FileSystemWritableFileStream: write() method
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The write()
method of the FileSystemWritableFileStream
interface writes content into the file the method is called on, at the current file cursor offset.
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. This method can also be used to seek to a byte point within the stream and truncate to modify the total bytes the file contains.
Syntax
js
write(data)
Parameters
data
-
Can be either the file data to write, in the form of an
ArrayBuffer
, aTypedArray
, aDataView
, aBlob
, aString
object, or a string literal. Or an object containing the following properties:type
-
A string that is one of the following:
"write"
,"seek"
, or"truncate"
. data
-
The file data to write. Can be an
ArrayBuffer
, aTypedArray
, aDataView
, aBlob
, aString
object, or a string literal. This property is required iftype
is set towrite
. position
-
The byte position the current file cursor should move to if type
seek
is used. Can also be set with iftype
iswrite
, in which case the write will start at the position. size
-
An unsigned long value representing the amount of bytes the stream should contain. This property is required if
type
is set totruncate
.
Return value
Promise
which returns undefined.
Exceptions
NotAllowedError
DOMException
-
Returned if
PermissionStatus
is not granted. TypeError
-
Returned if data is undefined, or if
position
orsize
aren't valid. InvalidStateError
DOMException
-
Returned if the
position
is set and larger than the bytes available.
Examples
This asynchronous function opens the 'Save File' picker, which returns a FileSystemFileHandle
once a file is selected.
From which a writable stream is then created using the FileSystemFileHandle.createWritable()
method.
A user defined Blob
is then written to the stream which is subsequently closed.
js
async function saveFile() {
// 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(imgBlob);
// close the file and write the contents to disk.
await writableStream.close();
}
The following show different examples of options that can be passed into the write()
method.
js
// just pass in the data (no options)
writableStream.write(data);
// writes the data to the stream from the determined position
writableStream.write({ type: "write", position, data });
// updates the current file cursor offset to the position specified
writableStream.write({ type: "seek", position });
// resizes the file to be size bytes long
writableStream.write({ type: "truncate", size });
Specifications
Specification |
---|
File System Standard # api-filesystemwritablefilestream-write |
Browser compatibility
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