How to use the sharedb.PubSub function in sharedb

var redis = require('redis');
var PubSub = require('sharedb').PubSub;

// Redis pubsub driver for ShareDB.
//
// The redis driver requires two redis clients (a single redis client can't do
// both pubsub and normal messaging). These clients will be created
// automatically if you don't provide them.
function RedisPubSub(options) {
  if (!(this instanceof RedisPubSub)) return new RedisPubSub(options);
  PubSub.call(this, options);
  options || (options = {});

  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