code: function promisifyIE11Op(keyObj, err) {
    if (typeof keyObj.then !== 'function') { // IE11 KeyOperation
      return new Promise(function(resolve, reject) {
        keyObj.onerror = function () {
          reject(new Error(err));
        };
        keyObj.oncomplete = function (e) {
          resolve(e.target.result);
        };
      });
    }
    return keyObj;
  }
docs: Helper for IE11 KeyOperation objects