feat: First iteration, multi themes, I18N

public/js/services/format.js

@@ -0,0 +1,25 @@
+// Locale-aware number formatting with compact notation for big values.
+
+export function createFormatter(locale) {
+  const make = (options) => new Intl.NumberFormat(locale, options);
+  const decimals = make({ maximumFractionDigits: 2 });
+  const integer = make({ maximumFractionDigits: 0 });
+  const fixed2 = make({ minimumFractionDigits: 2, maximumFractionDigits: 2 });
+  const compact = make({ notation: 'compact', maximumFractionDigits: 2 });
+  const scientific = make({ notation: 'scientific', maximumFractionDigits: 2 });
+
+  function number(n) {
+    if (!Number.isFinite(n)) return '∞';
+    const abs = Math.abs(n);
+    if (abs < 1000) return Number.isInteger(n) ? integer.format(n) : decimals.format(n);
+    if (abs < 1e6) return integer.format(n);
+    return abs < 1e15 ? compact.format(n) : scientific.format(n);
+  }
+
+  /** Amounts of money: always two decimals while small. */
+  function money(n) {
+    return Math.abs(n) < 1000 ? fixed2.format(n) : number(n);
+  }
+
+  return { number, money, price: (n) => fixed2.format(n) };
+}