The onBeforeHeaderRender event handler lets you customize the column headers of the JavaScript Calendar component.
DayPilot.Calendar.onBeforeHeaderRender(args);args.column (DayPilot.Column) - the column object (read-only)
args.header.areas (array) - an array of active area objects
args.header.backColor (string) - custom column background color
args.header.children (array) - child columns (read-only)
args.header.cssClass (string) - custom CSS class (since version 2022.4.5481)
args.header.html (string) - column HTML; if set, it will override the default content
args.header.toolTip (string) - custom column tooltip
onBeforeHeaderRender: (args) => {
args.header.html = args.column.start.toString("M/d/yyyy");
}