How to use the sharedb.PubSub.prototype function in sharedb

this.client = options.client || redis.createClient(options);

  // Redis doesn't allow the same connection to both listen to channels and do
  // operations. Make an extra redis connection for subscribing with the same
  // options if not provided
  this.observer = options.observer || redis.createClient(this.client.options);

  var pubsub = this;
  this.observer.on('message', function(channel, message) {
    var data = JSON.parse(message);
    pubsub._emit(channel, data);
  });
}
module.exports = RedisPubSub;

RedisPubSub.prototype = Object.create(PubSub.prototype);

RedisPubSub.prototype.close = function(callback) {
  if (!callback) {
    callback = function(err) {
      if (err) throw err;
    };
  }
  var pubsub = this;
  PubSub.prototype.close.call(this, function(err) {
    if (err) return callback(err);
    pubsub.client.quit(function(err) {
      if (err) return callback(err);
      pubsub.observer.quit(callback);
    });
  });
};

RedisPubSub.prototype.close = function(callback) {
  if (!callback) {
    callback = function(err) {
      if (err) throw err;
    };
  }
  var pubsub = this;
  PubSub.prototype.close.call(this, function(err) {
    if (err) return callback(err);
    pubsub.client.quit(function(err) {
      if (err) return callback(err);
      pubsub.observer.quit(callback);
    });
  });
};