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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.

Note: In earlier versions of the spec, close(), flush(), getSize(), and 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

getSize()

Parameters

None.

Return value

A number representing the size of the file in bytes.

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();
};

Specifications

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
getSize 102 102 111 No 88 15.2 109 109 111 74 15.2 21.0
sync_version 108 108 111 No 94 16.4 109 109 111 74 16.4 21.0

See also

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/FileSystemSyncAccessHandle/getSize