[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"playground-findlast-search-from-end":3,"verticals":19,"search-suggestions":46},{"slug":4,"title":5,"summary":6,"html":7,"css":8,"js":9,"config":10,"doc":13},"findlast-search-from-end","findLast() & findLastIndex() — search from the end",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">🎮 findLast() & findLastIndex(): search from the end\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      \u003Ccode>find()\u003C\u002Fcode> walks from the front and stops at the first match. \u003Ccode>findLast()\u003C\u002Fcode>\n      walks from the back and stops at the first match it reaches — the array's \u003Cstrong>last\u003C\u002Fstrong>\n      one. Pick a predicate, watch where each method lands, then reveal why\n      \u003Ccode>[...arr].reverse().find()\u003C\u002Fcode> reports the wrong position.\n    \u003C\u002Fp>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> Pick a predicate\u003C\u002Fdiv>\n      \u003Cdiv class=\"seg\" id=\"predSeg\" role=\"group\" aria-label=\"Predicate\">\n        \u003Cbutton data-pred=\"even\" aria-pressed=\"false\">value is even\u003C\u002Fbutton>\n        \u003Cbutton data-pred=\"gt5\" aria-pressed=\"false\">value > 5\u003C\u002Fbutton>\n        \u003Cbutton data-pred=\"error\" aria-pressed=\"true\">status is 'error'\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"presets\" style=\"margin-top:12px\">\n        \u003Cbutton class=\"btn sm\" data-preset=\"error\">🔥 Last error before it recovered\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-preset=\"gt5\">💰 Last big value (>5)\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-preset=\"even\">🔢 Last even value\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"btn-row\" style=\"margin-top:14px; align-items:center;\">\n        \u003Clabel class=\"toggle\">\n          \u003Cinput type=\"checkbox\" id=\"toggleOld\" \u002F>\u003Cspan class=\"switch\">\u003C\u002Fspan>\n          \u003Cspan>Reveal the old way (copy + reverse + find)\u003C\u002Fspan>\n        \u003C\u002Flabel>\n        \u003Cbutton class=\"btn ghost sm\" id=\"resetBtn\" style=\"margin-left:auto\">Reset\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> The array\u003C\u002Fdiv>\n      \u003Cdiv class=\"scan-arrows\">\n        \u003Cspan class=\"fw\">find() \u002F findIndex() scan this way →\u003C\u002Fspan>\n        \u003Cspan class=\"bw\">← findLast() \u002F findLastIndex() scan this way\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"array-row\" id=\"arrayRow\" role=\"list\" aria-label=\"Array items\">\u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">3\u003C\u002Fspan> What each method returns\u003C\u002Fdiv>\n      \u003Cdiv class=\"stat-grid\">\n        \u003Cdiv class=\"stat fw\">\n          \u003Cspan class=\"k\">find(pred)\u003C\u002Fspan>\n          \u003Cspan class=\"big-num\" id=\"findVal\">—\u003C\u002Fspan>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"stat fw\">\n          \u003Cspan class=\"k\">findIndex(pred)\u003C\u002Fspan>\n          \u003Cspan class=\"big-num\" id=\"findIdx\">—\u003C\u002Fspan>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"stat bw\">\n          \u003Cspan class=\"k\">findLast(pred)\u003C\u002Fspan>\n          \u003Cspan class=\"big-num\" id=\"findLastVal\">—\u003C\u002Fspan>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"stat bw\">\n          \u003Cspan class=\"k\">findLastIndex(pred)\u003C\u002Fspan>\n          \u003Cspan class=\"big-num\" id=\"findLastIdx\">—\u003C\u002Fspan>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"code\" id=\"codeBlock\" aria-hidden=\"true\">\u003C\u002Fdiv>\n      \u003Cdiv class=\"status good\" style=\"margin-top:12px\" role=\"status\" aria-live=\"polite\">\n        \u003Cspan class=\"dot good\">\u003C\u002Fspan>\u003Cspan id=\"statusText\">Ready.\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel old-way\" id=\"oldWayPanel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">4\u003C\u002Fspan> The old way: copy, reverse, then find\u003C\u002Fdiv>\n      \u003Cp class=\"hint\" style=\"margin-top:0\">\n        \u003Ccode>[...items].reverse()\u003C\u002Fcode> allocates a brand-new array with all\n        \u003Cspan id=\"copyCount\">8\u003C\u002Fspan> elements, then \u003Ccode>.reverse()\u003C\u002Fcode> flips that\n        \u003Cstrong>copy\u003C\u002Fstrong> in place. \u003Ccode>findIndex()\u003C\u002Fcode> then runs on the copy — so\n        the index it reports is a position \u003Cstrong>inside the copy\u003C\u002Fstrong>, not inside\n        \u003Ccode>items\u003C\u002Fcode>.\n      \u003C\u002Fp>\n      \u003Cdiv class=\"reversed-row\" id=\"reversedRow\" aria-hidden=\"true\">\u003C\u002Fdiv>\n      \u003Cdiv class=\"compare-grid\">\n        \u003Cdiv>\n          \u003Ch3 class=\"bad-h\">❌ Old way\u003C\u002Fh3>\n          \u003Cdiv class=\"code\" id=\"codeOld\">\u003C\u002Fdiv>\n        \u003C\u002Fdiv>\n        \u003Cdiv>\n          \u003Ch3 class=\"good-h\">✅ findLast way\u003C\u002Fh3>\n          \u003Cdiv class=\"code\" id=\"codeNew\">\u003C\u002Fdiv>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n      \u003Cp class=\"hint\" id=\"bugHint\">\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\n\u002F* Demo-specific CSS ONLY. base.css already provides tokens, layout, panels,\n     buttons, segmented control, toggles, code blocks, status\u002Flog, pills, etc. *\u002F\n\n  \u002F* Direction cues above the array row. *\u002F\n  .scan-arrows { display: flex; justify-content: space-between; font-size: 0.72rem;\n    font-weight: 800; letter-spacing: 0.01em; margin-bottom: 8px; }\n  .scan-arrows .fw { color: var(--info); }\n  .scan-arrows .bw { color: var(--good); }\n\n  \u002F* The array, rendered as a row of item chips. *\u002F\n  .array-row { display: flex; gap: 7px; flex-wrap: wrap; }\n  .chip { flex: 1 1 58px; min-width: 58px; text-align: center; padding: 8px 5px 7px;\n    background: var(--panel-2); border: 1px solid var(--line); border-radius: var(--radius-sm);\n    transition: border-color .15s ease, background .15s ease, transform .1s ease; }\n  .chip-top { display: flex; align-items: center; justify-content: center; gap: 5px; }\n  .chip-idx { font-family: var(--mono); font-size: 0.66rem; color: var(--faint); }\n  .chip-val { font-family: var(--mono); font-size: 1.05rem; font-weight: 800; margin-top: 3px; }\n  .chip-tags { min-height: 16px; margin-top: 6px; display: flex; gap: 3px; justify-content: center; flex-wrap: wrap; }\n  .chip-tags .pill { font-size: 0.62rem; padding: 2px 6px; }\n  .chip.match-find { border-color: var(--info); box-shadow: 0 0 0 1px var(--info) inset; transform: translateY(-1px); }\n  .chip.match-findlast { border-color: var(--good); box-shadow: 0 0 0 1px var(--good) inset; transform: translateY(-1px); }\n  .chip.match-both { border-color: var(--accent);\n    box-shadow: 0 0 0 2px var(--accent) inset;\n    background: color-mix(in srgb, var(--accent) 14%, var(--panel-2)); transform: translateY(-1px); }\n\n  \u002F* Results stat row. *\u002F\n  .stat-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 10px; margin-bottom: 12px; }\n  .stat { background: var(--panel-2); border: 1px solid var(--line); border-radius: var(--radius-sm); padding: 10px 12px; }\n  .stat .k { font-size: 0.66rem; text-transform: uppercase; letter-spacing: 0.05em; color: var(--muted); font-weight: 800; }\n  .stat .big-num { display: block; margin-top: 4px; font-size: 1.25rem; }\n  .stat.fw .big-num { color: var(--info); }\n  .stat.bw .big-num { color: var(--good); }\n\n  \u002F* Reversed-copy preview (revealed by the \"old way\" toggle). *\u002F\n  .old-way { display: none; margin-top: 14px; }\n  .old-way.show { display: block; }\n  .reversed-row { display: flex; gap: 6px; flex-wrap: wrap; margin: 4px 0 12px; }\n  .rchip { font-family: var(--mono); font-size: 0.76rem; padding: 5px 9px; border-radius: 8px;\n    background: var(--card); border: 1px solid var(--line); color: var(--muted); }\n  .rchip.hit { color: var(--ink); font-weight: 800; border-color: var(--warn);\n    background: color-mix(in srgb, var(--warn) 18%, var(--card)); }\n\n  .compare-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin-top: 10px; }\n  .compare-grid h3 { margin: 0 0 6px; font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.05em; font-weight: 800; }\n  .compare-grid .bad-h { color: var(--bad); }\n  .compare-grid .good-h { color: var(--good); }\n\n  @media (max-width: 560px) {\n    .compare-grid { grid-template-columns: 1fr; }\n  }","\"use strict\";\nconst $ = (id) => document.getElementById(id);\n\n\u002F\u002F A small fixed dataset. Every item carries both a numeric value and a status,\n\u002F\u002F so all three predicates below have real, verifiable matches — and the first\n\u002F\u002F match and last match differ for every one of them (the whole point of the demo).\nconst items = [\n  { value: 3, status: \"ok\" },    \u002F\u002F 0\n  { value: 4, status: \"ok\" },    \u002F\u002F 1  even\n  { value: 8, status: \"error\" }, \u002F\u002F 2  even, >5, error\n  { value: 1, status: \"warn\" },  \u002F\u002F 3\n  { value: 6, status: \"ok\" },    \u002F\u002F 4  even, >5\n  { value: 2, status: \"error\" }, \u002F\u002F 5  even, error\n  { value: 9, status: \"ok\" },    \u002F\u002F 6  >5\n  { value: 5, status: \"error\" }, \u002F\u002F 7  error\n];\n\nconst STATUS_DOT = { ok: \"good\", warn: \"warn\", error: \"bad\" };\n\nconst PREDICATES = {\n  even: {\n    label: \"value is even\",\n    code: \"x => x.value % 2 === 0\",\n    fn: (x) => x.value % 2 === 0,\n  },\n  gt5: {\n    label: \"value > 5\",\n    code: \"x => x.value > 5\",\n    fn: (x) => x.value > 5,\n  },\n  error: {\n    label: \"status === 'error'\",\n    code: \"x => x.status === 'error'\",\n    fn: (x) => x.status === \"error\",\n  },\n};\n\nlet currentPred = \"error\";\nlet showOld = false;\n\nfunction fmt(v) {\n  return v === undefined ? \"undefined\" : String(v);\n}\n\nfunction render() {\n  const p = PREDICATES[currentPred];\n\n  \u002F\u002F Real find()\u002FfindIndex() and findLast()\u002FfindLastIndex() calls — the actual\n  \u002F\u002F methods, run against the actual array, not simulated.\n  const findVal = items.find(p.fn);\n  const findIdx = items.findIndex(p.fn);\n  const lastVal = items.findLast(p.fn);\n  const lastIdx = items.findLastIndex(p.fn);\n\n  \u002F\u002F --- seg control state ---\n  document.querySelectorAll(\"#predSeg button\").forEach((b) => {\n    b.setAttribute(\"aria-pressed\", String(b.dataset.pred === currentPred));\n  });\n\n  \u002F\u002F --- array row ---\n  const row = $(\"arrayRow\");\n  row.innerHTML = \"\";\n  items.forEach((item, i) => {\n    const chip = document.createElement(\"div\");\n    chip.className = \"chip\";\n    chip.setAttribute(\"role\", \"listitem\");\n    const isFind = i === findIdx;\n    const isLast = i === lastIdx;\n    if (isFind && isLast) chip.classList.add(\"match-both\");\n    else if (isFind) chip.classList.add(\"match-find\");\n    else if (isLast) chip.classList.add(\"match-findlast\");\n\n    const tags = [];\n    if (isFind) tags.push('\u003Cspan class=\"pill\" style=\"color:var(--info);background:color-mix(in srgb, var(--info) 18%, transparent);\">find\u003C\u002Fspan>');\n    if (isLast) tags.push('\u003Cspan class=\"pill good\">findLast\u003C\u002Fspan>');\n\n    chip.innerHTML =\n      '\u003Cdiv class=\"chip-top\">\u003Cspan class=\"chip-idx\">[' + i + \"]\u003C\u002Fspan>\" +\n      '\u003Cspan class=\"dot ' + STATUS_DOT[item.status] + '\" title=\"status: ' + item.status + '\">\u003C\u002Fspan>\u003C\u002Fdiv>' +\n      '\u003Cdiv class=\"chip-val\">' + item.value + \"\u003C\u002Fdiv>\" +\n      '\u003Cdiv class=\"chip-tags\">' + tags.join(\"\") + \"\u003C\u002Fdiv>\";\n    row.appendChild(chip);\n  });\n\n  \u002F\u002F --- stat blocks ---\n  $(\"findVal\").textContent = findVal ? findVal.value + \" (\" + findVal.status + \")\" : \"undefined\";\n  $(\"findIdx\").textContent = fmt(findIdx === -1 ? -1 : findIdx);\n  $(\"findLastVal\").textContent = lastVal ? lastVal.value + \" (\" + lastVal.status + \")\" : \"undefined\";\n  $(\"findLastIdx\").textContent = fmt(lastIdx);\n\n  \u002F\u002F --- code readout for the two live calls ---\n  $(\"codeBlock\").innerHTML =\n    '\u003Cspan class=\"tok-kw\">const\u003C\u002Fspan> hit \u003Cspan class=\"tok-kw\">=\u003C\u002Fspan> items.\u003Cspan class=\"tok-prop\">find\u003C\u002Fspan>(\u003Cspan class=\"tok-str\">' + p.code + '\u003C\u002Fspan>); \u003Cspan class=\"tok-cmt\">\u002F\u002F index ' + findIdx + '\u003C\u002Fspan>\\n' +\n    '\u003Cspan class=\"tok-kw\">const\u003C\u002Fspan> lastHit \u003Cspan class=\"tok-kw\">=\u003C\u002Fspan> items.\u003Cspan class=\"tok-prop\">findLast\u003C\u002Fspan>(\u003Cspan class=\"tok-str\">' + p.code + '\u003C\u002Fspan>); \u003Cspan class=\"tok-cmt\">\u002F\u002F index ' + lastIdx + '\u003C\u002Fspan>';\n\n  \u002F\u002F --- status line ---\n  const gap = lastIdx - findIdx;\n  $(\"statusText\").textContent =\n    \"Predicate \\\"\" + p.label + \"\\\": find() lands on index \" + findIdx +\n    \" (value \" + findVal.value + \"). findLast() lands on index \" + lastIdx +\n    \" (value \" + lastVal.value + \") — \" + gap + \" \" + (gap === 1 ? \"position\" : \"positions\") +\n    \" further in, because it keeps going past the first match and stops at the last one.\";\n\n  renderOldWay(p, lastIdx);\n}\n\nfunction renderOldWay(p, correctIdx) {\n  if (!showOld) return;\n\n  const reversed = items.slice().reverse(); \u002F\u002F a fresh COPY, then reverse() mutates that copy\n  const reversedIdx = reversed.findIndex(p.fn); \u002F\u002F position inside the COPY\n\n  const rrow = $(\"reversedRow\");\n  rrow.innerHTML = \"\";\n  reversed.forEach((item, i) => {\n    const c = document.createElement(\"span\");\n    c.className = \"rchip\" + (i === reversedIdx ? \" hit\" : \"\");\n    c.textContent = item.value + (item.status === \"error\" ? \" ⚠\" : \"\");\n    rrow.appendChild(c);\n  });\n\n  const naiveTail = items.slice(reversedIdx); \u002F\u002F WRONG — reversedIdx is a copy's index, reused on `items`\n  const correctTail = items.slice(correctIdx); \u002F\u002F RIGHT — a real index into `items`\n\n  $(\"codeOld\").innerHTML =\n    '\u003Cspan class=\"tok-kw\">const\u003C\u002Fspan> idx \u003Cspan class=\"tok-kw\">=\u003C\u002Fspan> [...items].\u003Cspan class=\"tok-prop\">reverse\u003C\u002Fspan>().\u003Cspan class=\"tok-prop\">findIndex\u003C\u002Fspan>(\u003Cspan class=\"tok-str\">' + p.code + '\u003C\u002Fspan>);\\n' +\n    '\u003Cspan class=\"tok-cmt\">\u002F\u002F idx === ' + reversedIdx + ' — a position in the COPY\u003C\u002Fspan>\\n' +\n    '\u003Cspan class=\"tok-kw\">const\u003C\u002Fspan> tail \u003Cspan class=\"tok-kw\">=\u003C\u002Fspan> items.\u003Cspan class=\"tok-prop\">slice\u003C\u002Fspan>(idx);\\n' +\n    '\u003Cspan class=\"tok-cmt\">\u002F\u002F ' + naiveTail.length + ' of ' + items.length + ' items — wrong\u003C\u002Fspan>';\n\n  $(\"codeNew\").innerHTML =\n    '\u003Cspan class=\"tok-kw\">const\u003C\u002Fspan> idx \u003Cspan class=\"tok-kw\">=\u003C\u002Fspan> items.\u003Cspan class=\"tok-prop\">findLastIndex\u003C\u002Fspan>(\u003Cspan class=\"tok-str\">' + p.code + '\u003C\u002Fspan>);\\n' +\n    '\u003Cspan class=\"tok-cmt\">\u002F\u002F idx === ' + correctIdx + ' — a real index into items\u003C\u002Fspan>\\n' +\n    '\u003Cspan class=\"tok-kw\">const\u003C\u002Fspan> tail \u003Cspan class=\"tok-kw\">=\u003C\u002Fspan> items.\u003Cspan class=\"tok-prop\">slice\u003C\u002Fspan>(idx);\\n' +\n    '\u003Cspan class=\"tok-cmt\">\u002F\u002F ' + correctTail.length + ' of ' + items.length + ' items — correct\u003C\u002Fspan>';\n\n  $(\"bugHint\").innerHTML =\n    \"\u003Cstrong>\" + reversedIdx + \"\u003C\u002Fstrong> was found inside the reversed copy, but the code above reuses it \" +\n    \"directly against \u003Ccode>items\u003C\u002Fcode>. That slices from the wrong point and returns \u003Cstrong>\" +\n    naiveTail.length + \" item\" + (naiveTail.length === 1 ? \"\" : \"s\") + \"\u003C\u002Fstrong> instead of the \" +\n    \"\u003Cstrong>\" + correctTail.length + \"\u003C\u002Fstrong> that actually come after the last match. \" +\n    \"\u003Ccode>findLastIndex()\u003C\u002Fcode> skips the copy and the conversion — it just returns the right number.\";\n}\n\ndocument.querySelectorAll(\"#predSeg button\").forEach((btn) => {\n  btn.addEventListener(\"click\", () => {\n    currentPred = btn.dataset.pred;\n    render();\n  });\n});\n\ndocument.querySelectorAll(\"[data-preset]\").forEach((btn) => {\n  btn.addEventListener(\"click\", () => {\n    currentPred = btn.dataset.preset;\n    render();\n  });\n});\n\n$(\"toggleOld\").addEventListener(\"change\", (e) => {\n  showOld = e.target.checked;\n  $(\"oldWayPanel\").classList.toggle(\"show\", showOld);\n  if (showOld) render();\n});\n\n$(\"resetBtn\").addEventListener(\"click\", () => {\n  currentPred = \"error\";\n  showOld = false;\n  $(\"toggleOld\").checked = false;\n  $(\"oldWayPanel\").classList.remove(\"show\");\n  render();\n});\n\n$(\"copyCount\").textContent = String(items.length);\nrender();",{"height":11,"autorun":12},520,true,{"slug":4,"title":14,"excerpt":15,"coverUrl":16,"vertical":17},"You copy and reverse the array to find the last match. `findLast()` searches from the end directly.","The usual workaround — `[...arr].reverse().find()` — allocates a full copy just to walk it backward. ES2023 added `findLast()` and `findLastIndex()` to search from the end without touching the original.","\u002Fmedia\u002Fcovers\u002Ffindlast-search-from-end.png",{"slug":18},"dev",[20,34],{"id":21,"slug":18,"name":22,"tagline":23,"description":24,"accentFrom":25,"accentTo":26,"icon":27,"defaultLocale":28,"locales":29,"features":31,"position":33},"019fe637-3d33-714b-b57f-23e163ffca0c","Web Development","Build. Learn. 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