code: function MongoStore(options) {
          options = options || {};
  
          for (var property in defaultOptions) {
              if (defaultOptions.hasOwnProperty(property)) {
                  if (!options.hasOwnProperty(property) || (typeof defaultOptions[property] !== typeof options[property]))
                      options[property] = defaultOptions[property];
              }
          }
  
          Store.call(this, options.store);
  
          var dbProperties = ["name", "prefix", "servers", "credentials", "URLParam", "extraParam"];
          var dbPropertiesLen = dbProperties.length;
          var dbOptions = {};
          for (var i = 0; i < dbPropertiesLen; i++)
              dbOptions[dbProperties[i]] = options[dbProperties[i]];
  
          this.mongo = new Mongo(dbOptions);
          this.mongo.ensureIndex(options.collection, {expires: 1}, {expireAfterSeconds: 0}, function (err, result) {
              if (err)
                  throw new Error('Error setting TTL index on collection : ' + options.collection + ' <' + err + '>');
          });
  
          this._options = {
              "collection": options.collection,
              "stringify": options.stringify,
              "expireAfter": options.expireAfter
          };
      }
docs: Initialize MongoStore with the given `options`.
  
  @param {Object} options