FileSystemWritableFileStream: seek() method
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
Note: This feature is available in Web Workers.
The seek()
method of the FileSystemWritableFileStream
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
A Promise
that returns undefined
.
Exceptions
NotAllowedError
DOMException
-
Thrown if
PermissionStatus.state
is notgranted
. TypeError
-
Thrown if
position
is not a number or not defined.
Examples
The following asynchronous function opens the 'Save File' picker, which returns a FileSystemFileHandle
once a file is selected. From this, a writable stream is created using the FileSystemFileHandle.createWritable()
method.
Next, we write to the stream:
- A text string is written to the stream.
- The
seek()
method is used to put the cursor at the start of the stream. - 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
Specification |
---|
File System Standard # api-filesystemwritablefilestream-seek |
Browser compatibility
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