Theseek() method of theFileSystemWritableFileStream interface updates the current file cursor offset to the position (in bytes) specified when calling the method.

Syntax

seek(position)

Parameters

position

A number specifying the byte position from the beginning of the file.

Return value

APromise that returnsundefined.

Exceptions

NotAllowedErrorDOMException

Thrown ifPermissionStatus.state is notgranted.

TypeError

Thrown ifposition is not a number or not defined.

Examples

The following asynchronous function opens the 'Save File' picker, which returns aFileSystemFileHandle once a file is selected. From this, a writable stream is created using theFileSystemFileHandle.createWritable() method.

Next, we write to the stream:

1. A text string is written to the stream.
2. Theseek() method is used to put the cursor at the start of the stream.
3. A second text string is written to the start of the stream, overwriting the first write.

The stream is then closed.

async function saveFile() {  try {    // create a new handle    const newHandle = await window.showSaveFilePicker();    // create a FileSystemWritableFileStream to write to    const writableStream = await newHandle.createWritable();    // write our file    await writableStream.write("My first file content");    await writableStream.seek(0);    await writableStream.write("My second file content");    // close the file and write the contents to disk.    await writableStream.close();  } catch (err) {    console.error(err.name, err.message);  }}

If you run the above function and then open the resulting file created on disk, you should see the text "My second file content".

Specifications

Browser compatibility

See also

• File System API
• The File System Access API: simplifying access to local files