Function dispatchEvent

packages/react-native-renderer/src/ReactFabricEventEmitter.js:84–139

(
  target: null | Object,
  topLevelType: RNTopLevelEventType,
  nativeEvent: AnyNativeEvent,
)

}

export function dispatchEvent(
  target: null | Object,
  topLevelType: RNTopLevelEventType,
  nativeEvent: AnyNativeEvent,
) {
  const targetFiber = (target: null | Fiber);

  let eventTarget = null;
  if (targetFiber != null) {
    const stateNode = targetFiber.stateNode;
    // Guard against Fiber being unmounted
    if (stateNode != null) {
      // $FlowExpectedError[incompatible-cast] public instances in Fabric do not implement `EventTarget` yet.
      eventTarget = (getPublicInstance(stateNode): EventTarget);
    }
  }

  batchedUpdates(function () {
    // Emit event to the RawEventEmitter. This is an unused-by-default EventEmitter
    // that can be used to instrument event performance monitoring (primarily - could be useful
    // for other things too).
    //
    // NOTE: this merely emits events into the EventEmitter below.
    // If *you* do not add listeners to the `RawEventEmitter`,
    // then all of these emitted events will just blackhole and are no-ops.
    // It is available (although not officially supported... yet) if you want to collect
    // perf data on event latency in your application, and could also be useful for debugging
    // low-level events issues.
    //
    // If you do not have any event perf monitoring and are extremely concerned about event perf,
    // it is safe to disable these "emit" statements; it will prevent checking the size of
    // an empty array twice and prevent two no-ops. Practically the overhead is so low that
    // we don't think it's worth thinking about in prod; your perf issues probably lie elsewhere.
    //
    // We emit two events here: one for listeners to this specific event,
    // and one for the catchall listener '*', for any listeners that want
    // to be notified for all events.
    // Note that extracted events are *not* emitted,
    // only events that have a 1:1 mapping with a native event, at least for now.
    const event = {eventName: topLevelType, nativeEvent};
    // $FlowFixMe[class-object-subtyping] found when upgrading Flow
    RawEventEmitter.emit(topLevelType, event);
    // $FlowFixMe[class-object-subtyping] found when upgrading Flow
    RawEventEmitter.emit('*', event);

    // Heritage plugin event system
    runExtractedPluginEventsInBatch(
      topLevelType,
      targetFiber,
      nativeEvent,
      eventTarget,
    );
  });
  // React Native doesn't use ReactControlledComponent but if it did, here's
  // where it would do it.
}