See #17798
}
    let alternate = fiber.alternate;
    if (!alternate) {
       I
      const state = isFiberMountedImpl(fiber);
      if (state === UNMOUNTED) {
        throw Error('Unable to find node on an unmounted component.');
      }
      if (state === MOUNTING) {
        return null;
      }
      return fiber;
    }
     I
     t
     s
    let a: Fiber = fiber;
    let b: Fiber = alternate;
    while (true) {
      let parentA = a.return;
      if (parentA === null) {
         W
        break;
      }
      let parentB = parentA.alternate;
      if (parentB === null) {
         T
         h
         i
         o