Add type annotation for some js files (#24787)

app/javascript/mastodon/utils/numbers.ts

@@ -0,0 +1,71 @@
+import type { ValueOf } from '../../types/util';
+
+export const DECIMAL_UNITS = Object.freeze({
+  ONE: 1,
+  TEN: 10,
+  HUNDRED: 100,
+  THOUSAND: 1_000,
+  MILLION: 1_000_000,
+  BILLION: 1_000_000_000,
+  TRILLION: 1_000_000_000_000,
+});
+export type DecimalUnits = ValueOf<typeof DECIMAL_UNITS>;
+
+const TEN_THOUSAND = DECIMAL_UNITS.THOUSAND * 10;
+const TEN_MILLIONS = DECIMAL_UNITS.MILLION * 10;
+
+/**
+ * @param {number} sourceNumber Number to convert to short number
+ * @returns {ShortNumber} Calculated short number
+ * @example
+ * shortNumber(5936);
+ * // => [5.936, 1000, 1]
+ */
+export type ShortNumber = [number, DecimalUnits, 0 | 1] // Array of: shorten number, unit of shorten number and maximum fraction digits
+export function toShortNumber(sourceNumber: number): ShortNumber {
+  if (sourceNumber < DECIMAL_UNITS.THOUSAND) {
+    return [sourceNumber, DECIMAL_UNITS.ONE, 0];
+  } else if (sourceNumber < DECIMAL_UNITS.MILLION) {
+    return [
+      sourceNumber / DECIMAL_UNITS.THOUSAND,
+      DECIMAL_UNITS.THOUSAND,
+      sourceNumber < TEN_THOUSAND ? 1 : 0,
+    ];
+  } else if (sourceNumber < DECIMAL_UNITS.BILLION) {
+    return [
+      sourceNumber / DECIMAL_UNITS.MILLION,
+      DECIMAL_UNITS.MILLION,
+      sourceNumber < TEN_MILLIONS ? 1 : 0,
+    ];
+  } else if (sourceNumber < DECIMAL_UNITS.TRILLION) {
+    return [
+      sourceNumber / DECIMAL_UNITS.BILLION,
+      DECIMAL_UNITS.BILLION,
+      0,
+    ];
+  }
+
+  return [sourceNumber, DECIMAL_UNITS.ONE, 0];
+}
+
+/**
+ * @param {number} sourceNumber Original number that is shortened
+ * @param {number} division The scale in which short number is displayed
+ * @returns {number} Number that can be used for plurals when short form used
+ * @example
+ * pluralReady(1793, DECIMAL_UNITS.THOUSAND)
+ * // => 1790
+ */
+export function pluralReady(sourceNumber: number, division: DecimalUnits): number {
+  if (division == null || division < DECIMAL_UNITS.HUNDRED) {
+    return sourceNumber;
+  }
+
+  const closestScale = division / DECIMAL_UNITS.TEN;
+
+  return Math.trunc(sourceNumber / closestScale) * closestScale;
+}
+
+export function roundTo10(num: number): number {
+  return Math.round(num * 0.1) / 0.1;
+}