I got this when using attachEvent :
Expected 3 arguments, but got 2.
In the file dhtmlxscheduler.d.ts there is :
/**
* attaches the handler to an inner event of dhtmlxScheduler
* @param name the event’s name, case-insensitive
* @param handler the handler function
* @param settings optional, an object with settings for the event handler
*/
attachEvent(name: SchedulerEventName, handler: SchedulerCallback, settings: any): string;