The write() method of the FileSystemSyncAccessHandle interface writes the content of a specified buffer to the file associated with the handle, optionally at a given offset.
Files within the origin private file system are not visible to end-users, therefore are not subject to the same security checks as methods running on files within the user-visible file system. As a result, writes performed using FileSystemSyncAccessHandle.write() are much more performant. This makes them suitable for significant, large-scale file updates such as SQLite database modifications.
buffer-
An ArrayBuffer or ArrayBufferView (such as a DataView) representing the buffer to be written to the file.
-
options Optional
-
An options object containing the following properties:
at-
A number representing the offset in bytes from the start of the file that the buffer should be written at.
Note: You cannot directly manipulate the contents of an ArrayBuffer. Instead, you create a typed array object like an Int8Array or a DataView object, which represents the buffer in a specific format, and use that to read and write the contents of the buffer.
A number representing the number of bytes written to the file.
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.
onmessage = async (e) => {
const message = e.data;
const root = await navigator.storage.getDirectory();
const draftHandle = await root.getFileHandle("draft.txt", { create: true });
const accessHandle = await draftHandle.createSyncAccessHandle();
const fileSize = accessHandle.getSize();
const buffer = new DataView(new ArrayBuffer(fileSize));
const readBuffer = accessHandle.read(buffer, { at: 0 });
const encoder = new TextEncoder();
const encodedMessage = encoder.encode(message);
const writeBuffer = accessHandle.write(encodedMessage, { at: readBuffer });
accessHandle.flush();
accessHandle.close();
};
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.