string  topic,  object  context,  function  callback  ); amplify.subscribe(  string  topic,  function  callback,  number  priority); amplify.subscribe(  string  topic,  object  context,  function  callback,                                        number  priority); • topic: Name of the message to subscribe to. • [context]: What this will be when the callback is invoked. • callback: Function to invoke when the message is published. • [priority]: Priority relative to other subscriptions for the same message.