The onBeforeEventRender event is fired before the JavaScript Calendar renders an event. It lets you customize the event properties dynamically.
DayPilot.Calendar.onBeforeEventRender(args);args.control - DayPilot.Calendar reference; available since 2023.3.5716
args.data - a shallow copy of the raw event data object
dp.onBeforeEventRender = function(args) {
args.data.cssClass = "test";
args.data.html = args.data.text + ":";
};