Add grammar util

This contains the function `toNounSeriesText` which can be used to build
i18n noun series fragments (i.e. "A, B, and C").

app/assets/javascripts/lib/utils/grammar.js

+import { sprintf, s__ } from '~/locale';
+
+/**
+ * Combines each given item into a noun series sentence fragment. It does this
+ * in a way that supports i18n by giving context and punctuation to the locale
+ * functions.
+ *
+ * **Examples:**
+ *
+ * - `["A", "B"] => "A and B"`
+ * - `["A", "B", "C"] => "A, B, and C"`
+ *
+ * **Why only nouns?**
+ *
+ * Some languages need a bit more context to translate other series.
+ *
+ * @param {String[]} items
+ */
+export const toNounSeriesText = items => {
+  if (items.length === 0) {
+    return '';
+  } else if (items.length === 1) {
+    return items[0];
+  } else if (items.length === 2) {
+    return sprintf(s__('nounSeries|%{firstItem} and %{lastItem}'), {
+      firstItem: items[0],
+      lastItem: items[1],
+    });
+  }
+
+  return items.reduce((item, nextItem, idx) =>
+    idx === items.length - 1
+      ? sprintf(s__('nounSeries|%{item}, and %{lastItem}'), { item, lastItem: nextItem })
+      : sprintf(s__('nounSeries|%{item}, %{nextItem}'), { item, nextItem }),
+  );
+};
+
+export default {
+  toNounSeriesText,
+};

locale/gitlab.pot

@@ -8706,6 +8706,15 @@ msgstr ""
 msgid "notification emails"
 msgstr ""
 
+msgid "nounSeries|%{firstItem} and %{lastItem}"
+msgstr ""
+
+msgid "nounSeries|%{item}, %{nextItem}"
+msgstr ""
+
+msgid "nounSeries|%{item}, and %{lastItem}"
+msgstr ""
+
 msgid "or"
 msgstr ""
 

spec/javascripts/lib/utils/grammar_spec.js

+import * as grammar from '~/lib/utils/grammar';
+
+describe('utils/grammar', () => {
+  describe('toNounSeriesText', () => {
+    it('with empty items returns empty string', () => {
+      expect(grammar.toNounSeriesText([])).toBe('');
+    });
+
+    it('with single item returns item', () => {
+      const items = ['Lorem Ipsum'];
+
+      expect(grammar.toNounSeriesText(items)).toBe(items[0]);
+    });
+
+    it('with 2 items returns item1 and item2', () => {
+      const items = ['Dolar', 'Sit Amit'];
+
+      expect(grammar.toNounSeriesText(items)).toBe(`${items[0]} and ${items[1]}`);
+    });
+
+    it('with 3 items returns comma separated series', () => {
+      const items = ['Lorem', 'Ipsum', 'dolar'];
+      const expected = 'Lorem, Ipsum, and dolar';
+
+      expect(grammar.toNounSeriesText(items)).toBe(expected);
+    });
+
+    it('with 6 items returns comma separated series', () => {
+      const items = ['Lorem', 'ipsum', 'dolar', 'sit', 'amit', 'consectetur'];
+      const expected = 'Lorem, ipsum, dolar, sit, amit, and consectetur';
+
+      expect(grammar.toNounSeriesText(items)).toBe(expected);
+    });
+  });
+});