Listener methods
This is the collection of listener methods within the Checkpoints interface. There are only three listener methods, addCheckpointIdsListener, addCheckpointListener, and delListener.
addCheckpointIdsListener
The addCheckpointIdsListener method registers a listener function with the Checkpoints object that will be called whenever its set of checkpoints changes.
addCheckpointListener
The addCheckpointListener method registers a listener function with the Checkpoints object that will be called whenever the label of a checkpoint changes.
delListener
The delListener method removes a listener that was previously added to the Checkpoints object.