Create a Calendar View using FullCalendar.io, SharePoint REST, and a SharePoint Task list in SharePoint online.
This script can be greatly expanded and customized to take your calendar functionality in SharePoint to the next level.
Read my blog post at http://www.markrackley.net/2017/06/07/using-fullcalendar-io-to-create-custom-calendars-in-sharepoint/ for description and video walking you through the script.