add duration utils docs (#35995)

packages/grafana-data/src/datetime/durationutil.ts

@@ -32,6 +32,13 @@ export function intervalToAbbreviatedDurationString(interval: Interval, includeS
   }, '');
 }
 
+/**
+ * parseDuration parses duration string into datefns Duration object
+ *
+ * @param duration - string to convert. For example '2m', '5h 20s'
+ *
+ * @public
+ */
 export function parseDuration(duration: string): Duration {
   return duration.split(' ').reduce<Duration>((acc, value) => {
     const match = value.match(/(\d+)(.+)/);
@@ -44,15 +51,37 @@ export function parseDuration(duration: string): Duration {
   }, {});
 }
 
+/**
+ * addDurationToDate adds given duration to given date and returns a new Date object
+ *
+ * @param date - date to add to. Can be either Date object or a number (milliseconds since epoch)
+ * @param duration - duration to add. For example '2m', '5h 20s'
+ *
+ * @public
+ */
 export function addDurationToDate(date: Date | number, duration: Duration): Date {
   return add(date, duration);
 }
 
+/**
+ * durationToMilliseconds convert a duration object to milliseconds
+ *
+ * @param duration - datefns Duration object
+ *
+ * @public
+ */
 export function durationToMilliseconds(duration: Duration): number {
   const now = new Date();
   return addDurationToDate(now, duration).getTime() - now.getTime();
 }
 
-export function isValidDate(dateString: string) {
+/**
+ * isValidDate returns true if given string can be parsed into valid Date object, false otherwise
+ *
+ * @param dateString - string representation of a date
+ *
+ * @public
+ */
+export function isValidDate(dateString: string): boolean {
   return !isNaN(Date.parse(dateString));
 }