possible rephrase to:

"...in order to invoke its +register+ function which will register the device with CGM. Notice, that the function apart from the usual success/failure callbacks, require as parameter the Google Sender ID and the callback function name which would be invoked by the PushPlugin to pass along the notification events. Here we use the 'onNotification' function name that we defined earlier."

and the code should be changed to:
 pushNotification.register(successCallback, errorCallback, {"senderID": "e.g. 4815162342", "ecb": "onNotification"})