Event Bus & Wiring

Modules in dash.js communicate through two channels: the EventBus for anything event-shaped, and explicit setConfig({...}) wiring for hard dependencies.

EventBus

The event bus (src/core/EventBus.js) is a context-scoped singleton — each player instance has its own:

const eventBus = EventBus(context).getInstance();

eventBus.on(Events.BYTES_APPENDED_END_FRAGMENT, _onBytesAppended, instance);
eventBus.off(Events.BYTES_APPENDED_END_FRAGMENT, _onBytesAppended, instance);
eventBus.trigger(Events.BUFFER_LEVEL_UPDATED, { mediaType, bufferLevel });

Subscriptions support priorities. A listener registered with EVENT_PRIORITY_HIGH (5000) runs before the default EVENT_PRIORITY_LOW (0) listeners — internal controllers use this when ordering matters:

eventBus.on(Events.PLAYBACK_SEEKING, _onPlaybackSeeking, instance, { priority: EventBus.EVENT_PRIORITY_HIGH });

once() registers a self-removing listener, and trigger() accepts filters (e.g. streamId, mediaType) so listeners only receive events for their own stream or media type.

Three event surfaces

Surface	Defined in	Audience
Core events	src/core/events/ (Events.js, CoreEvents.js)	Internal module-to-module communication. Not part of the public API — may change without notice.
MediaPlayer events	src/streaming/MediaPlayerEvents.js	Public API. Applications subscribe via player.on(dashjs.MediaPlayer.events.X, ...). See Player Events.
Protection events	src/streaming/protection/ProtectionEvents.js	Public DRM-related events (license requests, key statuses).

Applications should only rely on MediaPlayerEvents and ProtectionEvents.

Explicit wiring via setConfig

Hard dependencies are passed explicitly. During initialization, the creating module injects the collaborators a module needs:

gapController.setConfig({
    settings,
    playbackController,
    streamController,
    videoModel,
    timelineConverter,
    adapter
});

This keeps the dependency graph visible and testable — unit tests replace collaborators with mocks (test/unit/mocks/) by calling setConfig() with test doubles.

Rule of thumb: state changes and notifications go over the EventBus; direct queries and commands go through injected references.