Feat(datetime_utility): add formatDateAsMonth

Add function to format a date as a month string
to be used in charts displaying monthly data,
specifically for the instance analytics, but this
should be useble elsewhere.

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

@@ -85,6 +85,21 @@ export const getDayName = date =>
     __('Saturday'),
   ][date.getDay()];
 
+/**
+ * Returns the i18n month name from a given date
+ * @example
+ * formatDateAsMonth(new Date('2020-06-28')) -> 'Jun'
+ * @param  {String} datetime where month is extracted from
+ * @param  {Object} options
+ * @param  {Boolean} options.abbreviated whether to use the abbreviated month string, or not
+ * @return {String} the i18n month name
+ */
+export function formatDateAsMonth(datetime, options = {}) {
+  const { abbreviated = true } = options;
+  const month = new Date(datetime).getMonth();
+  return getMonthNames(abbreviated)[month];
+}
+
 /**
  * @example
  * dateFormat('2017-12-05','mmm d, yyyy h:MMtt Z' ) -> "Dec 5, 2017 12:00am GMT+0000"

spec/frontend/lib/utils/datetime_utility_spec.js

@@ -69,6 +69,34 @@ describe('Date time utils', () => {
     });
   });
 
+  describe('formatDateAsMonth', () => {
+    it('should format dash cased date properly', () => {
+      const formattedMonth = datetimeUtility.formatDateAsMonth(new Date('2020-06-28'));
+
+      expect(formattedMonth).toBe('Jun');
+    });
+
+    it('should format return the non-abbreviated month', () => {
+      const formattedMonth = datetimeUtility.formatDateAsMonth(new Date('2020-07-28'), {
+        abbreviated: false,
+      });
+
+      expect(formattedMonth).toBe('July');
+    });
+
+    it('should format date with slashes properly', () => {
+      const formattedMonth = datetimeUtility.formatDateAsMonth(new Date('07/23/2016'));
+
+      expect(formattedMonth).toBe('Jul');
+    });
+
+    it('should format ISO date properly', () => {
+      const formattedMonth = datetimeUtility.formatDateAsMonth('2016-07-23T00:00:00.559Z');
+
+      expect(formattedMonth).toBe('Jul');
+    });
+  });
+
   describe('formatDate', () => {
     it('should format date properly', () => {
       const formattedDate = datetimeUtility.formatDate(new Date('07/23/2016'));