Regularly trigger ADD_CALENDAR to ensure calendar fetcher is running

CHANGELOG.md

@@ -37,6 +37,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Calendar: Fix relative date handling for fulldate events, calculate difference always from start of day  [#1572](https://github.com/MichMich/MagicMirror/issues/1572)
 - Fix null dereference in moduleNeedsUpdate when the module isn't visible
 - Calendar: Fixed event end times by setting default calendarEndTime to "LT" (Local time format). [#1479]
+- Calendar: Fixed missing calendar fetchers after server process restarts [#1589](https://github.com/MichMich/MagicMirror/issues/1589)
 
 ### New weather module
 - Fixed weather forecast table display [#1499](https://github.com/MichMich/MagicMirror/issues/1499).

modules/default/calendar/calendar.js

@@ -105,6 +105,13 @@ Module.register("calendar", {
 			}
 
 			this.addCalendar(calendar.url, calendar.auth, calendarConfig);
+
+			// Trigger ADD_CALENDAR every fetchInterval to make sure there is always a calendar
+			// fetcher running on the server side.
+			var self = this;
+			setInterval(function() {
+				self.addCalendar(calendar.url, calendar.auth, calendarConfig);
+			}, self.config.fetchInterval);
 		}
 
 		this.calendarData = {};