In this React Calendar demo is demonstrated how to add special dates to the jqxCalendar widget. You can add any special date to the jqxCalendar by using the addSpecialDate method. When you invoke the method, you need to pass three parameters to it - Date object( the special date ), class (optional parameter which represents the css class name) and tooltip (optional parameter which displayes additional information about the special date when the user hovers it).