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

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The truncate() method of the FileSystemWritableFileStream interface resizes the file associated with the stream to be the specified size in bytes.

If the size specified is larger than the current file size this pads the file with null bytes, otherwise it truncates the file.

The file cursor is also updated when truncate() is called. If the offset is smaller than the size, it remains unchanged. If the offset is larger than size, the offset is set to that size. This ensures that subsequent writes do not error.

No changes are written to the actual file on disk until the stream has been closed. Changes are typically written to a temporary file instead.





An unsigned long of the amount of bytes to resize the stream to.

Return value

A Promise which returns undefined.


NotAllowedError DOMException

If the PermissionState is not 'granted'.


If the size is undefined or not an unsigned long.


// todo


File System Standard
# api-filesystemwritablefilestream-truncate

Browser compatibility

BCD tables only load in the browser

See also