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FileSystemSyncAccessHandle: flush() method

files/en-us/web/api/filesystemsyncaccesshandle/flush/index.md

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

The flush() method of the {{domxref("FileSystemSyncAccessHandle")}} interface persists any changes made to the file associated with the handle via the {{domxref('FileSystemSyncAccessHandle.write', 'write()')}} method to disk.

Bear in mind that you only need to call this method if you need the changes committed to disk at a specific time, otherwise you can leave the underlying operating system to handle this when it sees fit, which should be OK in most cases.

[!NOTE] In earlier versions of the spec, {{domxref("FileSystemSyncAccessHandle.close()", "close()")}}, 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.

Syntax

js-nolint
flush()

Parameters

None.

Return value

None ({{jsxref('undefined')}}).

Exceptions

  • InvalidStateError {{domxref("DOMException")}}
    • : Thrown if the associated access handle is already closed.

Examples

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 {{jsxref("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.
js
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();
};

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also