code: function IDBIndex(store, indexProperties) {
          this.objectStore = store;
          this.name = indexProperties.columnName;
          this.keyPath = indexProperties.keyPath;
          this.multiEntry = indexProperties.optionalParams && indexProperties.optionalParams.multiEntry;
          this.unique = indexProperties.optionalParams && indexProperties.optionalParams.unique;
          this.__deleted = !!indexProperties.__deleted;
      }
docs: IDB Index
  http://www.w3.org/TR/IndexedDB/#idl-def-IDBIndex
  @param {IDBObjectStore} store
  @param {IDBIndexProperties} indexProperties
  @constructor