Events

Lightsheet uses an event system for communication between the core (Sheet.ts) and UI (render.ts) components. The protocol defines UI events, prefixed with UI_, and core events, prefixed with CORE_. UI events are emitted by render.ts when data is modified in the sheet view, and core events are emitted when a change happens that should be reflected in the UI.

The event system can be accessed via Lightsheet.events. The events API allows for emitting events using Events.emit(Event), as well as subscribing to events via Events.on(EventType, ListenerFunction, EventState).

A ListenerFunction is a function with a signature of (event: Event) => void. EventState determines when the listener function is invoked, and by default is assigned to EventState.POST_EVENT. If EventState.PRE_EVENT is used instead, the listener function will be invoked before POST_EVENT listeners. This allows for modifying event contents or canceling events by modifying the canceled flag of the event object.