Observer/pubsub demo

Quick demo of the observer / pubsub pattern.

The scenario here is a publisher notifiying its subscribers of events. Subscribers have callbacks registered with the publisher for particular event types. Each subscriber’s callback is called when the publisher emits the associated event.

# create instances
pub = new Pub('Acme Media')   # publisher
bob = new Sub('Bob')          # subscribers
ann = new Sub('Ann')

# set up subscriptions
pub
  .on('vogue', ann.read)
  .on('glee', ann.watch)
  .on('glee', bob.watch)

# notify subscribers
pub
  .emit('glee')
  .emit('vogue')

Expected output:

Acme Media notifies its subscribers of glee:
 * Ann is now watching glee
 * Bob is now watching glee

Acme Media notifies its subscribers of glee:
 * Ann is now reading vogue