Alias of filehandle.writeFile().
When operating on file handles, the mode cannot be changed from what it was set
to with fsPromises.open(). Therefore, this is equivalent to filehandle.writeFile().
Optionaloptions: BufferEncoding | ObjectEncodingOptions & AbortableFulfills with undefined upon success.
Changes the ownership of the file. A wrapper for chown(2).
The file's new owner's user id.
The file's new group's group id.
Fulfills with undefined upon success.
Closes the file handle after waiting for any pending operation on the handle to complete.
import { open } from 'node:fs/promises';
let filehandle;
try {
filehandle = await open('thefile.txt', 'r');
} finally {
await filehandle?.close();
}
Fulfills with undefined upon success.
Unlike the 16 KiB default highWaterMark for a stream.Readable, the stream
returned by this method has a default highWaterMark of 64 KiB.
options can include start and end values to read a range of bytes from
the file instead of the entire file. Both start and end are inclusive and
start counting at 0, allowed values are in the
[0, Number.MAX_SAFE_INTEGER] range. If start is
omitted or undefined, filehandle.createReadStream() reads sequentially from
the current file position. The encoding can be any one of those accepted by Buffer.
If the FileHandle points to a character device that only supports blocking
reads (such as keyboard or sound card), read operations do not finish until data
is available. This can prevent the process from exiting and the stream from
closing naturally.
By default, the stream will emit a 'close' event after it has been
destroyed. Set the emitClose option to false to change this behavior.
import { open } from 'node:fs/promises';
const fd = await open('/dev/input/event0');
// Create a stream from some character device.
const stream = fd.createReadStream();
setTimeout(() => {
stream.close(); // This may not close the stream.
// Artificially marking end-of-stream, as if the underlying resource had
// indicated end-of-file by itself, allows the stream to close.
// This does not cancel pending read operations, and if there is such an
// operation, the process may still not be able to exit successfully
// until it finishes.
stream.push(null);
stream.read(0);
}, 100);
If autoClose is false, then the file descriptor won't be closed, even if
there's an error. It is the application's responsibility to close it and make
sure there's no file descriptor leak. If autoClose is set to true (default
behavior), on 'error' or 'end' the file descriptor will be closed
automatically.
An example to read the last 10 bytes of a file which is 100 bytes long:
import { open } from 'node:fs/promises';
const fd = await open('sample.txt');
fd.createReadStream({ start: 90, end: 99 });
Optionaloptions: CreateReadStreamOptionsoptions may also include a start option to allow writing data at some
position past the beginning of the file, allowed values are in the
[0, Number.MAX_SAFE_INTEGER] range. Modifying a file rather than
replacing it may require the flags open option to be set to r+ rather than
the default r. The encoding can be any one of those accepted by Buffer.
If autoClose is set to true (default behavior) on 'error' or 'finish' the file descriptor will be closed automatically. If autoClose is false,
then the file descriptor won't be closed, even if there's an error.
It is the application's responsibility to close it and make sure there's no
file descriptor leak.
By default, the stream will emit a 'close' event after it has been
destroyed. Set the emitClose option to false to change this behavior.
Optionaloptions: CreateWriteStreamOptionsForces all currently queued I/O operations associated with the file to the
operating system's synchronized I/O completion state. Refer to the POSIX fdatasync(2) documentation for details.
Unlike filehandle.sync this method does not flush modified metadata.
Fulfills with undefined upon success.
Reads data from the file and stores that in the given buffer.
If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero.
A buffer that will be filled with the file data read.
Optionaloffset: numberThe location in the buffer at which to start filling.
Optionallength: numberThe number of bytes to read.
Optionalposition: numberThe location where to begin reading data from the file. If null, data will be read from the current file position, and the position will be updated. If position is an
integer, the current file position will remain unchanged.
Fulfills upon success with an object with two properties:
Optionaloptions: FileReadOptions<T>Optionaloptions: FileReadOptions<T>ExperimentalReturns a byte-oriented ReadableStream that may be used to read the file's
contents.
An error will be thrown if this method is called more than once or is called
after the FileHandle is closed or closing.
import {
open,
} from 'node:fs/promises';
const file = await open('./some/file/to/read');
for await (const chunk of file.readableWebStream())
console.log(chunk);
await file.close();
While the ReadableStream will read the file to completion, it will not
close the FileHandle automatically. User code must still call thefileHandle.close() method.
Asynchronously reads the entire contents of a file.
If options is a string, then it specifies the encoding.
The FileHandle has to support reading.
If one or more filehandle.read() calls are made on a file handle and then a filehandle.readFile() call is made, the data will be read from the current
position till the end of the file. It doesn't always read from the beginning
of the file.
Optionaloptions: { encoding?: null } & AbortableFulfills upon a successful read with the contents of the file. If no encoding is specified (using options.encoding), the data is returned as a {Buffer} object. Otherwise, the
data will be a string.
Asynchronously reads the entire contents of a file. The underlying file will not be closed automatically.
The FileHandle must have been opened for reading.
Asynchronously reads the entire contents of a file. The underlying file will not be closed automatically.
The FileHandle must have been opened for reading.
Optionaloptions: BufferEncoding | ObjectEncodingOptions & AbortableConvenience method to create a readline interface and stream over the file.
See filehandle.createReadStream() for the options.
import { open } from 'node:fs/promises';
const file = await open('./some/file/to/read');
for await (const line of file.readLines()) {
console.log(line);
}
Optionaloptions: CreateReadStreamOptionsRead from a file and write to an array of ArrayBufferView s
Optionalposition: numberThe offset from the beginning of the file where the data should be read from. If position is not a number, the data will be read from the current position.
Fulfills upon success an object containing two properties:
Optionalopts: StatOptions & { bigint?: false }Fulfills with an {fs.Stats} for the file.
Optionalopts: StatOptionsRequest that all data for the open file descriptor is flushed to the storage
device. The specific implementation is operating system and device specific.
Refer to the POSIX fsync(2) documentation for more detail.
Fulfills with undefined upon success.
Truncates the file.
If the file was larger than len bytes, only the first len bytes will be
retained in the file.
The following example retains only the first four bytes of the file:
import { open } from 'node:fs/promises';
let filehandle = null;
try {
filehandle = await open('temp.txt', 'r+');
await filehandle.truncate(4);
} finally {
await filehandle?.close();
}
If the file previously was shorter than len bytes, it is extended, and the
extended part is filled with null bytes ('\0'):
If len is negative then 0 will be used.
Optionallen: numberFulfills with undefined upon success.
Write buffer to the file.
The promise is fulfilled with an object containing two properties:
It is unsafe to use filehandle.write() multiple times on the same file
without waiting for the promise to be fulfilled (or rejected). For this
scenario, use filehandle.createWriteStream().
On Linux, positional writes do not work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
Optionaloffset: numberThe start position from within buffer where the data to write begins.
Optionallength: numberThe number of bytes from buffer to write.
Optionalposition: numberThe offset from the beginning of the file where the data from buffer should be written. If position is not a number, the data will be written at the current
position. See the POSIX pwrite(2) documentation for more detail.
Optionalposition: numberOptionalencoding: BufferEncodingAsynchronously writes data to a file, replacing the file if it already exists. data can be a string, a buffer, an
AsyncIterable, or an
Iterable object.
The promise is fulfilled with no arguments upon success.
If options is a string, then it specifies the encoding.
The FileHandle has to support writing.
It is unsafe to use filehandle.writeFile() multiple times on the same file
without waiting for the promise to be fulfilled (or rejected).
If one or more filehandle.write() calls are made on a file handle and then afilehandle.writeFile() call is made, the data will be written from the
current position till the end of the file. It doesn't always write from the
beginning of the file.
Optionaloptions: BufferEncoding | ObjectEncodingOptions & AbortableWrite an array of ArrayBufferView s to the file.
The promise is fulfilled with an object containing a two properties:
It is unsafe to call writev() multiple times on the same file without waiting
for the promise to be fulfilled (or rejected).
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
Optionalposition: numberThe offset from the beginning of the file where the data from buffers should be written. If position is not a number, the data will be written at the current
position.
The numeric file descriptor managed by the {FileHandle} object.