docs: function(storeName, cb) {
      var result;
      var transaction = this.transaction(storeName, MODE.READ_ONLY, result, cb);
      var store = this.store(storeName, transaction, cb);
      var request;
      try {
        request = store.count();
      } catch (err) {
        if (isFunction(cb)) return cb(err);
      }
      request.onsuccess = function(event) {
        result = event.target.result;
      };
      request.onerror = function(event) {
        if (isFunction(cb)) return cb(event.target.error);
      };
    }