Add new localeFormat API for locale-based formatting (using Intl API)

src/locale.ts

@@ -0,0 +1,29 @@
+/**
+ * Use this API for locale-based formatting.
+ * @param {Date}  date - Date object, which should be used.
+ * @param {string} exp - String, which you want to format, for example: {yyyy}-{MM}-{dd} or Current time: {hh}:{mm}:{ss}.
+ * @param {string | string[] = 'en-US'} locale - Locale(s), which will be used for formatting.
+ * @return {string} String with formatted date.
+ */
+export default (date: Date, exp: string, locale: string | string[] = 'en-US'): string => exp.replace(/{.*?}/g, key => {
+	const shortWeekday = new Intl.DateTimeFormat(locale, {weekday: 'short'}).format(date);
+	switch (key) {
+		case '{MMMMM}':
+			return new Intl.DateTimeFormat(locale, {month: 'narrow'}).format(date);
+		case '{MMMM}':
+			return new Intl.DateTimeFormat(locale, {month: 'long'}).format(date);
+		case '{MMM}':
+			return new Intl.DateTimeFormat(locale, {month: 'short'}).format(date);
+		case '{EEEEE}':
+			return new Intl.DateTimeFormat(locale, {weekday: 'narrow'}).format(date);
+		case '{EEEE}':
+			return new Intl.DateTimeFormat(locale, {weekday: 'long'}).format(date);
+		case '{EEE}':
+		case '{EE}':
+		case '{E}':
+			return shortWeekday;
+		/* c8 ignore next 2 */
+		default:
+			return '';
+	}
+});

test/locale.ts

@@ -0,0 +1,17 @@
+import test from 'ava';
+import {localeFormat} from '../src';
+
+const foo = new Date('8/1/2020, 4:30:09 PM');
+
+test('general', t => {
+	t.is(localeFormat(foo, 'foo'), 'foo', 'does nothing if no match');
+	t.is(localeFormat(foo, 'MMM'), 'MMM', 'does nothing if no `{}` wrappers');
+	t.is(localeFormat(foo, '{MMM}'), 'Aug', 'returns abbreviated month');
+	t.is(localeFormat(foo, '{MMMM}'), 'August', 'returns wide month');
+	t.is(localeFormat(foo, '{MMMMM}'), 'A', 'returns narrow month');
+	t.is(localeFormat(foo, '{E}'), 'Sat', 'returns abbreviated day of week');
+	t.is(localeFormat(foo, '{EE}'), 'Sat', 'returns abbreviated day of week');
+	t.is(localeFormat(foo, '{EEE}'), 'Sat', 'returns abbreviated day of week');
+	t.is(localeFormat(foo, '{EEEE}'), 'Saturday', 'returns wide day of week');
+	t.is(localeFormat(foo, '{EEEEE}'), 'S', 'returns narrow day of week');
+});