arangojs: How to handle connection errors ?

Seems like Database() do not have any error callbacks and do not have any of the connected()/state() functions. How to know that connection was successful/unsuccessful ? For example doing connection to the unresolved host will not return any errors at the following simple example:

var db_config = {
  url: 'http://root:@some.unknown.host:8529',
  retryConnection: true
};
var db = new arangodb.Database(db_config);
db.listCollections(/* false */)
 .then(collections => {
   for (var i in collections) {
     console.log(collections[i]);
   }
}, err => {
  console.log('listCollections error: ' + err);
});