code: function getThisValueAndInvoke (callback) {
              return callback(currentThis !== undefined && currentThis !== null ?
                  (typeof currentThis === 'object' ? currentThis : currentThis.valueOf()) : currentThis
              );
          }
docs: Retrieves the last item from the 'thisPointerStack' and invokes the provided callback with it.
  @param {Function} callback The callback to be invoked with the current 'this' value.
  @return The result of the invocation of the callback.