Change formatCount impl to use Intl.NumberFormat (#11379)

* Change formatCount impl to use Intl.NumberFormat

* Update formatCount JSDoc description

src/utils/FormattingUtils.ts

@@ -17,28 +17,33 @@ limitations under the License.
 
 import { ReactElement, ReactNode } from "react";
 
-import { _t } from "../languageHandler";
+import { _t, getCurrentLanguage } from "../languageHandler";
 import { jsxJoin } from "./ReactUtils";
+const locale = getCurrentLanguage();
+
+// It's quite costly to instanciate `Intl.NumberFormat`, hence why we do not do
+// it in every function call
+const compactFormatter = new Intl.NumberFormat(locale, {
+    notation: "compact",
+});
 
 /**
- * formats numbers to fit into ~3 characters, suitable for badge counts
- * e.g: 999, 9.9K, 99K, 0.9M, 9.9M, 99M, 0.9B, 9.9B
+ * formats and rounds numbers to fit into ~3 characters, suitable for badge counts
+ * e.g: 999, 10K, 99K, 1M, 10M, 99M, 1B, 10B, ...
  */
 export function formatCount(count: number): string {
-    if (count < 1000) return count.toString();
-    if (count < 10000) return (count / 1000).toFixed(1) + "K";
-    if (count < 100000) return (count / 1000).toFixed(0) + "K";
-    if (count < 10000000) return (count / 1000000).toFixed(1) + "M";
-    if (count < 100000000) return (count / 1000000).toFixed(0) + "M";
-    return (count / 1000000000).toFixed(1) + "B"; // 10B is enough for anyone, right? :S
+    return compactFormatter.format(count);
 }
 
+// It's quite costly to instanciate `Intl.NumberFormat`, hence why we do not do
+// it in every function call
+const formatter = new Intl.NumberFormat(locale);
+
 /**
  * Format a count showing the whole number but making it a bit more readable.
  * e.g: 1000 => 1,000
  */
 export function formatCountLong(count: number): string {
-    const formatter = new Intl.NumberFormat();
     return formatter.format(count);
 }
 

test/utils/FormattingUtils-test.ts

@@ -0,0 +1,42 @@
+/*
+Copyright 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { formatCount, formatCountLong } from "../../src/utils/FormattingUtils";
+
+jest.mock("../../src/dispatcher/dispatcher");
+
+describe("FormattingUtils", () => {
+    describe("formatCount", () => {
+        it.each([
+            { count: 999, expectedCount: "999" },
+            { count: 9999, expectedCount: "10K" },
+            { count: 99999, expectedCount: "100K" },
+            { count: 999999, expectedCount: "1M" },
+            { count: 9999999, expectedCount: "10M" },
+            { count: 99999999, expectedCount: "100M" },
+            { count: 999999999, expectedCount: "1B" },
+            { count: 9999999999, expectedCount: "10B" },
+        ])("formats $count as $expectedCount", ({ count, expectedCount }) => {
+            expect(formatCount(count)).toBe(expectedCount);
+        });
+    });
+
+    describe("formatCountLong", () => {
+        it("formats numbers according to the locale", () => {
+            expect(formatCountLong(1000)).toBe("1,000");
+        });
+    });
+});