code: function removeItem(key, callback) {
          var self = this;
  
          // Cast the key to a string, as that's all we can set as a key.
          if (typeof key !== 'string') {
              window.console.warn(key +
                                  ' used as a key, but it is not a string.');
              key = String(key);
          }
  
          var promise = new Promise(function(resolve, reject) {
              self.ready().then(function() {
                  var dbInfo = self._dbInfo;
                  localStorage.removeItem(dbInfo.keyPrefix + key);
  
                  resolve();
              })["catch"](reject);
          });
  
          executeCallback(promise, callback);
          return promise;
      }
docs: Remove an item from the store, nice and simple.