@caido/quickjs-types / llrt/fs / fs/promises

fs/promises

Classes

FileHandle

Constructors

Constructor

new FileHandle(): FileHandle

Returns

FileHandle

Properties

fd

readonly fd: number

The numeric file descriptor managed by the {FileHandle} object.

Methods

chmod()

chmod(mode: number): Promise<void>

Modifies the permissions on the file. See chmod(2).

Parameters

Parameter	Type	Description
mode	number	the file mode bit mask.

Returns

Promise<void>

Fulfills with undefined upon success.

chown()

chown(uid: number, gid: number): Promise<void>

Changes the ownership of the file. A wrapper for chown(2).

Parameters

Parameter	Type	Description
uid	number	The file's new owner's user id.
gid	number	The file's new group's group id.

Returns

Promise<void>

Fulfills with undefined upon success.

close()

close(): Promise<void>

Closes the file handle after waiting for any pending operation on the handle to complete.

import { open } from 'fs/promises';

let filehandle;
try {
  filehandle = await open('thefile.txt', 'r');
} finally {
  await filehandle?.close();
}

Returns

Promise<void>

Fulfills with undefined upon success.

datasync()

datasync(): Promise<void>

Forces 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.

Returns

Promise<void>

Fulfills with undefined upon success.

read()

Call Signature

read<T>(buffer: T, offset?: number | null, length?: number | null, position?: number | null): Promise<FileReadResult<T>>

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.

Type Parameters

Type Parameter
T extends ArrayBufferView

Parameters

Parameter	Type	Description
buffer	T	A buffer that will be filled with the file data read.
offset?	number | null	The location in the buffer at which to start filling.
length?	number | null	The number of bytes to read.
position?	number | null	The 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.

Returns

Promise<FileReadResult<T>>

Fulfills upon success with an object with two properties: bytesRead and buffer

Call Signature

read<T>(buffer: T, options?: FileReadOptions<T>): Promise<FileReadResult<T>>

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.

Type Parameters

Type Parameter	Default type
T extends ArrayBufferView	Buffer

Parameters

Parameter	Type	Description
buffer	T	A buffer that will be filled with the file data read.
options?	FileReadOptions<T>	-

Returns

Promise<FileReadResult<T>>

Fulfills upon success with an object with two properties: bytesRead and buffer

Call Signature

read<T>(options?: FileReadOptions<T>): Promise<FileReadResult<T>>

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.

Type Parameters

Type Parameter	Default type
T extends ArrayBufferView	Buffer

Parameters

Parameter	Type
options?	FileReadOptions<T>

Returns

Promise<FileReadResult<T>>

Fulfills upon success with an object with two properties: bytesRead and buffer

readFile()

Call Signature

readFile(options?: { encoding?: null; } | null): Promise<Buffer>

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.

Parameters

Parameter	Type
options?	{ encoding?: null; } | null

Returns

Promise<Buffer>

Fulfills 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.

Call Signature

readFile(options: BufferEncoding | { encoding: BufferEncoding; }): Promise<string>

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.

Parameters

Parameter	Type
options	BufferEncoding | { encoding: BufferEncoding; }

Returns

Promise<string>

Fulfills 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.

stat()

stat(): Promise<Stats>

Get {FileHandle} status.

Returns

Promise<Stats>

Fulfills with the {fs.Stats} object.

sync()

sync(): Promise<void>

Request 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.

Returns

Promise<void>

Fulfills with undefined upon success.

truncate()

truncate(len?: number): Promise<void>

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 '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'):

Parameters

Parameter	Type	Description
len?	number

Returns

Promise<void>

Fulfills with undefined upon success.

write()

Call Signature

write<TBuffer>(buffer: TBuffer, offset?: number | null, length?: number | null, position?: number | null): Promise<{ buffer: TBuffer; bytesWritten: number; }>

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.

Type Parameters

Type Parameter
TBuffer extends ArrayBufferView

Parameters

Parameter	Type	Description
buffer	TBuffer	-
offset?	number | null	The start position from within buffer where the data to write begins.
length?	number | null	The number of bytes from buffer to write.
position?	number | null	The 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.

Returns

Promise<{ buffer: TBuffer; bytesWritten: number; }>

Call Signature

write<TBuffer>(buffer: TBuffer, options?: { length?: number | null; offset?: number | null; position?: number | null; } | null): Promise<{ buffer: TBuffer; bytesWritten: number; }>

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.

Type Parameters

Type Parameter
TBuffer extends ArrayBufferView

Parameters

Parameter	Type
buffer	TBuffer
options?	{ length?: number | null; offset?: number | null; position?: number | null; } | null

Returns

Promise<{ buffer: TBuffer; bytesWritten: number; }>

Call Signature

write(data: string, position?: number | null, encoding?: BufferEncoding | null): Promise<{ buffer: string; bytesWritten: number; }>

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.

Parameters

Parameter	Type	Description
data	string	-
position?	number | null	The 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.
encoding?	BufferEncoding | null	-

Returns

Promise<{ buffer: string; bytesWritten: number; }>

writeFile()

writeFile(data: string | ArrayBufferView, options?: BufferEncoding | { encoding?: BufferEncoding | null | undefined; } | null): Promise<void>

Asynchronously writes data to a file, replacing the file if it already exists.

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.

Parameters

Parameter	Type
data	string | ArrayBufferView
options?	BufferEncoding | { encoding?: BufferEncoding | null | undefined; } | null

Returns

Promise<void>

Interfaces

FileReadOptions

Type Parameters

Type Parameter	Default type
T extends ArrayBufferView	Buffer

Properties

buffer?

optional buffer: T

Default

Buffer.alloc(16384)

length?

optional length: number | null

Default

buffer.byteLength - offset

offset?

optional offset: number | null

Default

0

position?

optional position: number | null

---

FileReadResult

Type Parameters

Type Parameter
T extends ArrayBufferView

Properties

buffer

buffer: T

bytesRead

bytesRead: number

Type Aliases

FileSystemFlags

FileSystemFlags = "a" | "ax" | "a+" | "r" | "r+" | "w" | "wx" | "w+" | "wx+"

Variables

constants

const constants: typeof constants

Functions

access()

access(path: string, mode?: number): Promise<void>

Tests a user's permissions for the file or directory specified by path. The mode argument is an optional integer that specifies the accessibility checks to be performed. mode should be either the value fs.constants.F_OK or a mask consisting of the bitwise OR of any of fs.constants.R_OK, fs.constants.W_OK, and fs.constants.X_OK (e.g.fs.constants.W_OK | fs.constants.R_OK). Check File access constants for possible values of mode.

If the accessibility check is successful, the promise is fulfilled with no value. If any of the accessibility checks fail, the promise is rejected with an Error object. The following example checks if the file/etc/passwd can be read and written by the current process.

import { access, constants } from 'fs/promises';

try {
  await access('/etc/passwd', constants.R_OK | constants.W_OK);
  console.log('can access');
} catch {
  console.error('cannot access');
}

Using fsPromises.access() to check for the accessibility of a file before calling fsPromises.open() is not recommended. Doing so introduces a race condition, since other processes may change the file's state between the two calls. Instead, user code should open/read/write the file directly and handle the error raised if the file is not accessible.

Parameters

Parameter	Type	Description
path	string	-
mode?	number

Returns

Promise<void>

Fulfills with undefined upon success.

---

chmod()

chmod(path: string, mode: number): Promise<void>

Changes the permissions of a file.

Parameters

Parameter	Type
path	string
mode	number

Returns

Promise<void>

Fulfills with undefined upon success.

---

mkdir()

mkdir(path: string, options?: MakeDirectoryOptions): Promise<string>

Asynchronously creates a directory.

The optional options argument can be an object with a mode property and a recursive property indicating whether parent directories should be created. Calling fsPromises.mkdir() when path is a directory that exists results in a rejection only when recursive is false.

import { mkdir } from 'fs/promises';

try {
  const projectFolder = './test/project/123';
  const createDir = await mkdir(projectFolder, { recursive: true });

  console.log(`created ${createDir}`);
} catch (err) {
  console.error(err.message);
}

Parameters

Parameter	Type
path	string
options?	MakeDirectoryOptions

Returns

Promise<string>

Upon success, fulfills with undefined if recursive is false, or the first directory path created if recursive is true.

---

mkdtemp()

mkdtemp(prefix: string): Promise<string>

Creates a unique temporary directory. A unique directory name is generated by appending six random characters to the end of the provided prefix. Due to platform inconsistencies, avoid trailing X characters in prefix. Some platforms, notably the BSDs, can return more than six random characters, and replace trailing X characters in prefix with random characters.

import { mkdtemp } from 'fs/promises';
import { join } from 'path';
import { tmpdir } from 'os';

try {
  await mkdtemp(join(tmpdir(), 'foo-'));
} catch (err) {
  console.error(err);
}

The fsPromises.mkdtemp() method will append the six randomly selected characters directly to the prefix string. For instance, given a directory /tmp, if the intention is to create a temporary directory within /tmp, the prefix must end with a trailing platform-specific path separator (require('path').sep).

Parameters

Parameter	Type
prefix	string

Returns

Promise<string>

Fulfills with a string containing the file system path of the newly created temporary directory.

---

open()

open(path: string, flags?: FileSystemFlags, mode?: number): Promise<FileHandle>

Opens a FileHandle.

Refer to the POSIX open(2) documentation for more detail.

Some characters (< > : " / \ | ? *) are reserved under Windows as documented by Naming Files, Paths, and Namespaces.

Parameters

Parameter	Type	Description
path	string	-
flags?	FileSystemFlags	See {FileSystemFlags}.
mode?	number	Sets the file mode if the file is created (UNIX).

Returns

Promise<FileHandle>

Fulfills with a {FileHandle} object.

---

readdir()

Call Signature

readdir(path: string, options?: object): Promise<string[]>

Reads the contents of a directory.

If options.withFileTypes is set to true, the returned array will contain fs.Dirent objects.

import { readdir } from 'fs/promises';

try {
  const files = await readdir(path);
  for (const file of files)
    console.log(file);
} catch (err) {
  console.error(err);
}

Parameters

Parameter	Type
path	string
options?	{ recursive?: boolean; withFileTypes?: false; }
options.recursive?	boolean
options.withFileTypes?	false

Returns

Promise<string[]>

Fulfills with an array of the names of the files in the directory excluding '.' and '..'.

Call Signature

readdir(path: string, options: object): Promise<Dirent[]>

Asynchronous readdir(2) - read a directory.

Parameters

Parameter	Type	Description
path	string	A path to a file. If a URL is provided, it must use the file: protocol.
options	{ recursive?: boolean; withFileTypes: true; }	If called with withFileTypes: true the result data will be an array of Dirent.
options.recursive?	boolean	-
options.withFileTypes	true	-

Returns

Promise<Dirent[]>

---

readFile()

Call Signature

readFile(path: string, options?: { encoding?: null; } | null): Promise<Buffer>

Asynchronously reads the entire contents of a file.

If no encoding is specified (using options.encoding), the data is returned as a Buffer object. Otherwise, the data will be a string.

If options is a string, then it specifies the encoding.

When the path is a directory, the behavior of fsPromises.readFile() is platform-specific. On macOS, Linux, and Windows, the promise will be rejected with an error. On FreeBSD, a representation of the directory's contents will be returned.

An example of reading a package.json file.

import { readFile } from 'fs/promises';
try {
  const filePath = './package.json';
  const contents = await readFile(filePath, { encoding: 'utf8' });
  console.log(contents);
} catch (err) {
  console.error(err.message);
}

Parameters

Parameter	Type	Description
path	string	filename or FileHandle
options?	{ encoding?: null; } | null	-

Returns

Promise<Buffer>

Fulfills with the contents of the file.

Call Signature

readFile(path: string, options: BufferEncoding | { encoding: BufferEncoding; }): Promise<string>

Asynchronously reads the entire contents of a file.

Parameters

Parameter	Type	Description
path	string	A path to a file. If a URL is provided, it must use the file: protocol. If a FileHandle is provided, the underlying file will not be closed automatically.
options	BufferEncoding | { encoding: BufferEncoding; }	An object that may contain an optional flag. If a flag is not provided, it defaults to 'r'.

Returns

Promise<string>

---

rename()

rename(oldPath: string, newPath: string): Promise<void>

Asynchronously renames a file or directory from oldPath to newPath.

import { rename } from 'fs/promises';

try {
  await rename('oldfile.txt', 'newfile.txt');
  console.log('Rename complete!');
} catch (err) {
  console.error(err);
}

Parameters

Parameter	Type	Description
oldPath	string	A path to a file or directory.
newPath	string	The new path for the file or directory.

Returns

Promise<void>

Fulfills with undefined upon success.

---

rm()

rm(path: string, options?: RmOptions): Promise<void>

Removes files and directories (modeled on the standard POSIX rm utility).

Parameters

Parameter	Type
path	string
options?	RmOptions

Returns

Promise<void>

Fulfills with undefined upon success.

---

rmdir()

rmdir(path: string, options?: RmDirOptions): Promise<void>

Removes the directory identified by path.

Using fsPromises.rmdir() on a file (not a directory) results in the promise being rejected with an ENOENT error on Windows and an ENOTDIR error on POSIX.

To get a behavior similar to the rm -rf Unix command, use fsPromises.rm() with options { recursive: true, force: true }.

Parameters

Parameter	Type
path	string
options?	RmDirOptions

Returns

Promise<void>

Fulfills with undefined upon success.

---

stat()

stat(path: string): Promise<Stats>

Asynchronous stat - Get file status.

Parameters

Parameter	Type	Description
path	string	A path to a file.

Returns

Promise<Stats>

Fulfills with the {fs.Stats} object for the given path.

---

symlink()

symlink(target: string, path: string, type?: "dir" | "file" | "junction" | null): Promise<void>

Creates a symbolic link.

The type argument is only used on Windows platforms and can be one of 'dir', 'file', or 'junction'. If the type argument is not a string, LLRT will autodetect target type and use 'file' or 'dir'. If the target does not exist, 'file' will be used. Windows junction points require the destination path to be absolute. When using 'junction', the target argument will automatically be normalized to absolute path. Junction points on NTFS volumes can only point to directories.

Parameters

Parameter	Type	Description
target	string	-
path	string	-
type?	"dir" | "file" | "junction" | null

Returns

Promise<void>

Fulfills with undefined upon success.

---

writeFile()

writeFile(file: string, data: string | ArrayBuffer | SharedArrayBuffer | ArrayBufferView | Buffer, options?: object): Promise<void>

Asynchronously writes data to a file, replacing the file if it already exists.

The encoding option is ignored if data is a buffer.

It is unsafe to use fsPromises.writeFile() multiple times on the same file without waiting for the promise to be settled.

Similarly to fsPromises.readFile - fsPromises.writeFile is a convenience method that performs multiple write calls internally to write the buffer passed to it.

Parameters

Parameter	Type	Description
file	string	filename or FileHandle
data	string | ArrayBuffer | SharedArrayBuffer | ArrayBufferView | Buffer	-
options?	{ mode?: number; }	-
options.mode?	number	-

Returns

Promise<void>

Fulfills with undefined upon success.