    box-shadow: var(--shadow-sm);\n  }\n\n  \u002F* A tiny \"card list\" inside the box that reflows at the box's OWN width\n     breakpoints — the container-query-by-JS pattern the post describes. *\u002F\n  .mini-cards {\n    display: flex;\n    flex-direction: column;\n    gap: 6px;\n    width: 100%;\n    margin-bottom: 10px;\n  }\n  .mini-cards.wide {\n    flex-direction: row;\n  }\n  .mini-card {\n    background: var(--card);\n    border: 1px solid var(--line);\n    border-radius: 8px;\n    padding: 6px 10px;\n    font-size: 0.78rem;\n    font-weight: 700;\n    white-space: nowrap;\n    overflow: hidden;\n    text-overflow: ellipsis;\n  }\n  .mini-cards.wide .mini-card {\n    flex: 1;\n    text-align: center;\n  }\n\n  .box-tag {\n    font-size: 0.82rem;\n    font-weight: 800;\n    color: var(--muted);\n  }\n\n  .counters {\n    display: flex;\n    flex-wrap: wrap;\n    gap: 10px;\n    margin-bottom: 12px;\n  }\n\n  .log-head {\n    display: flex;\n    align-items: center;\n    justify-content: space-between;\n    gap: 10px;\n    margin-bottom: 8px;\n  }\n  .log-head .hint {\n    margin: 0;\n  }","\"use strict\";\n  const $ = (id) => document.getElementById(id);\n\n  const box = $(\"box\");\n  const miniCards = $(\"miniCards\");\n  const boxTag = $(\"boxTag\");\n  const widthSlider = $(\"widthSlider\");\n  const widthVal = $(\"widthVal\");\n  const cbCountEl = $(\"cbCount\");\n  const winCountEl = $(\"winCount\");\n  const entryCode = $(\"entryCode\");\n  const log = $(\"log\");\n\n  const DEFAULT_W = 340;\n  const DEFAULT_H = 160;\n  const COMPACT_MAX = 260; \u002F\u002F below this: compact, stacked\n  const WIDE_MIN = 460; \u002F\u002F at\u002Fabove this: wide, side-by-side\n\n  let callbacks = 0;\n  let winEvents = 0;\n  const startTime = performance.now();\n\n  const round = (n) => Math.round(n);\n\n  function setBreakpoint(width) {\n    const wide = width >= WIDE_MIN;\n    miniCards.classList.toggle(\"wide\", wide);\n    if (width \u003C COMPACT_MAX) {\n      boxTag.textContent = \"🔹 compact — stacked\";\n    } else if (width \u003C WIDE_MIN) {\n      boxTag.textContent = \"◼ regular — stacked\";\n    } else {\n      boxTag.textContent = \"⬛ wide — side-by-side\";\n    }\n  }\n\n  function renderEntry(entry) {\n    const { width, height } = entry.contentRect;\n    const content = entry.contentBoxSize ? entry.contentBoxSize[0] : null;\n    const border = entry.borderBoxSize ? entry.borderBoxSize[0] : null;\n\n    let code =\n      `\u003Cspan class=\"tok-prop\">entry.contentRect\u003C\u002Fspan>        → ` +\n      `{ width: \u003Cspan class=\"tok-num\">${round(width)}\u003C\u002Fspan>, height: \u003Cspan class=\"tok-num\">${round(height)}\u003C\u002Fspan> }`;\n    if (content) {\n      code +=\n        `\\n\u003Cspan class=\"tok-prop\">entry.contentBoxSize[0]\u003C\u002Fspan>  → ` +\n        `{ inlineSize: \u003Cspan class=\"tok-num\">${round(content.inlineSize)}\u003C\u002Fspan>, blockSize: \u003Cspan class=\"tok-num\">${round(content.blockSize)}\u003C\u002Fspan> }`;\n    }\n    if (border) {\n      code +=\n        `\\n\u003Cspan class=\"tok-prop\">entry.borderBoxSize[0]\u003C\u002Fspan>   → ` +\n        `{ inlineSize: \u003Cspan class=\"tok-num\">${round(border.inlineSize)}\u003C\u002Fspan>, blockSize: \u003Cspan class=\"tok-num\">${round(border.blockSize)}\u003C\u002Fspan> }`;\n    }\n    entryCode.innerHTML = code;\n\n    const elapsed = ((performance.now() - startTime) \u002F 1000).toFixed(2);\n    let line = `+${elapsed}s  #${callbacks}  content ${round(width)}×${round(height)}`;\n    if (border) line += `  border ${round(border.inlineSize)}×${round(border.blockSize)}`;\n\n    if (log.dataset.empty === \"1\") {\n      log.textContent = \"\";\n      log.dataset.empty = \"0\";\n    }\n    const lines = (line + \"\\n\" + log.textContent).split(\"\\n\").filter(Boolean);\n    log.textContent = lines.slice(0, 40).join(\"\\n\");\n  }\n\n  \u002F\u002F The concept: watch the ELEMENT, not the window. This callback fires once\n  \u002F\u002F as soon as observation starts (the box's current size, not a \"change\"),\n  \u002F\u002F and again on every subsequent size change — drag, slider, preset, or\n  \u002F\u002F anything else that changes the box's own layout.\n  const ro = new ResizeObserver((entries) => {\n    callbacks++;\n    cbCountEl.textContent = callbacks;\n    for (const entry of entries) {\n      const w = entry.contentBoxSize ? entry.contentBoxSize[0].inlineSize : entry.contentRect.width;\n      setBreakpoint(w);\n      renderEntry(entry);\n    }\n  });\n\n  if (\"ResizeObserver\" in window) {\n    ro.observe(box);\n  } else {\n    $(\"unsupportedBanner\").classList.add(\"show\");\n  }\n\n  \u002F\u002F Contrast: this only increments when the actual browser window\u002Fviewport\n  \u002F\u002F resizes — dragging or sliding the box above never touches it.\n  window.addEventListener(\"resize\", () => {\n    winEvents++;\n    winCountEl.textContent = winEvents;\n  });\n\n  widthSlider.addEventListener(\"input\", () => {\n    const w = Number(widthSlider.value);\n    widthVal.textContent = w;\n    box.style.width = w + \"px\";\n  });\n\n  document.querySelectorAll(\"[data-w]\").forEach((btn) => {\n    btn.addEventListener(\"click\", () => {\n      const w = Number(btn.dataset.w);\n      const h = Number(btn.dataset.h);\n      box.style.width = w + \"px\";\n      box.style.height = h + \"px\";\n      widthSlider.value = w;\n      widthVal.textContent = w;\n    });\n  });\n\n  $(\"resetBtn\").addEventListener(\"click\", () => {\n    box.style.width = DEFAULT_W + \"px\";\n    box.style.height = DEFAULT_H + \"px\";\n    widthSlider.value = DEFAULT_W;\n    widthVal.textContent = DEFAULT_W;\n  });\n\n  $(\"clearLog\").addEventListener(\"click\", () => {\n    log.textContent = \"Cleared — resize the box to generate new entries.\";\n    log.dataset.empty = \"1\";\n  });",{"height":40,"autorun":17},520,{"slug":33,"title":42,"excerpt":43,"coverUrl":44},"You're watching `window` to detect element size changes. `ResizeObserver` watches the element itself.","A `window` resize listener only fires when the viewport changes. ResizeObserver fires whenever the element's own box changes — from content loading, parent reflow, container queries, or anything else.","\u002Fmedia\u002Fcovers\u002Fresize-observer-element-size.png"]