docs: function(storeName, key, cb) {
      if (!Array.isArray(key)) {
        key = [key];
      }
  
      var result = [];
      var transaction = this.transaction(storeName, MODE.READ_WRITE, result, cb);
      var store = this.store(storeName, transaction, cb);
      var _del = function(key) {
        var request;
        try {
          request = store.delete(key);
        } catch (err) {
          if (isFunction(cb)) return cb(err);
        }
        request.onsuccess = function(event) {
          result.push(event.target.result);
        };
        request.onerror = function(event) {
          if (isFunction(cb)) return cb(event.target.error);
        };
      };
      for (var i = 0, l = key.length; i < l; i++) {
        _del(key[i]);
      }
    }