GMaps.geolocate supports 4 functions:

• success (required): fires when geolocation has been successful
• error (required): fires when geolocation has not been done
• not_supported (required): fires when geolocation is not supported by the browser
• always (optional): fires always after every scenario described above.

You can define either address or lat and lng. Also, you must define callback, which will use results of geocoding and status.