FileSystemDirectoryHandle: метод resolve()

resolve(possibleDescendant)

async function returnPathDirectories(directoryHandle) {
  // Get a file handle by showing a file picker:
  const [handle] = await self.showOpenFilePicker();
  if (!handle) {
    // User cancelled, or otherwise failed to open a file.
    return;
  }

  // Check if handle exists inside our directory handle
  const relativePaths = await directoryHandle.resolve(handle);

  if (relativePaths === null) {
    // Not inside directory handle
  } else {
    // relativePath is an array of names, giving the relative path
    for (const name of relativePaths) {
      // log each entry
      console.log(name);
    }
  }
}