getDirectory()

onmessage = async (e) => {
  // Retrieve message sent to work from main script
  const message = e.data;

  // Get handle to draft file
  const root = await navigator.storage.getDirectory();
  const draftHandle = await root.getFileHandle("draft.txt", { create: true });
  // Get sync access handle
  const accessHandle = await draftHandle.createSyncAccessHandle();

  // Get size of the file.
  const fileSize = accessHandle.getSize();
  // Read file content to a buffer.
  const buffer = new DataView(new ArrayBuffer(fileSize));
  const readBuffer = accessHandle.read(buffer, { at: 0 });

  // Write the message to the end of the file.
  const encoder = new TextEncoder();
  const encodedMessage = encoder.encode(message);
  const writeBuffer = accessHandle.write(encodedMessage, { at: readBuffer });

  // Persist changes to disk.
  accessHandle.flush();

  // Always close FileSystemSyncAccessHandle if done.
  accessHandle.close();
};