callback format

var db = new Db('local', new Server('localhost', 27017));
module.exports.dbs = exports.dbs;

exports.dbs = function(callback){
  db.open(function(err, db){
    if(err) callback(err);
    var adminDb = db.admin();
    adminDb.listDatabases(function(err, dbs){
      if(err) callback(err);
      db.close();
      callback(null, dbs);
    })
  })
}