[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"verticals":3,"playground-structuredclone-deep-clone":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},"structuredclone-deep-clone","structuredClone vs spread vs JSON — deep clone playground",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">🧬 Deep clone showdown\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      Build a nested object with a \u003Ccode>Date\u003C\u002Fcode>, a \u003Ccode>Set\u003C\u002Fcode>, a \u003Ccode>Map\u003C\u002Fcode>,\n      and (optionally) a circular reference. Then watch \u003Ccode>{...obj}\u003C\u002Fcode>,\n      \u003Ccode>JSON.parse(JSON.stringify(obj))\u003C\u002Fcode>, and \u003Ccode>structuredClone(obj)\u003C\u002Fcode>\n      handle the exact same object three different ways.\n    \u003C\u002Fp>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> Build the object\u003C\u002Fdiv>\n      \u003Cdiv class=\"presets\">\n        \u003Cbutton class=\"btn sm\" data-preset=\"basic\" aria-pressed=\"true\">🌱 Basic (Date + Set + Map)\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-preset=\"circular\" aria-pressed=\"false\">🔁 Circular reference\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-preset=\"mapdate\" aria-pressed=\"false\">🗓️ Map & Date heavy\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cp class=\"hint\" id=\"objectHint\">\u003C\u002Fp>\n      \u003Cdiv class=\"code\" id=\"objectCode\">\u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> Clone it three ways\u003C\u002Fdiv>\n      \u003Cdiv class=\"code\" style=\"margin-bottom:14px\">const shallow    = { ...obj };\nconst roundTripped = JSON.parse(JSON.stringify(obj));\nconst trueClone    = structuredClone(obj);\u003C\u002Fdiv>\n\n      \u003Cdiv class=\"btn-row\">\n        \u003Cbutton class=\"btn primary\" id=\"mutateBtn\">Mutate the nested value\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn ghost\" id=\"resetBtn\">Reset\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"compare-grid\" id=\"compareGrid\" style=\"margin-top:14px\">\u003C\u002Fdiv>\n\n      \u003Cdiv class=\"status\" id=\"status\" style=\"margin-top:14px\" aria-live=\"polite\">\n        \u003Cspan class=\"dot info\" id=\"dot\">\u003C\u002Fspan>\u003Cspan id=\"statusText\">Loading…\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n      \u003Cp class=\"hint\">\n        Each clone is made \u003Cstrong>once\u003C\u002Fstrong>, right when you pick a preset. \"Mutate the\n        nested value\" only changes the \u003Cem>original\u003C\u002Fem> object afterwards — the checklist\n        below reveals which copies quietly followed along.\n      \u003C\u002Fp>\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\nbelow (the compare-grid \u002F clone-card \u002F row atoms).\n-->\n\u003Chtml lang=\"en\">\n\u003Chead>\n\u003Cmeta charset=\"utf-8\" \u002F>\n\u003Cmeta name=\"viewport\" content=\"width=device-width, initial-scale=1\" \u002F>\n\u003Ctitle>structuredClone vs spread vs JSON — deep clone playground\u003C\u002Ftitle>\n\u003Clink rel=\"stylesheet\" href=\"..\u002F..\u002F..\u002Fplayground\u002Fassets\u002Fbase.css\" \u002F>\n\u003Cstyle>\n  \u002F* Demo-specific CSS ONLY — base.css already provides tokens, layout, panels,\n     buttons, toggles, code blocks, status\u002Flog, banners, presets, pills. *\u002F\n\n  .compare-grid {\n    display: grid;\n    grid-template-columns: repeat(auto-fit, minmax(210px, 1fr));\n    gap: 12px;\n    margin-top: 4px;\n  }\n  .clone-card {\n    background: var(--panel-2);\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    padding: 13px 14px;\n    display: flex;\n    flex-direction: column;\n    gap: 2px;\n    min-width: 0;\n  }\n  .clone-card h3 {\n    margin: 0 0 8px;\n    font-size: 0.88rem;\n    font-weight: 800;\n    line-height: 1.35;\n    display: flex;\n    flex-wrap: wrap;\n    align-items: center;\n    justify-content: space-between;\n    gap: 6px 8px;\n  }\n  .clone-card h3 .kind-name { color: var(--ink); }\n  .clone-card .kind-code {\n    display: block;\n    font-family: var(--mono);\n    font-size: 0.72rem;\n    font-weight: 500;\n    color: var(--faint);\n    margin-top: 2px;\n  }\n  .crow {\n    display: flex;\n    flex-direction: column;\n    gap: 2px;\n    font-size: 0.79rem;\n    padding: 7px 0;\n    border-top: 1px solid var(--line-soft);\n  }\n  .crow:first-of-type { border-top: none; padding-top: 0; }\n  .crow-label {\n    font-weight: 800;\n    color: var(--muted);\n    font-size: 0.68rem;\n    text-transform: uppercase;\n    letter-spacing: 0.04em;\n  }\n  .crow-val { color: var(--ink); line-height: 1.42; word-break: break-word; }\n  .crow-val.good { color: var(--good); }\n  .crow-val.bad { color: var(--bad); }\n  .crow-val.warn { color: var(--warn); }\n  .card-error {\n    font-family: var(--mono);\n    font-size: 0.78rem;\n    color: var(--bad);\n    background: color-mix(in srgb, var(--bad) 12%, transparent);\n    border: 1px solid color-mix(in srgb, var(--bad) 40%, var(--line));\n    border-radius: var(--radius-sm);\n    padding: 9px 11px;\n    word-break: break-word;\n    line-height: 1.5;\n  }\n  .pill.warn {\n    color: var(--warn);\n    background: color-mix(in srgb, var(--warn) 16%, transparent);\n  }\n  #objectCode { margin: 0; }","\"use strict\";\nconst $ = (id) => document.getElementById(id);\n\n\u002F* ---------- the object presets ---------- *\u002F\n\nconst PRESETS = {\n  basic: () => ({\n    id: 7,\n    createdAt: new Date(\"2030-03-02T09:15:00Z\"),\n    tags: new Set([\"css\", \"js\"]),\n    settings: new Map([[\"theme\", \"dark\"], [\"lang\", \"en\"]]),\n    note: undefined,\n    profile: { count: 1, list: [1, 2, 3] },\n  }),\n  circular: () => {\n    const o = {\n      id: 13,\n      createdAt: new Date(\"2030-06-18T12:00:00Z\"),\n      tags: new Set([\"css\", \"js\"]),\n      settings: new Map([[\"theme\", \"dark\"]]),\n      note: undefined,\n      profile: { count: 1, list: [1, 2, 3] },\n    };\n    o.self = o; \u002F\u002F circular reference back to the root object\n    return o;\n  },\n  mapdate: () => ({\n    id: 21,\n    createdAt: new Date(\"2030-01-01T00:00:00Z\"),\n    archivedAt: new Date(\"2030-12-31T23:59:59Z\"),\n    tags: new Set([\"css\", \"js\", \"html\"]),\n    settings: new Map([[\"theme\", \"dark\"], [\"lang\", \"en\"], [\"region\", \"eu\"]]),\n    note: undefined,\n    profile: { count: 1, list: [1, 2, 3] },\n  }),\n};\n\nconst PRESET_HINTS = {\n  basic: \"A Date, a Set, a Map, and a nested object with an array — the exact shapes \u003Ccode>JSON.stringify\u003C\u002Fcode> mishandles.\",\n  circular: \"Same shape, plus \u003Ccode>obj.self = obj\u003C\u002Fcode> — the object holds a reference back to itself.\",\n  mapdate: \"A second Date field and a bigger Map — more type-preservation surface for the JSON round-trip to break.\",\n};\n\n\u002F* ---------- pretty-print the current object (read-only readout) ---------- *\u002F\n\nfunction inspectInline(value, rootRef) {\n  if (value === undefined) return \"undefined\";\n  if (value === null) return \"null\";\n  if (value instanceof Date) return `Date(${value.toISOString()})`;\n  if (value instanceof Map) {\n    const entries = [...value].map(([k, v]) => `${JSON.stringify(k)} => ${JSON.stringify(v)}`).join(\", \");\n    return `Map(${value.size}) {${entries}}`;\n  }\n  if (value instanceof Set) {\n    const entries = [...value].map((v) => JSON.stringify(v)).join(\", \");\n    return `Set(${value.size}) {${entries}}`;\n  }\n  if (Array.isArray(value)) return `[${value.map((v) => inspectInline(v, rootRef)).join(\", \")}]`;\n  if (typeof value === \"object\") {\n    if (value === rootRef) return \"↺ circular (points back to obj)\";\n    const entries = Object.entries(value).map(([k, v]) => `${k}: ${inspectInline(v, rootRef)}`).join(\", \");\n    return `{ ${entries} }`;\n  }\n  return JSON.stringify(value);\n}\n\nfunction inspectTop(obj) {\n  const lines = Object.entries(obj).map(([k, v]) => `  ${k}: ${inspectInline(v, obj)}`);\n  return `{\\n${lines.join(\",\\n\")}\\n}`;\n}\n\n\u002F* ---------- state ---------- *\u002F\n\nlet currentPreset = \"basic\";\nlet original = null;\nlet clones = null;\nlet mutateCount = 0;\n\nfunction safeRun(fn) {\n  try {\n    return { ok: true, value: fn() };\n  } catch (e) {\n    return { ok: false, error: (e && e.name ? e.name + \": \" : \"\") + (e && e.message ? e.message : String(e)) };\n  }\n}\n\nfunction loadPreset(name) {\n  currentPreset = name;\n  original = PRESETS[name]();\n  clones = {\n    spread: safeRun(() => ({ ...original })),\n    json: safeRun(() => JSON.parse(JSON.stringify(original))),\n    structured: safeRun(() => structuredClone(original)),\n  };\n  mutateCount = 0;\n\n  document.querySelectorAll(\".presets .btn\").forEach((b) => {\n    b.setAttribute(\"aria-pressed\", String(b.dataset.preset === name));\n  });\n  $(\"objectHint\").innerHTML = PRESET_HINTS[name];\n\n  render();\n}\n\n\u002F* ---------- rendering ---------- *\u002F\n\nfunction escapeHtml(s) {\n  return String(s).replace(\u002F[&\u003C>\"']\u002Fg, (c) => ({ \"&\": \"&\", \"\u003C\": \"<\", \">\": \">\", '\"': \""\", \"'\": \"'\" }[c]));\n}\n\nfunction row(label, state, detail) {\n  const cls = state === \"good\" || state === \"bad\" || state === \"warn\" ? state : \"\";\n  return `\u003Cdiv class=\"crow\">\u003Cspan class=\"crow-label\">${escapeHtml(label)}\u003C\u002Fspan>\u003Cspan class=\"crow-val ${cls}\">${escapeHtml(detail)}\u003C\u002Fspan>\u003C\u002Fdiv>`;\n}\n\nfunction cardShell(title, sub, pillClass, pillLabel, bodyHtml) {\n  return `\u003Cdiv class=\"clone-card\">\n    \u003Ch3>\u003Cspan class=\"kind-name\">${escapeHtml(title)}\u003C\u002Fspan>\u003Cspan class=\"pill ${pillClass}\">${escapeHtml(pillLabel)}\u003C\u002Fspan>\u003C\u002Fh3>\n    \u003Cdiv class=\"kind-code\" style=\"margin-bottom:8px\">${escapeHtml(sub)}\u003C\u002Fdiv>\n    ${bodyHtml}\n  \u003C\u002Fdiv>`;\n}\n\nfunction buildCard(kind, title, sub, res) {\n  const hasSelf = \"self\" in original;\n  const hasArchived = \"archivedAt\" in original;\n\n  if (!res.ok) {\n    return cardShell(title, sub, \"bad\", \"❌ Threw\", `\u003Cdiv class=\"card-error\">${escapeHtml(res.error)}\u003C\u002Fdiv>`);\n  }\n\n  const v = res.value;\n  let rows = \"\";\n\n  \u002F\u002F createdAt\n  if (kind === \"spread\") {\n    rows += row(\"createdAt\", \"warn\", \"same Date instance — shared, not copied\");\n  } else if (kind === \"json\") {\n    const ok = v.createdAt instanceof Date;\n    rows += row(\"createdAt\", ok ? \"good\" : \"bad\", ok ? \"Date ✓\" : `\"${v.createdAt}\" — a string, not a Date`);\n  } else {\n    const ok = v.createdAt instanceof Date && v.createdAt !== original.createdAt && v.createdAt.getTime() === original.createdAt.getTime();\n    rows += row(\"createdAt\", ok ? \"good\" : \"bad\", ok ? \"real Date, independent copy ✓\" : \"unexpected result\");\n  }\n\n  \u002F\u002F archivedAt (mapdate preset only)\n  if (hasArchived) {\n    if (kind === \"spread\") {\n      rows += row(\"archivedAt\", \"warn\", \"same Date instance — shared, not copied\");\n    } else if (kind === \"json\") {\n      const ok = v.archivedAt instanceof Date;\n      rows += row(\"archivedAt\", ok ? \"good\" : \"bad\", ok ? \"Date ✓\" : `\"${v.archivedAt}\" — a string, not a Date`);\n    } else {\n      const ok = v.archivedAt instanceof Date && v.archivedAt !== original.archivedAt;\n      rows += row(\"archivedAt\", ok ? \"good\" : \"bad\", ok ? \"real Date, independent copy ✓\" : \"unexpected result\");\n    }\n  }\n\n  \u002F\u002F tags (Set)\n  if (kind === \"spread\") {\n    rows += row(\"tags (Set)\", \"warn\", \"same Set instance — shared, not copied\");\n  } else if (kind === \"json\") {\n    const ok = v.tags instanceof Set;\n    rows += row(\"tags (Set)\", ok ? \"good\" : \"bad\", ok ? \"Set ✓\" : \"became {} — Set lost, not iterable\");\n  } else {\n    const ok = v.tags instanceof Set && v.tags !== original.tags;\n    rows += row(\"tags (Set)\", ok ? \"good\" : \"bad\", ok ? `Set(${v.tags.size}), independent copy ✓` : \"unexpected result\");\n  }\n\n  \u002F\u002F settings (Map)\n  if (kind === \"spread\") {\n    rows += row(\"settings (Map)\", \"warn\", \"same Map instance — shared, not copied\");\n  } else if (kind === \"json\") {\n    const ok = v.settings instanceof Map;\n    rows += row(\"settings (Map)\", ok ? \"good\" : \"bad\", ok ? \"Map ✓\" : \"became {} — Map lost, .get() unavailable\");\n  } else {\n    const ok = v.settings instanceof Map && v.settings !== original.settings;\n    rows += row(\"settings (Map)\", ok ? \"good\" : \"bad\", ok ? `Map(${v.settings.size}), independent copy ✓` : \"unexpected result\");\n  }\n\n  \u002F\u002F note (undefined-valued key)\n  const noteKept = \"note\" in v;\n  rows += row(\"note (undefined)\", noteKept ? \"good\" : \"bad\", noteKept ? \"key kept ✓\" : \"key dropped entirely\");\n\n  \u002F\u002F self (circular preset only)\n  if (hasSelf) {\n    if (kind === \"spread\") {\n      const pointsOriginal = v.self === original;\n      rows += row(\"self (circular)\", \"warn\", pointsOriginal ? \"points to the ORIGINAL object, not this copy\" : \"unexpected result\");\n    } else {\n      const ok = v.self === v;\n      rows += row(\"self (circular)\", ok ? \"good\" : \"bad\", ok ? \"points to this copy — graph preserved ✓\" : \"broken\");\n    }\n  }\n\n  \u002F\u002F the leak check\n  if (kind === \"spread\") {\n    const state = mutateCount === 0 ? \"warn\" : \"bad\";\n    const detail = mutateCount === 0\n      ? `${v.profile.count} — shares the original's nested object`\n      : `${v.profile.count} — updated automatically (same object as the original)`;\n    rows += row(\"profile.count\", state, detail);\n  } else {\n    rows += row(\"profile.count\", \"good\", `${v.profile.count} — independent copy, frozen at clone time`);\n  }\n\n  let pillClass, pillLabel;\n  if (kind === \"spread\") {\n    pillClass = mutateCount === 0 ? \"warn\" : \"bad\";\n    pillLabel = mutateCount === 0 ? \"🔗 Shares nested refs\" : \"🚨 Leaked after mutation\";\n  } else if (kind === \"json\") {\n    pillClass = \"bad\";\n    pillLabel = \"⚠️ Broken types\";\n  } else {\n    pillClass = \"good\";\n    pillLabel = \"✅ Correct & independent\";\n  }\n\n  return cardShell(title, sub, pillClass, pillLabel, rows);\n}\n\nfunction updateStatus() {\n  const dot = $(\"dot\");\n  const text = $(\"statusText\");\n  if (mutateCount === 0) {\n    dot.className = \"dot info\";\n    text.textContent = 'Object built and cloned three ways. Click \"Mutate the nested value\" to see which copies leak.';\n    return;\n  }\n  const spreadCount = clones.spread.ok ? clones.spread.value.profile.count : \"—\";\n  const jsonPart = clones.json.ok\n    ? `the JSON clone stays at ${clones.json.value.profile.count}`\n    : \"the JSON clone never existed — it threw on the circular reference before cloning anything\";\n  const structPart = clones.structured.ok\n    ? `structuredClone stays at ${clones.structured.value.profile.count}`\n    : \"structuredClone — unexpected error\";\n  dot.className = \"dot warn\";\n  text.textContent = `Mutated the original's profile.count to ${original.profile.count} (×${mutateCount} so far). The spread copy now shows ${spreadCount} too, because it shares that nested object with the original. But ${jsonPart}, and ${structPart} — both took an independent snapshot at clone time.`;\n}\n\nfunction render() {\n  $(\"objectCode\").textContent = inspectTop(original);\n\n  $(\"compareGrid\").innerHTML =\n    buildCard(\"spread\", \"{ ...obj }\", \"shallow copy\", clones.spread) +\n    buildCard(\"json\", \"JSON round-trip\", \"JSON.parse(JSON.stringify(obj))\", clones.json) +\n    buildCard(\"structured\", \"structuredClone(obj)\", \"true deep clone\", clones.structured);\n\n  updateStatus();\n}\n\n\u002F* ---------- wiring ---------- *\u002F\n\ndocument.querySelectorAll(\".presets .btn\").forEach((btn) => {\n  btn.addEventListener(\"click\", () => loadPreset(btn.dataset.preset));\n});\n\n$(\"mutateBtn\").addEventListener(\"click\", () => {\n  original.profile.count++;\n  original.profile.list.push(original.profile.count);\n  mutateCount++;\n  render();\n});\n\n$(\"resetBtn\").addEventListener(\"click\", () => loadPreset(currentPreset));\n\nloadPreset(\"basic\");",{"height":40,"autorun":17},520,{"slug":33,"title":42,"excerpt":43,"coverUrl":44},"You've been deep-cloning objects with a JSON hack. `structuredClone` does it right.","JSON.parse(JSON.stringify(obj)) silently corrupts Dates, Maps, Sets, and undefined values. structuredClone is the native replacement — no library, no import, no surprises.","\u002Fmedia\u002Fcovers\u002Fstructuredclone-deep-clone.png"]