[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"verticals":3,"playground-intl-numberformat-currency-formatting":44,"search-suggestions":58},[4,20,32],{"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","Read it. Run it. Prove it.","A post a day on modern web development — most with an editable playground and a quiz that explains every answer. Free, no account needed.","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.","Grammar explained the way good documentation explains an API — one idea at a time, each with a quiz.","amber-400","⌘",[13,15,29],"es",{"courses":18,"paths":18,"articles":17,"exams":18,"flashcards":17,"packages":18,"community":17,"certificates":17,"teams":18,"commerce":18},2,{"id":33,"slug":34,"name":35,"tagline":36,"description":37,"accentFrom":38,"accentTo":39,"icon":40,"defaultLocale":13,"locales":41,"features":42,"position":43},"7b3c16f2-931d-410e-802e-e1fa4edab7de","soft","Soft Skills","The half of the job nobody wrote documentation for.","Weekly, on the parts of working life that decide more than your code does — first weeks, meetings, interviews, promotions, and the people around you. Written from what actually happens, and recorded as a podcast you can listen to on the walk.","emerald-400","teal-300","◉",[13],{"courses":18,"paths":18,"articles":17,"exams":18,"flashcards":18,"packages":18,"community":17,"certificates":18,"teams":18,"commerce":18},3,{"slug":45,"title":46,"summary":47,"html":48,"css":49,"js":50,"config":51,"doc":53},"intl-numberformat-currency-formatting","Intl.NumberFormat vs. hand-rolled formatMoney()",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">🎮 Intl.NumberFormat vs. hand-rolled formatMoney()\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      Same amount, same currency, two formatters. Change the locale, the decimal\n      places, or try a preset bug — \u003Ccode>Intl.NumberFormat\u003C\u002Fcode> adapts; the\n      regex-based formatter doesn't know it's wrong.\n    \u003C\u002Fp>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> Controls\u003C\u002Fdiv>\n      \u003Cdiv class=\"field-row\">\n        \u003Cdiv class=\"field\">\n          Amount\n          \u003Cinput type=\"number\" id=\"amount\" value=\"1234.5\" step=\"any\" \u002F>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"field\">\n          Decimal places\n          \u003Cinput type=\"number\" id=\"decimals\" value=\"2\" min=\"0\" max=\"6\" \u002F>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"field\">\n          Locale\n          \u003Cselect id=\"locale\">\n            \u003Coption value=\"en-US\">en-US\u003C\u002Foption>\n            \u003Coption value=\"de-DE\">de-DE\u003C\u002Foption>\n            \u003Coption value=\"fr-FR\">fr-FR\u003C\u002Foption>\n          \u003C\u002Fselect>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"field\">\n          Currency\n          \u003Cselect id=\"currency\">\n            \u003Coption value=\"USD\">USD\u003C\u002Foption>\n            \u003Coption value=\"EUR\">EUR\u003C\u002Foption>\n            \u003Coption value=\"GBP\">GBP\u003C\u002Foption>\n          \u003C\u002Fselect>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"presets\" style=\"margin-top:10px\">\n        \u003Cbutton class=\"btn sm\" data-preset=\"basic\">Basic price\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-preset=\"refund\">Refund (negative)\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-preset=\"unitcost\">Per-unit cost (4 decimals)\u003C\u002Fbutton>\n        \u003Cbutton class=\"btn sm\" data-preset=\"german\">German customer, same price\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> Result\u003C\u002Fdiv>\n      \u003Cdiv class=\"compare\">\n        \u003Cdiv class=\"outbox\" id=\"naiveBox\">\n          \u003Cdiv class=\"who\">Hand-rolled formatMoney()\u003C\u002Fdiv>\n          \u003Cdiv class=\"val\" id=\"naiveOut\">$1,234.50\u003C\u002Fdiv>\n          \u003Cspan class=\"tag\" id=\"naiveTag\">looks fine\u003C\u002Fspan>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"outbox good\" id=\"intlBox\">\n          \u003Cdiv class=\"who\">Intl.NumberFormat\u003C\u002Fdiv>\n          \u003Cdiv class=\"val\" id=\"intlOut\">$1,234.50\u003C\u002Fdiv>\n          \u003Cspan class=\"tag\">correct for this locale\u003C\u002Fspan>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"status\" id=\"statusRow\" style=\"margin-top:12px\">\n        \u003Cspan class=\"dot good\" id=\"dot\">\u003C\u002Fspan>\u003Cspan id=\"statusText\">Both formatters agree.\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n      \u003Cp class=\"hint\" id=\"hint\">\n        The regex formatter always uses \"$\" and comma\u002Fperiod the US way, no matter which\n        locale you pick — it can't do otherwise, because it never read the locale in the\n        first place.\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\n\u002F* Demo-specific CSS only — base.css owns tokens, .panel, .btn, .toggle, .code, .status. *\u002F\n\n  .field-row {\n    display: flex;\n    flex-wrap: wrap;\n    gap: 14px;\n    align-items: flex-end;\n    margin-bottom: 4px;\n  }\n  .field {\n    display: flex;\n    flex-direction: column;\n    gap: 4px;\n    font-size: 0.82rem;\n    color: var(--muted);\n    font-weight: 600;\n  }\n  .field input[type=\"number\"],\n  .field select {\n    font-family: var(--mono);\n    font-size: 0.95rem;\n    padding: 7px 9px;\n    border-radius: var(--radius-sm);\n    border: 1px solid var(--line);\n    background: var(--panel-2);\n    color: var(--ink);\n    min-width: 110px;\n  }\n  .compare {\n    display: grid;\n    grid-template-columns: 1fr;\n    gap: 12px;\n    margin-top: 14px;\n  }\n  @media (min-width: 560px) {\n    .compare { grid-template-columns: 1fr 1fr; }\n  }\n  .outbox {\n    border: 2px solid var(--line);\n    border-radius: var(--radius-sm);\n    padding: 12px 14px;\n    background: var(--panel-2);\n  }\n  .outbox .who {\n    font-size: 0.72rem;\n    font-weight: 700;\n    letter-spacing: .03em;\n    text-transform: uppercase;\n    color: var(--muted);\n    margin-bottom: 6px;\n  }\n  .outbox .val {\n    font-family: var(--mono);\n    font-size: 1.35rem;\n    font-weight: 700;\n    color: var(--ink);\n    word-break: break-all;\n  }\n  .outbox.bad { border-color: var(--warn); }\n  .outbox.good { border-color: var(--good); }\n  .outbox .tag {\n    display: inline-block;\n    margin-top: 8px;\n    font-size: 0.72rem;\n    font-weight: 700;\n    padding: 2px 8px;\n    border-radius: 999px;\n  }\n  .outbox.bad .tag { background: var(--warn); color: #1a1300; }\n  .outbox.good .tag { background: var(--good); color: #06220d; }","\"use strict\";\n  const $ = (id) => document.getElementById(id);\n\n  function formatMoneyNaive(amount, decimals) {\n    \u002F\u002F The never-patched regex formatter from the article's opening example —\n    \u002F\u002F no sign handling, no locale awareness — so every preset below shows\n    \u002F\u002F exactly the bug it's named for.\n    return \"$\" + amount.toFixed(decimals).replace(\u002F\\B(?=(\\d{3})+(?!\\d))\u002Fg, \",\");\n  }\n\n  function run() {\n    const amount = parseFloat($(\"amount\").value);\n    const decimals = Math.max(0, Math.min(6, parseInt($(\"decimals\").value, 10) || 0));\n    const locale = $(\"locale\").value;\n    const currency = $(\"currency\").value;\n\n    if (Number.isNaN(amount)) {\n      $(\"naiveOut\").textContent = \"—\";\n      $(\"intlOut\").textContent = \"—\";\n      setStatus(\"Enter a number above.\", \"info\");\n      return;\n    }\n\n    const naive = formatMoneyNaive(amount, decimals);\n    const intl = new Intl.NumberFormat(locale, {\n      style: \"currency\",\n      currency,\n      minimumFractionDigits: decimals,\n      maximumFractionDigits: decimals,\n    }).format(amount);\n\n    $(\"naiveOut\").textContent = naive;\n    $(\"intlOut\").textContent = intl;\n\n    const naiveBox = $(\"naiveBox\");\n    const naiveTag = $(\"naiveTag\");\n\n    \u002F\u002F The regex formatter breaks in a few distinct ways: it puts the sign in\n    \u002F\u002F the wrong place, it mis-groups the fractional part once there are more\n    \u002F\u002F than 3 decimal digits, or it ignores the requested locale\u002Fcurrency\n    \u002F\u002F entirely. Falling back to a plain string mismatch catches anything\n    \u002F\u002F those three specific checks miss.\n    const wrongSign = amount \u003C 0 && !naive.startsWith(\"-\");\n    const hasDecimalBug = \u002F\\.\\d*,\u002F.test(naive);\n    const wrongLocale = locale !== \"en-US\" || currency !== \"USD\";\n    const disagree = naive !== intl;\n\n    if (wrongSign) {\n      naiveBox.className = \"outbox bad\";\n      naiveTag.textContent = \"sign in the wrong place\";\n      setStatus('The \"-\" landed after the \"$\" instead of before it — ' + naive + \" isn't a number a parser (or a customer) reads correctly.\", \"warn\");\n    } else if (hasDecimalBug) {\n      naiveBox.className = \"outbox bad\";\n      naiveTag.textContent = \"comma inside the decimal part\";\n      setStatus(\"The regex grouped the fractional digits too — that's not a valid number.\", \"warn\");\n    } else if (wrongLocale) {\n      naiveBox.className = \"outbox bad\";\n      naiveTag.textContent = \"wrong for \" + locale + \" \u002F \" + currency;\n      setStatus(\"The regex formatter can't speak \" + locale + \" — it only knows US formatting.\", \"warn\");\n    } else if (disagree) {\n      naiveBox.className = \"outbox bad\";\n      naiveTag.textContent = \"doesn't match Intl.NumberFormat\";\n      setStatus(\"The two formatters produced different output for this input.\", \"warn\");\n    } else {\n      naiveBox.className = \"outbox\";\n      naiveTag.textContent = \"looks fine (for now)\";\n      setStatus(\"Both formatters agree — try a different locale or more decimals.\", \"good\");\n    }\n  }\n\n  function setStatus(text, kind) {\n    $(\"statusText\").textContent = text;\n    $(\"dot\").className = \"dot \" + kind;\n  }\n\n  const PRESETS = {\n    basic: { amount: 1234.5, decimals: 2, locale: \"en-US\", currency: \"USD\" },\n    refund: { amount: -1234.5, decimals: 2, locale: \"en-US\", currency: \"USD\" },\n    unitcost: { amount: 1234.5678, decimals: 4, locale: \"en-US\", currency: \"USD\" },\n    german: { amount: 1234.5, decimals: 2, locale: \"de-DE\", currency: \"EUR\" },\n  };\n\n  document.querySelectorAll(\"[data-preset]\").forEach((btn) => {\n    btn.addEventListener(\"click\", () => {\n      const p = PRESETS[btn.dataset.preset];\n      $(\"amount\").value = p.amount;\n      $(\"decimals\").value = p.decimals;\n      $(\"locale\").value = p.locale;\n      $(\"currency\").value = p.currency;\n      run();\n    });\n  });\n\n  [\"amount\", \"decimals\", \"locale\", \"currency\"].forEach((id) => {\n    $(id).addEventListener(\"input\", run);\n    $(id).addEventListener(\"change\", run);\n  });\n\n  run();",{"height":52,"autorun":17},520,{"slug":45,"title":54,"excerpt":55,"coverUrl":56,"vertical":57},"Stop Formatting Currency With Regex. `Intl.NumberFormat` Does It.","A hand-rolled formatMoney() with toFixed() and a comma regex looks fine in a US demo and quietly breaks the moment a real user, a negative balance, or a non-dollar locale shows up. Intl.NumberFormat has handled all of it, built into every modern browser, since before most teams' codebases existed.","\u002Fmedia\u002Fcovers\u002Fintl-numberformat-currency-formatting.png",{"slug":6},[59,63,67,71,75,79,83,87,91,95,99,102],{"slug":60,"name":61,"articles":62},"webdev","Webdev",148,{"slug":64,"name":65,"articles":66},"javascript","Javascript",121,{"slug":68,"name":69,"articles":70},"frontend","Frontend",87,{"slug":72,"name":73,"articles":74},"tutorial","Tutorial",57,{"slug":76,"name":77,"articles":78},"css","Css",44,{"slug":80,"name":81,"articles":82},"performance","Performance",24,{"slug":84,"name":85,"articles":86},"typescript","Typescript",20,{"slug":88,"name":89,"articles":90},"react","React",18,{"slug":92,"name":93,"articles":94},"browser","Browser",14,{"slug":96,"name":97,"articles":98},"programming","Programming",12,{"slug":100,"name":101,"articles":98},"node","Node",{"slug":103,"name":104,"articles":105},"accessibility","Accessibility",10]