Example RCTEventEmitter Subclass

GSEventEmitter.h

#import "RCTEventEmitter.h"
#import "RCTBridge.h"

@interface GSEventEmitter : RCTEventEmitter <RCTBridgeModule>

+ (BOOL)application:(UIApplication *)application didSightBeacon:(NSString *)beaconID;
+ (BOOL)application:(UIApplication *)application didDepartBeacon:(NSString *)beaconID;

@end

GSEventEmitter.m

#import "GSEventEmitter.h"

// Notification/Event Names
NSString *const kBeaconSighted = @"GSEventEmitter/beaconSighted";
NSString *const kBeaconDeparted = @"GSEventEmitter/beaconDeparted";

@implementation GSEventEmitter
  
RCT_EXPORT_MODULE();

- (NSDictionary<NSString *, NSString *> *)constantsToExport {
  return @{ @"BEACON_SIGHTED": kBeaconSighted,
            @"BEACON_DEPARTED": kBeaconDeparted,
            };
}

- (NSArray<NSString *> *)supportedEvents {
  return @[kBeaconSighted,
           kBeaconDeparted
           ];
}

- (void)startObserving {
  for (NSString *event in [self supportedEvents]) {
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(handleNotification:)
                                                 name:event
                                               object:nil];
  }
}

- (void)stopObserving {
  [[NSNotificationCenter defaultCenter] removeObserver:self];
}

# pragma mark Public

+ (BOOL)application:(UIApplication *)application didSightBeacon:(NSString *)beaconID {
  [self postNotificationName:kBeaconSighted withPayload:beaconID];
  return YES;
}

+ (BOOL)application:(UIApplication *)application didDepartBeacon:(NSString *)beaconID {
  [self postNotificationName:kBeaconDeparted withPayload:beaconID];
  return YES;
}

# pragma mark Private

+ (void)postNotificationName:(NSString *)name withPayload:(NSObject *)object {
  NSDictionary<NSString *, id> *payload = @{@"payload": object};
  
  [[NSNotificationCenter defaultCenter] postNotificationName:name
                                                      object:self
                                                    userInfo:payload];
}

- (void)handleNotification:(NSNotification *)notification {
  [self sendEventWithName:notification.name body:notification.userInfo];
}

@end

Where declared variable "kBeaconSightingNotification" ?

What's kBeaconSightingNotification?

@byk04712 @paalex Sorry, "kBeaconSightingNotification" was a typo. It should have been "kSightedBeacon". I've updated the gist to correct the typo and to show how to support multiple notifications with a single class.