code: function MongoStore(uri, options) {
          var self = this;
  
          this.options = options || (options = {});
          options.collectionName = options.collectionName || 'sessions';
          // 1 day
          options.ttl = options.ttl || 24 * 60 * 60 * 1000;
          // 60 s
          options.cleanupInterval = options.cleanupInterval || 60 * 1000;
          options.server = options.server || {};
          options.server.auto_reconnect = options.server.auto_reconnect != null ? options.server.auto_reconnect : true;
  
          this._error = function(err) {
              if (err) { self.emit('error', err); }
          };
  
          // It's a Db instance.
          if (uri.collection) {
              this.db = uri;
              this._setup();
          } else {
              MongoClient.connect(uri, options, function(err, db) {
                  if (err) { return self._error(err); }
                  self.db = db;
                  self._setup();
              });
          }
      }
docs: Initialize a new `MongoStore`.
  
  @api public