[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"playground-mutation-observer-dom-change-detection":3,"verticals":17},{"slug":4,"title":5,"summary":6,"html":7,"css":8,"js":9,"config":10,"doc":13},"mutation-observer-dom-change-detection","MutationObserver — interactive playground",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">👁️ MutationObserver live\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      A single \u003Ccode>MutationObserver\u003C\u002Fcode> watches the target element below\n      for every type of mutation. Use the controls to trigger changes — each one\n      fires the observer and appears in the log with its full \u003Ccode>MutationRecord\u003C\u002Fcode>.\n    \u003C\u002Fp>\n\n    \u003C!-- Panel 1: the observed target -->\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> Observed target element\u003C\u002Fdiv>\n      \u003Cdiv class=\"label\" style=\"margin-bottom:6px\">\n        This element is being watched with\n        \u003Ccode>{ childList: true, attributes: true, characterData: true, subtree: true }\u003C\u002Fcode>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"demo-target\" id=\"target\">\n        \u003Cspan class=\"child-tag\" data-id=\"1\">child-1 \u003Cbutton onclick=\"removeChild('1')\">✕\u003C\u002Fbutton>\u003C\u002Fspan>\n        \u003Cspan class=\"child-tag\" data-id=\"2\">child-2 \u003Cbutton onclick=\"removeChild('2')\">✕\u003C\u002Fbutton>\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"counter-row\">\n        \u003Cspan>Children: \u003Cstrong id=\"childCount\">2\u003C\u002Fstrong>\u003C\u002Fspan>\n        \u003Cspan>data-status: \u003Cstrong id=\"attrDisplay\">none\u003C\u002Fstrong>\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003C!-- Panel 2: controls -->\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> Trigger mutations\u003C\u002Fdiv>\n\n      \u003Cdiv class=\"label\" style=\"margin-bottom:6px\">childList — add or remove a child node\u003C\u002Fdiv>\n      \u003Cdiv class=\"btn-row\">\n        \u003Cbutton class=\"btn primary sm\" onclick=\"addChild()\">+ Add child\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" onclick=\"removeLastChild()\">− Remove last child\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" onclick=\"addManyChildren()\">Add 5 at once (batched)\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"label\" style=\"margin-top:14px; margin-bottom:6px\">attributes — change an attribute on the target\u003C\u002Fdiv>\n      \u003Cdiv class=\"attr-row\">\n        \u003Cinput type=\"text\" id=\"attrVal\" placeholder=\"new data-status value…\" maxlength=\"40\" \u002F>\n        \u003Cbutton class=\"btn primary sm\" onclick=\"changeAttr()\">Set data-status\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" onclick=\"removeAttr()\">Remove attr\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"label\" style=\"margin-top:14px; margin-bottom:6px\">characterData — edit a text node directly\u003C\u002Fdiv>\n      \u003Cdiv class=\"btn-row\">\n        \u003Cbutton class=\"btn primary sm\" onclick=\"changeTextNode()\">Append text node\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" onclick=\"clearTextNodes()\">Clear text nodes\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003C!-- Panel 3: mutation log -->\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\n        \u003Cspan class=\"n\">3\u003C\u002Fspan> MutationRecord log\n        \u003Cbutton class=\"btn sm\" style=\"margin-left:auto;font-size:0.72rem\" onclick=\"clearLog()\">Clear\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"log\" id=\"log\">\n        \u003Cdiv class=\"empty\">No mutations yet — use the controls above…\u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003C!-- Panel 4: the code -->\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">4\u003C\u002Fspan> The code running this demo\u003C\u002Fdiv>\n      \u003Cdiv class=\"code\">const target = document.getElementById('target');\nlet counter = 3;\n\nconst observer = new MutationObserver((mutations) => {\n  for (const mutation of mutations) {\n    \u002F\u002F mutation.type  → 'childList' | 'attributes' | 'characterData'\n    \u002F\u002F mutation.target      → the node that changed\n    \u002F\u002F mutation.addedNodes  → NodeList of added nodes (childList only)\n    \u002F\u002F mutation.oldValue    → previous value (if attributeOldValue\u002F\n    \u002F\u002F                        characterDataOldValue was set)\n    logMutation(mutation);\n  }\n});\n\nobserver.observe(target, {\n  childList: true,\n  subtree: true,\n  attributes: true,\n  characterData: true,\n  attributeOldValue: true,\n  characterDataOldValue: true,\n});\u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003C!-- Panel 5: compare with setInterval -->\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">5\u003C\u002Fspan> Why not just poll?\u003C\u002Fdiv>\n      \u003Ctable class=\"vs-table\">\n        \u003Cthead>\n          \u003Ctr>\n            \u003Cth>Aspect\u003C\u002Fth>\n            \u003Cth class=\"good\">MutationObserver\u003C\u002Fth>\n            \u003Cth class=\"bad\">setInterval polling\u003C\u002Fth>\n          \u003C\u002Ftr>\n        \u003C\u002Fthead>\n        \u003Ctbody>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Timing\u003C\u002Ftd>\n            \u003Ctd class=\"good\">Fires immediately after the change\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">Up to N ms late (interval gap)\u003C\u002Ftd>\n          \u003C\u002Ftr>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">CPU when idle\u003C\u002Ftd>\n            \u003Ctd class=\"good\">Zero — no polling cost\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">Runs every tick regardless\u003C\u002Ftd>\n          \u003C\u002Ftr>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Batching\u003C\u002Ftd>\n            \u003Ctd class=\"good\">Multiple changes → one callback\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">No batching; multiple checks may run\u003C\u002Ftd>\n          \u003C\u002Ftr>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Detail\u003C\u002Ftd>\n            \u003Ctd class=\"good\">Full record: type, target, old value\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">Must diff DOM yourself\u003C\u002Ftd>\n          \u003C\u002Ftr>\n          \u003Ctr>\n            \u003Ctd class=\"row-label\">Cleanup\u003C\u002Ftd>\n            \u003Ctd class=\"good\">\u003Ccode>observer.disconnect()\u003C\u002Fcode>\u003C\u002Ftd>\n            \u003Ctd class=\"bad\">\u003Ccode>clearInterval()\u003C\u002Fcode> (easy to forget)\u003C\u002Ftd>\n          \u003C\u002Ftr>\n        \u003C\u002Ftbody>\n      \u003C\u002Ftable>\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.demo-target {\n    background: var(--panel-2);\n    border: 2px dashed var(--accent);\n    border-radius: var(--radius-sm);\n    min-height: 80px;\n    padding: 12px 14px;\n    font-family: var(--mono);\n    font-size: 0.85rem;\n    color: var(--ink);\n    transition: background 0.2s;\n  }\n  .demo-target.flash {\n    background: color-mix(in srgb, var(--accent) 12%, var(--panel-2));\n  }\n  .demo-target .child-tag {\n    display: inline-flex;\n    align-items: center;\n    gap: 4px;\n    background: var(--panel-3, color-mix(in srgb, var(--ink) 8%, var(--bg)));\n    border: 1px solid var(--line);\n    border-radius: 4px;\n    padding: 3px 10px;\n    margin: 3px;\n    font-size: 0.78rem;\n    color: var(--ink);\n  }\n  .demo-target .child-tag button {\n    background: none;\n    border: none;\n    cursor: pointer;\n    color: var(--bad);\n    font-size: 0.8rem;\n    padding: 0 2px;\n    line-height: 1;\n  }\n\n  .attr-row {\n    display: flex;\n    gap: 8px;\n    flex-wrap: wrap;\n    margin-top: 4px;\n  }\n  .attr-row input[type=\"text\"] {\n    flex: 1;\n    min-width: 100px;\n    font-family: var(--mono);\n    font-size: 0.82rem;\n  }\n\n  .log {\n    min-height: 160px;\n    max-height: 280px;\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: 0.77rem;\n    line-height: 1.8;\n  }\n  .log .entry {\n    padding: 3px 0;\n    border-bottom: 1px solid var(--line-soft);\n    animation: fadein 0.2s ease;\n  }\n  .log .entry:last-child { border-bottom: none; }\n  @keyframes fadein { from { opacity: 0; transform: translateY(3px); } to { opacity: 1; } }\n  .log .empty { color: var(--faint); font-style: italic; }\n  .log .type-badge {\n    display: inline-block;\n    font-size: 0.68rem;\n    font-weight: 800;\n    letter-spacing: 0.04em;\n    padding: 1px 7px;\n    border-radius: 20px;\n    margin-right: 6px;\n    vertical-align: middle;\n  }\n  .log .type-childList { background: color-mix(in srgb, var(--good) 18%, transparent); color: var(--good); }\n  .log .type-attributes { background: color-mix(in srgb, var(--accent) 18%, transparent); color: var(--accent); }\n  .log .type-characterData { background: color-mix(in srgb, var(--warn, #f59e0b) 18%, transparent); color: var(--warn, #f59e0b); }\n  .log .detail { color: var(--muted); }\n  .log .val { color: var(--ink); }\n\n  .counter-row {\n    display: flex;\n    gap: 14px;\n    margin-top: 6px;\n    font-size: 0.78rem;\n    color: var(--muted);\n  }\n  .counter-row strong { color: var(--ink); }\n\n.vs-table { width: 100%; border-collapse: collapse; font-size: 0.8rem; }\n  .vs-table th {\n    font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.06em;\n    font-weight: 800; color: var(--muted); padding: 6px 10px;\n    text-align: left; border-bottom: 1px solid var(--line);\n  }\n  .vs-table td {\n    padding: 7px 10px; border-bottom: 1px solid var(--line-soft);\n    vertical-align: top; line-height: 1.5; 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; }","const target = document.getElementById('target');\n  const log    = document.getElementById('log');\n  let counter  = 3;\n  let textNode = null;\n  let mutationCount = 0;\n\n  const observer = new MutationObserver((mutations) => {\n    flashTarget();\n    for (const m of mutations) {\n      logMutation(m);\n    }\n    updateCounters();\n  });\n\n  observer.observe(target, {\n    childList: true,\n    subtree: true,\n    attributes: true,\n    characterData: true,\n    attributeOldValue: true,\n    characterDataOldValue: true,\n  });\n\n  function flashTarget() {\n    target.classList.add('flash');\n    setTimeout(() => target.classList.remove('flash'), 300);\n  }\n\n  function logMutation(m) {\n    if (log.querySelector('.empty')) log.innerHTML = '';\n    mutationCount++;\n    const entry = document.createElement('div');\n    entry.className = 'entry';\n\n    const badge = document.createElement('span');\n    badge.className = `type-badge type-${m.type}`;\n    badge.textContent = m.type;\n\n    let detail = '';\n    if (m.type === 'childList') {\n      const added   = m.addedNodes.length;\n      const removed = m.removedNodes.length;\n      detail = `added: ${added}, removed: ${removed}`;\n      if (added > 0) detail += ` (${[...m.addedNodes].map(n => n.textContent?.slice(0,20)).join(', ')})`;\n    } else if (m.type === 'attributes') {\n      detail = `${m.attributeName}: \u003Cspan class=\"val\">\"${m.oldValue ?? '∅'}\"\u003C\u002Fspan> → \u003Cspan class=\"val\">\"${m.target.getAttribute(m.attributeName) ?? '∅'}\"\u003C\u002Fspan>`;\n    } else if (m.type === 'characterData') {\n      const from = (m.oldValue ?? '').slice(0, 20);\n      const to   = (m.target.textContent ?? '').slice(0, 20);\n      detail = `text: \u003Cspan class=\"val\">\"${from}\"\u003C\u002Fspan> → \u003Cspan class=\"val\">\"${to}\"\u003C\u002Fspan>`;\n    }\n\n    entry.appendChild(badge);\n    const span = document.createElement('span');\n    span.className = 'detail';\n    span.innerHTML = `#${mutationCount} ${detail}`;\n    entry.appendChild(span);\n\n    log.insertBefore(entry, log.firstChild);\n  }\n\n  function updateCounters() {\n    document.getElementById('childCount').textContent =\n      target.querySelectorAll('.child-tag').length;\n    const attr = target.getAttribute('data-status');\n    document.getElementById('attrDisplay').textContent = attr ?? 'none';\n  }\n\n  function addChild() {\n    const tag = document.createElement('span');\n    tag.className = 'child-tag';\n    tag.dataset.id = counter;\n    const id = counter++;\n    tag.innerHTML = `child-${id} \u003Cbutton onclick=\"removeChild('${id}')\">✕\u003C\u002Fbutton>`;\n    target.appendChild(tag);\n  }\n\n  function removeChild(id) {\n    const el = target.querySelector(`[data-id=\"${id}\"]`);\n    if (el) el.remove();\n    updateCounters();\n  }\n\n  function removeLastChild() {\n    const tags = target.querySelectorAll('.child-tag');\n    if (tags.length) tags[tags.length - 1].remove();\n    updateCounters();\n  }\n\n  function addManyChildren() {\n    \u002F\u002F All 5 additions happen in one synchronous block →\n    \u002F\u002F MutationObserver batches them into ONE callback with 5 addedNodes\n    for (let i = 0; i \u003C 5; i++) {\n      const tag = document.createElement('span');\n      tag.className = 'child-tag';\n      const id = counter++;\n      tag.dataset.id = id;\n      tag.innerHTML = `child-${id} \u003Cbutton onclick=\"removeChild('${id}')\">✕\u003C\u002Fbutton>`;\n      target.appendChild(tag);\n    }\n  }\n\n  function changeAttr() {\n    const val = document.getElementById('attrVal').value.trim() || `state-${Date.now() % 1000}`;\n    target.setAttribute('data-status', val);\n    document.getElementById('attrVal').value = '';\n  }\n\n  function removeAttr() {\n    target.removeAttribute('data-status');\n  }\n\n  function changeTextNode() {\n    if (!textNode) {\n      textNode = document.createTextNode(' (text node) ');\n      target.appendChild(textNode);\n    } else {\n      textNode.textContent += '+';\n    }\n  }\n\n  function clearTextNodes() {\n    if (textNode) { textNode.remove(); textNode = null; }\n  }\n\n  function clearLog() {\n    log.innerHTML = '\u003Cdiv class=\"empty\">Log cleared — make a change above…\u003C\u002Fdiv>';\n    mutationCount = 0;\n  }",{"height":11,"autorun":12},520,true,{"slug":4,"title":14,"excerpt":15,"coverUrl":16},"You're polling setInterval to detect DOM changes. `MutationObserver` fires when they happen.","Watching for DOM mutations with setInterval or custom event dispatch is fragile and imprecise. The MutationObserver API delivers a callback exactly when attributes, text content, or child elements change — with full control over which types of mutations you watch.","\u002Fmedia\u002Fcovers\u002Fmutation-observer-dom-change-detection.png",[18,33],{"id":19,"slug":20,"name":21,"tagline":22,"description":23,"accentFrom":24,"accentTo":25,"icon":26,"defaultLocale":27,"locales":28,"features":30,"position":32},"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",[27,29],"fa",{"courses":12,"paths":12,"articles":12,"exams":31,"flashcards":31,"packages":12,"community":12,"certificates":12,"teams":12,"commerce":12},false,0,{"id":34,"slug":35,"name":36,"tagline":37,"description":38,"accentFrom":39,"accentTo":24,"icon":40,"defaultLocale":27,"locales":41,"features":43,"position":44},"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","⌘",[27,29,42],"es",{"courses":12,"paths":12,"articles":31,"exams":31,"flashcards":31,"packages":31,"community":12,"certificates":31,"teams":31,"commerce":12},2]