Adding comments to helper methods in Drive Activity v2 API quickstart.

drive/activity-v2/index.html

@@ -1,5 +1,5 @@
 <!--
-Copyright 2018 Google LLC
+Copyright 2019 Google LLC
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
@@ -140,19 +140,22 @@
             });
       }
 
+      /** Returns a string representation of the first elements in a list. */
       function truncated(array, limit = 2) {
         var contents = array.slice(0, limit).join(', ');
         var more = array.length > limit ? ', ...' : '';
         return `[${contents}${more}]`;
       }
 
+      /** Returns the name of a set property in an object, or else "unknown". */
       function getOneOf(object) {
         for (var key in object) {
           return key;
         }
         return 'unknown';
       }
 
+      /** Returns a time associated with an activity. */
       function getTimeInfo(activity) {
         if ('timestamp' in activity) {
           return activity.timestamp;
@@ -163,10 +166,12 @@
         return 'unknown';
       }
 
+      /** Returns the type of action. */
       function getActionInfo(actionDetail) {
         return getOneOf(actionDetail);
       }
 
+      /** Returns user information, or the type of user if not a known user. */
       function getUserInfo(user) {
         if ('knownUser' in user) {
           var knownUser = user['knownUser'];
@@ -176,13 +181,15 @@
         return getOneOf(user);
       }
 
+      /** Returns actor information, or the type of actor if not a user. */
       function getActorInfo(actor) {
         if ('user' in actor) {
           return getUserInfo(actor['user'])
         }
         return getOneOf(actor);
       }
 
+      /** Returns the type of a target and an associated title. */
       function getTargetInfo(target) {
         if ('driveItem' in target) {
           var title = target.driveItem.title || 'unknown';