FileSystemSyncAccessHandle

None.

close()

Closes an open synchronous file handle, disabling any further operations on it and releasing the exclusive lock previously put on the file associated with the file handle.

flush()

Persists any changes made to the file associated with the handle via the write() method to disk.

getSize()

Returns the size of the file associated with the handle in bytes.

read()

Reads the content of the file associated with the handle into a specified buffer, optionally at a given offset.

truncate()

Resizes the file associated with the handle to a specified number of bytes.

write()

Writes the content of a specified buffer to the file associated with the handle, optionally at a given offset.

The following asynchronous event handler function is contained inside a Web Worker. On receiving a message from the main thread it:

• Creates a synchronous file access handle.
• Gets the size of the file and creates an ArrayBuffer to contain it.
• Reads the file contents into the buffer.
• Encodes the message and writes it to the end of the file.
• Persists the changes to disk and closes the access handle.

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();
};

• File System Access API
• The File System Access API: simplifying access to local files