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FileSystemSyncAccessHandle: truncate() method

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

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

The truncate() method of the {{domxref("FileSystemSyncAccessHandle")}} interface resizes the file associated with the handle to a specified number of bytes.

[!NOTE] In earlier versions of the spec, {{domxref("FileSystemSyncAccessHandle.close()", "close()")}}, {{domxref("FileSystemSyncAccessHandle.flush()", "flush()")}}, {{domxref("FileSystemSyncAccessHandle.getSize()", "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-nolint
truncate(newSize)

Parameters

  • newSize
    • : The number of bytes to resize the file to.

Return value

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

Exceptions

  • InvalidStateError {{domxref("DOMException")}}
    • : Thrown if the associated access handle is already closed, or if the modification of the file's binary data otherwise fails.
  • {{domxref("QuotaExceededError")}}
    • : Thrown if the newSize is larger than the original size of the file, and exceeds the browser's storage quota.
  • {{jsxref("TypeError")}}
    • : Thrown if the underlying file system does not support setting the file size to the new size.

Examples

js
async function truncateFile() {
  // 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();

  // Truncate the file to 0 bytes
  accessHandle.truncate(0);

  // Persist changes to disk.
  accessHandle.flush();

  // Always close FileSystemSyncAccessHandle if done.
  accessHandle.close();
}

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also