Future.microtask(dynamic computation())

Creates a future containing the result of calling computation asynchronously with scheduleMicrotask.

If executing computation throws, the returned future is completed with the thrown error.

If calling computation returns a Future, completion of the created future will wait until the returned future completes, and will then complete with the same result.

If calling computation returns a non-future value, the returned future is completed with that value.

Source 

factory Future.microtask(computation()) {
  _Future<T> result = new _Future<T>();
  scheduleMicrotask(() {
    try {
      result._complete(computation());
    } catch (e, s) {
      _completeWithErrorCallback(result, e, s);
    }
  });
  return result;
}