util: Defining common formatter function

web/src/util.ts

@@ -4,6 +4,7 @@ import * as blueslip from "./blueslip";
 import {$t} from "./i18n";
 import type {MatchedMessage, Message, RawMessage} from "./message_store";
 import type {UpdateMessageEvent} from "./types";
+import {user_settings} from "./user_settings";
 
 // From MDN: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Math/random
 export function random_int(min: number, max: number): number {
@@ -489,3 +490,21 @@ export function is_valid_url(url: string, require_absolute = false): boolean {
     }
     return true;
 }
+
+// Formats an array of strings as a Internationalized list using the specified language.
+export function format_array_as_list(
+    array: string[],
+    style: Intl.ListFormatStyle,
+    type: Intl.ListFormatType,
+): string {
+    // If Intl.ListFormat is not supported
+    if (Intl.ListFormat === undefined) {
+        return array.join(", ");
+    }
+
+    // Use Intl.ListFormat to format the array as a Internationalized list.
+    const list_formatter = new Intl.ListFormat(user_settings.default_language, {style, type});
+
+    // Return the formatted string.
+    return list_formatter.format(array);
+}

web/tests/util.test.js

@@ -338,3 +338,16 @@ run_test("is_valid_url", () => {
     assert.equal(util.is_valid_url("http://google.com/something?q=query#hash", true), true);
     assert.equal(util.is_valid_url("/abc/", true), false);
 });
+
+run_test("format_array_as_list", () => {
+    const array = ["apple", "banana", "orange"];
+    // when Intl exist
+    assert.equal(
+        util.format_array_as_list(array, "long", "conjunction"),
+        "apple, banana, and orange",
+    );
+
+    // when Intl.ListFormat does not exist
+    global.Intl.ListFormat = undefined;
+    assert.equal(util.format_array_as_list(array, "long", "conjunction"), "apple, banana, orange");
+});