StorageManager: getDirectory() method

{{securecontext_header}}{{APIRef("File System API")}} {{AvailableInWorkers}}

The getDirectory() method of the {{domxref("StorageManager")}} interface is used to obtain a reference to a {{domxref("FileSystemDirectoryHandle")}} object allowing access to a directory and its contents, stored in the origin private file system (OPFS).

Syntax

getDirectory()

Parameters

None.

Return value

A {{jsxref('Promise')}} that fulfills with a {{domxref("FileSystemDirectoryHandle")}} object.

Exceptions

• SecurityError {{domxref("DOMException")}}
  • : Thrown if the browser is not able to map the requested directory to the local OPFS, for example due to storage or memory constraints. Also thrown in some browsers if getDirectory() is called in private browsing mode.
• UnknownError {{domxref("DOMException")}}
  • : Thrown in some browsers if getDirectory() is called in private browsing mode.

Examples

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

1. Gets a {{domxref("FileSystemDirectoryHandle")}} representing the root of the OPFS using getDirectory(), storing it in the root variable.
2. Gets a file handle using {{domxref("FileSystemDirectoryHandle.getFileHandle()")}}.
3. Creates a synchronous file access handle using {{domxref("FileSystemFileHandle.createSyncAccessHandle()")}}.
4. Gets the size of the file and creates an {{jsxref("ArrayBuffer")}} to contain it.
5. Reads and writes to the file.
6. Persists the changes to disk and closes the synchronous 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();
};

[!NOTE] In earlier versions of the spec, {{domxref("FileSystemSyncAccessHandle.close()", "close()")}}, {{domxref("FileSystemSyncAccessHandle.flush()", "flush()")}}, {{domxref("FileSystemSyncAccessHandle.getSize()", "getSize()")}}, and {{domxref("FileSystemSyncAccessHandle.truncate()", "truncate()")}} were wrongly specified as asynchronous methods, and older versions of some browsers implement them in this way. However, all current browsers that support these methods implement them as synchronous methods.

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{domxref("StorageManager")}}
• {{domxref("Navigator.storage")}}
• {{domxref("WorkerNavigator.storage")}}
• {{domxref("FileSystemDirectoryHandle")}}