FileSystemSyncAccessHandle: getSize() method

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

The getSize() method of the FileSystemSyncAccessHandle interface returns the size of the file associated with the handle in bytes.

Syntax

js

getSize()

Parameters

None.

Return value

A Promise which resolves to a number representing the number of bytes in the file.

Exceptions

InvalidStateError 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 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();
};

Note: In earlier versions of the spec, close(), flush(), getSize(), and truncate() were wrongly specified as asynchronous methods. This has now been amended, but some browsers still support the asynchronous versions.

Specifications

Specification
File System Standard
# api-filesystemsyncaccesshandle-getsize

Browser compatibility

BCD tables only load in the browser

See also