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Node.js module

fs/promises

The 'node:fs/promises' module provides Promise-based variants of the fs API, allowing asynchronous file operations to be performed with async/await syntax.

  • const constants: typeof fsConstants
  • function access(
    path: PathLike,
    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 'node: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.

    @returns

    Fulfills with undefined upon success.

  • function appendFile(
    path: PathLike | FileHandle,
    data: string | Uint8Array<ArrayBufferLike>,
    options?: null | BufferEncoding | ObjectEncodingOptions & FlagAndOpenMode & { flush: boolean }
    ): Promise<void>;

    Asynchronously append data to a file, creating the file if it does not yet exist. data can be a string or a Buffer.

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

    The mode option only affects the newly created file. See fs.open() for more details.

    The path may be specified as a FileHandle that has been opened for appending (using fsPromises.open()).

    @param path

    filename or {FileHandle}

    @returns

    Fulfills with undefined upon success.

  • function chmod(
    path: PathLike,
    mode: Mode
    ): Promise<void>;

    Changes the permissions of a file.

    @returns

    Fulfills with undefined upon success.

  • function chown(
    path: PathLike,
    uid: number,
    gid: number
    ): Promise<void>;

    Changes the ownership of a file.

    @returns

    Fulfills with undefined upon success.

  • function copyFile(
    src: PathLike,
    dest: PathLike,
    mode?: number
    ): Promise<void>;

    Asynchronously copies src to dest. By default, dest is overwritten if it already exists.

    No guarantees are made about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, an attempt will be made to remove the destination.

    import { copyFile, constants } from 'node:fs/promises';

try {
  await copyFile('source.txt', 'destination.txt');
  console.log('source.txt was copied to destination.txt');
} catch {
  console.error('The file could not be copied');
}

// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.
try {
  await copyFile('source.txt', 'destination.txt', constants.COPYFILE_EXCL);
  console.log('source.txt was copied to destination.txt');
} catch {
  console.error('The file could not be copied');
}
    @param src

    source filename to copy

    @param dest

    destination filename of the copy operation

    @param mode

    Optional modifiers that specify the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE)

    @returns

    Fulfills with undefined upon success.

  • function cp(
    source: string | URL,
    destination: string | URL,
    opts?: CopyOptions
    ): Promise<void>;

    Asynchronously copies the entire directory structure from src to dest, including subdirectories and files.

    When copying a directory to another directory, globs are not supported and behavior is similar to cp dir1/ dir2/.

    @returns

    Fulfills with undefined upon success.

  • function exists(
    path: PathLike
    ): Promise<boolean>;
  • function glob(
    pattern: string | string[]
    ): AsyncIterator<string>;

    Retrieves the files matching the specified pattern.

    function glob(
    pattern: string | string[],
    opt: GlobOptionsWithFileTypes
    ): AsyncIterator<Dirent<string>>;

    Retrieves the files matching the specified pattern.

    function glob(
    pattern: string | string[],
    opt: GlobOptionsWithoutFileTypes
    ): AsyncIterator<string>;

    Retrieves the files matching the specified pattern.

    function glob(
    pattern: string | string[],
    opt: GlobOptions
    ): AsyncIterator<string | Dirent<string>>;

    Retrieves the files matching the specified pattern.

  • function lchown(
    path: PathLike,
    uid: number,
    gid: number
    ): Promise<void>;

    Changes the ownership on a symbolic link.

    @returns

    Fulfills with undefined upon success.

  • function lstat(
    path: PathLike,
    opts?: StatOptions & { bigint: false }
    ): Promise<Stats>;

    Equivalent to fsPromises.stat() unless path refers to a symbolic link, in which case the link itself is stat-ed, not the file that it refers to. Refer to the POSIX lstat(2) document for more detail.

    @returns

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

    function lstat(
    path: PathLike,
    opts: StatOptions & { bigint: true }
    ): Promise<BigIntStats>;

    Equivalent to fsPromises.stat() unless path refers to a symbolic link, in which case the link itself is stat-ed, not the file that it refers to. Refer to the POSIX lstat(2) document for more detail.

    @returns

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

    function lstat(
    path: PathLike,
    opts?: StatOptions
    ): Promise<Stats | BigIntStats>;

    Equivalent to fsPromises.stat() unless path refers to a symbolic link, in which case the link itself is stat-ed, not the file that it refers to. Refer to the POSIX lstat(2) document for more detail.

    @returns

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

  • function lutimes(
    path: PathLike,
    atime: TimeLike,
    mtime: TimeLike
    ): Promise<void>;

    Changes the access and modification times of a file in the same way as fsPromises.utimes(), with the difference that if the path refers to a symbolic link, then the link is not dereferenced: instead, the timestamps of the symbolic link itself are changed.

    @returns

    Fulfills with undefined upon success.

  • function mkdir(
    path: PathLike,
    options: MakeDirectoryOptions & { recursive: true }
    ): Promise<undefined | string>;

    Asynchronously creates a directory.

    The optional options argument can be an integer specifying mode (permission and sticky bits), or 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 'node:fs/promises';

try {
  const projectFolder = new URL('./test/project/', import.meta.url);
  const createDir = await mkdir(projectFolder, { recursive: true });

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

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

    function mkdir(
    path: PathLike,
    options?: null | Mode | MakeDirectoryOptions & { recursive: false }
    ): Promise<void>;

    Asynchronous mkdir(2) - create a directory.

    @param path

    A path to a file. If a URL is provided, it must use the file: protocol.

    @param options

    Either the file mode, or an object optionally specifying the file mode and whether parent folders should be created. If a string is passed, it is parsed as an octal integer. If not specified, defaults to 0o777.

    function mkdir(
    path: PathLike,
    options?: null | Mode | MakeDirectoryOptions
    ): Promise<undefined | string>;

    Asynchronous mkdir(2) - create a directory.

    @param path

    A path to a file. If a URL is provided, it must use the file: protocol.

    @param options

    Either the file mode, or an object optionally specifying the file mode and whether parent folders should be created. If a string is passed, it is parsed as an octal integer. If not specified, defaults to 0o777.

  • function mkdtemp(
    prefix: string,
    options?: null | BufferEncoding | ObjectEncodingOptions
    ): 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.

    The optional options argument can be a string specifying an encoding, or an object with an encoding property specifying the character encoding to use.

    import { mkdtemp } from 'node:fs/promises';
import { join } from 'node:path';
import { tmpdir } from 'node: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 (import { sep } from 'node:path').

    @returns

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

    function mkdtemp(
    prefix: string,
    options: BufferEncodingOption
    ): Promise<Buffer<ArrayBufferLike>>;

    Asynchronously creates a unique temporary directory. Generates six random characters to be appended behind a required prefix to create a unique temporary directory.

    @param options

    The encoding (or an object specifying the encoding), used as the encoding of the result. If not provided, 'utf8' is used.

    function mkdtemp(
    prefix: string,
    options?: null | BufferEncoding | ObjectEncodingOptions
    ): Promise<string | Buffer<ArrayBufferLike>>;

    Asynchronously creates a unique temporary directory. Generates six random characters to be appended behind a required prefix to create a unique temporary directory.

    @param options

    The encoding (or an object specifying the encoding), used as the encoding of the result. If not provided, 'utf8' is used.

  • function open(
    path: PathLike,
    flags?: string | number,
    mode?: Mode
    ): 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. Under NTFS, if the filename contains a colon, Node.js will open a file system stream, as described by this MSDN page.

    @param flags

    See support of file system flags``.

    @param mode

    Sets the file mode (permission and sticky bits) if the file is created.

    @returns

    Fulfills with a {FileHandle} object.

  • function opendir(
    path: PathLike,
    options?: OpenDirOptions
    ): Promise<Dir>;

    Asynchronously open a directory for iterative scanning. See the POSIX opendir(3) documentation for more detail.

    Creates an fs.Dir, which contains all further functions for reading from and cleaning up the directory.

    The encoding option sets the encoding for the path while opening the directory and subsequent read operations.

    Example using async iteration:

    import { opendir } from 'node:fs/promises';

try {
  const dir = await opendir('./');
  for await (const dirent of dir)
    console.log(dirent.name);
} catch (err) {
  console.error(err);
}

    When using the async iterator, the fs.Dir object will be automatically closed after the iterator exits.

    @returns

    Fulfills with an {fs.Dir}.

  • function readdir(
    path: PathLike,
    options?: null | BufferEncoding | ObjectEncodingOptions & { recursive: boolean; withFileTypes: false }
    ): Promise<string[]>;

    Reads the contents of a directory.

    The optional options argument can be a string specifying an encoding, or an object with an encoding property specifying the character encoding to use for the filenames. If the encoding is set to 'buffer', the filenames returned will be passed as Buffer objects.

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

    import { readdir } from 'node:fs/promises';

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

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

    function readdir(
    path: PathLike,
    options: 'buffer' | { encoding: 'buffer'; recursive: boolean; withFileTypes: false }
    ): Promise<Buffer<ArrayBufferLike>[]>;

    Asynchronous readdir(3) - read a directory.

    @param path

    A path to a file. If a URL is provided, it must use the file: protocol.

    @param options

    The encoding (or an object specifying the encoding), used as the encoding of the result. If not provided, 'utf8' is used.

    function readdir(
    path: PathLike,
    options?: null | BufferEncoding | ObjectEncodingOptions & { recursive: boolean; withFileTypes: false }
    ): Promise<string[] | Buffer<ArrayBufferLike>[]>;

    Asynchronous readdir(3) - read a directory.

    @param path

    A path to a file. If a URL is provided, it must use the file: protocol.

    @param options

    The encoding (or an object specifying the encoding), used as the encoding of the result. If not provided, 'utf8' is used.

    function readdir(
    path: PathLike,
    options: ObjectEncodingOptions & { recursive: boolean; withFileTypes: true }
    ): Promise<Dirent<string>[]>;

    Asynchronous readdir(3) - read a directory.

    @param path

    A path to a file. If a URL is provided, it must use the file: protocol.

    @param options

    If called with withFileTypes: true the result data will be an array of Dirent.

    function readdir(
    path: PathLike,
    options: { encoding: 'buffer'; recursive: boolean; withFileTypes: true }
    ): Promise<Dirent<Buffer<ArrayBufferLike>>[]>;

    Asynchronous readdir(3) - read a directory.

    @param path

    A path to a directory. If a URL is provided, it must use the file: protocol.

    @param options

    Must include withFileTypes: true and encoding: 'buffer'.

  • function readFile(
    path: PathLike | FileHandle,
    options?: null | { encoding: null; flag: OpenMode } & Abortable
    ): Promise<Buffer<ArrayBufferLike>>;

    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 located in the same directory of the running code:

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

    It is possible to abort an ongoing readFile using an AbortSignal. If a request is aborted the promise returned is rejected with an AbortError:

    import { readFile } from 'node:fs/promises';

try {
  const controller = new AbortController();
  const { signal } = controller;
  const promise = readFile(fileName, { signal });

  // Abort the request before the promise settles.
  controller.abort();

  await promise;
} catch (err) {
  // When a request is aborted - err is an AbortError
  console.error(err);
}

    Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering fs.readFile performs.

    Any specified FileHandle has to support reading.

    @param path

    filename or FileHandle

    @returns

    Fulfills with the contents of the file.

    function readFile(
    path: PathLike | FileHandle,
    options: BufferEncoding | { encoding: BufferEncoding; flag: unknown } & Abortable
    ): Promise<string>;

    Asynchronously reads the entire contents of a file.

    @param path

    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.

    @param options

    An object that may contain an optional flag. If a flag is not provided, it defaults to 'r'.

    function readFile(
    path: PathLike | FileHandle,
    options?: null | BufferEncoding | ObjectEncodingOptions & Abortable & { flag: unknown }
    ): Promise<string | Buffer<ArrayBufferLike>>;

    Asynchronously reads the entire contents of a file.

    @param path

    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.

    @param options

    An object that may contain an optional flag. If a flag is not provided, it defaults to 'r'.

  • function readlink(
    path: PathLike,
    options?: null | BufferEncoding | ObjectEncodingOptions
    ): Promise<string>;

    Reads the contents of the symbolic link referred to by path. See the POSIX readlink(2) documentation for more detail. The promise is fulfilled with thelinkString upon success.

    The optional options argument can be a string specifying an encoding, or an object with an encoding property specifying the character encoding to use for the link path returned. If the encoding is set to 'buffer', the link path returned will be passed as a Buffer object.

    @returns

    Fulfills with the linkString upon success.

    function readlink(
    path: PathLike,
    options: BufferEncodingOption
    ): Promise<Buffer<ArrayBufferLike>>;

    Asynchronous readlink(2) - read value of a symbolic link.

    @param path

    A path to a file. If a URL is provided, it must use the file: protocol.

    @param options

    The encoding (or an object specifying the encoding), used as the encoding of the result. If not provided, 'utf8' is used.

    function readlink(
    path: PathLike,
    options?: null | string | ObjectEncodingOptions
    ): Promise<string | Buffer<ArrayBufferLike>>;

    Asynchronous readlink(2) - read value of a symbolic link.

    @param path

    A path to a file. If a URL is provided, it must use the file: protocol.

    @param options

    The encoding (or an object specifying the encoding), used as the encoding of the result. If not provided, 'utf8' is used.

  • function realpath(
    path: PathLike,
    options?: null | BufferEncoding | ObjectEncodingOptions
    ): Promise<string>;

    Determines the actual location of path using the same semantics as the fs.realpath.native() function.

    Only paths that can be converted to UTF8 strings are supported.

    The optional options argument can be a string specifying an encoding, or an object with an encoding property specifying the character encoding to use for the path. If the encoding is set to 'buffer', the path returned will be passed as a Buffer object.

    On Linux, when Node.js is linked against musl libc, the procfs file system must be mounted on /proc in order for this function to work. Glibc does not have this restriction.

    @returns

    Fulfills with the resolved path upon success.

    function realpath(
    path: PathLike,
    options: BufferEncodingOption
    ): Promise<Buffer<ArrayBufferLike>>;

    Asynchronous realpath(3) - return the canonicalized absolute pathname.

    @param path

    A path to a file. If a URL is provided, it must use the file: protocol.

    @param options

    The encoding (or an object specifying the encoding), used as the encoding of the result. If not provided, 'utf8' is used.

    function realpath(
    path: PathLike,
    options?: null | BufferEncoding | ObjectEncodingOptions
    ): Promise<string | Buffer<ArrayBufferLike>>;

    Asynchronous realpath(3) - return the canonicalized absolute pathname.

    @param path

    A path to a file. If a URL is provided, it must use the file: protocol.

    @param options

    The encoding (or an object specifying the encoding), used as the encoding of the result. If not provided, 'utf8' is used.

  • function rename(
    oldPath: PathLike,
    newPath: PathLike
    ): Promise<void>;

    Renames oldPath to newPath.

    @returns

    Fulfills with undefined upon success.

  • function rm(
    path: PathLike,
    options?: RmOptions
    ): Promise<void>;

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

    @returns

    Fulfills with undefined upon success.

  • function rmdir(
    path: PathLike,
    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 }.

    @returns

    Fulfills with undefined upon success.

  • function stat(
    path: PathLike,
    opts?: StatOptions & { bigint: false }
    ): Promise<Stats>;
    @returns

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

    function stat(
    path: PathLike,
    opts: StatOptions & { bigint: true }
    ): Promise<BigIntStats>;
    @returns

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

    function stat(
    path: PathLike,
    opts?: StatOptions
    ): Promise<Stats | BigIntStats>;
    @returns

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

  • function statfs(
    path: PathLike,
    opts?: StatFsOptions & { bigint: false }
    ): Promise<StatsFs>;
    @returns

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

    function statfs(
    path: PathLike,
    opts: StatFsOptions & { bigint: true }
    ): Promise<BigIntStatsFs>;
    @returns

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

    function statfs(
    path: PathLike,
    opts?: StatFsOptions
    ): Promise<StatsFs | BigIntStatsFs>;
    @returns

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

  • function truncate(
    path: PathLike,
    len?: number
    ): Promise<void>;

    Truncates (shortens or extends the length) of the content at path to len bytes.

    @returns

    Fulfills with undefined upon success.

  • function utimes(
    path: PathLike,
    atime: TimeLike,
    mtime: TimeLike
    ): Promise<void>;

    Change the file system timestamps of the object referenced by path.

    The atime and mtime arguments follow these rules:

    • Values can be either numbers representing Unix epoch time, Dates, or a numeric string like '123456789.0'.
    • If the value can not be converted to a number, or is NaN, Infinity, or -Infinity, an Error will be thrown.
    @returns

    Fulfills with undefined upon success.

  • function watch(
    filename: PathLike,
    options: 'buffer' | WatchOptions & { encoding: 'buffer' }
    ): AsyncIterable<FileChangeInfo<Buffer<ArrayBufferLike>>>;

    Returns an async iterator that watches for changes on filename, where filenameis either a file or a directory.

    import { watch } from 'node:fs/promises';

const ac = new AbortController();
const { signal } = ac;
setTimeout(() => ac.abort(), 10000);

(async () => {
  try {
    const watcher = watch(__filename, { signal });
    for await (const event of watcher)
      console.log(event);
  } catch (err) {
    if (err.name === 'AbortError')
      return;
    throw err;
  }
})();

    On most platforms, 'rename' is emitted whenever a filename appears or disappears in the directory.

    All the caveats for fs.watch() also apply to fsPromises.watch().

    @returns

    of objects with the properties:

    function watch(
    filename: PathLike,
    options?: BufferEncoding | WatchOptions
    ): AsyncIterable<FileChangeInfo<string>>;

    Watch for changes on filename, where filename is either a file or a directory, returning an FSWatcher.

    @param filename

    A path to a file or directory. If a URL is provided, it must use the file: protocol.

    @param options

    Either the encoding for the filename provided to the listener, or an object optionally specifying encoding, persistent, and recursive options. If encoding is not supplied, the default of 'utf8' is used. If persistent is not supplied, the default of true is used. If recursive is not supplied, the default of false is used.

    function watch(
    filename: PathLike,
    options: string | WatchOptions
    ): AsyncIterable<FileChangeInfo<Buffer<ArrayBufferLike>>, any, any> | AsyncIterable<FileChangeInfo<string>, any, any>;

    Watch for changes on filename, where filename is either a file or a directory, returning an FSWatcher.

    @param filename

    A path to a file or directory. If a URL is provided, it must use the file: protocol.

    @param options

    Either the encoding for the filename provided to the listener, or an object optionally specifying encoding, persistent, and recursive options. If encoding is not supplied, the default of 'utf8' is used. If persistent is not supplied, the default of true is used. If recursive is not supplied, the default of false is used.

  • function writeFile(
    file: PathLike | FileHandle,
    data: string | Stream | ArrayBufferView<ArrayBufferLike> | Iterable<unknown, any, any> | AsyncIterable<unknown, any, any>,
    options?: null | BufferEncoding | ObjectEncodingOptions & { flag: unknown; flush: boolean; mode: unknown } & Abortable
    ): Promise<void>;

    Asynchronously 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 encoding option is ignored if data is a buffer.

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

    The mode option only affects the newly created file. See fs.open() for more details.

    Any specified FileHandle has to support writing.

    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. For performance sensitive code consider using fs.createWriteStream() or filehandle.createWriteStream().

    It is possible to use an AbortSignal to cancel an fsPromises.writeFile(). Cancelation is "best effort", and some amount of data is likely still to be written.

    import { writeFile } from 'node:fs/promises';
import { Buffer } from 'node:buffer';

try {
  const controller = new AbortController();
  const { signal } = controller;
  const data = new Uint8Array(Buffer.from('Hello Node.js'));
  const promise = writeFile('message.txt', data, { signal });

  // Abort the request before the promise settles.
  controller.abort();

  await promise;
} catch (err) {
  // When a request is aborted - err is an AbortError
  console.error(err);
}

    Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering fs.writeFile performs.

    @param file

    filename or FileHandle

    @returns

    Fulfills with undefined upon success.

Type definitions

  • interface CreateReadStreamOptions

  • interface CreateWriteStreamOptions

  • interface FileChangeInfo<T extends string | Buffer>

  • interface FileHandle

    • readonly fd: number

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

    • [Symbol.asyncDispose](): Promise<void>;

      An alias for ().

    • data: string | Uint8Array<ArrayBufferLike>,
      options?: null | BufferEncoding | ObjectEncodingOptions & Abortable
      ): Promise<void>;

      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().

      @returns

      Fulfills with undefined upon success.

    • mode: Mode
      ): Promise<void>;

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

      @param mode

      the file mode bit mask.

      @returns

      Fulfills with undefined upon success.

    • uid: number,
      gid: number
      ): Promise<void>;

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

      @param uid

      The file's new owner's user id.

      @param gid

      The file's new group's group id.

      @returns

      Fulfills with undefined upon success.

    • close(): Promise<void>;

      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();
}
      @returns

      Fulfills with undefined upon success.

    • options?: CreateReadStreamOptions

      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 });
    • options?: CreateWriteStreamOptions

      options 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.

    • 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

      Fulfills with undefined upon success.

    • read<T extends ArrayBufferView<ArrayBufferLike>>(
      buffer: T,
      offset?: null | number,
      length?: null | number,
      position?: null | number
      ): 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.

      @param buffer

      A buffer that will be filled with the file data read.

      @param offset

      The location in the buffer at which to start filling.

      @param length

      The number of bytes to read.

      @param position

      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

      Fulfills upon success with an object with two properties:

      read<T extends ArrayBufferView<ArrayBufferLike> = Buffer<ArrayBufferLike>>(
      buffer: T,
      options?: FileReadOptions<T>
      ): Promise<FileReadResult<T>>;
      read<T extends ArrayBufferView<ArrayBufferLike> = Buffer<ArrayBufferLike>>(
      options?: FileReadOptions<T>
      ): Promise<FileReadResult<T>>;

    • Returns 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.

    • options?: null | { encoding: null } & Abortable
      ): Promise<Buffer<ArrayBufferLike>>;

      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.

      @returns

      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.

      options: BufferEncoding | { encoding: BufferEncoding } & Abortable
      ): Promise<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.

      options?: null | BufferEncoding | ObjectEncodingOptions & Abortable
      ): Promise<string | Buffer<ArrayBufferLike>>;

      Asynchronously reads the entire contents of a file. The underlying file will not be closed automatically. The FileHandle must have been opened for reading.

    • options?: CreateReadStreamOptions

      Convenience 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);
}
    • buffers: readonly ArrayBufferView<ArrayBufferLike>[],
      position?: number
      ): Promise<ReadVResult>;
      @param position

      The 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.

      @returns

      Fulfills upon success an object containing two properties:

    • opts?: StatOptions & { bigint: false }
      ): Promise<Stats>;
      @returns

      Fulfills with an {fs.Stats} for the file.

      opts: StatOptions & { bigint: true }
      ): Promise<BigIntStats>;
      opts?: StatOptions
      ): Promise<Stats | BigIntStats>;
    • 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

      Fulfills with undefined upon success.

    • 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 '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.

      @returns

      Fulfills with undefined upon success.

    • atime: TimeLike,
      mtime: TimeLike
      ): Promise<void>;

      Change the file system timestamps of the object referenced by the FileHandle then fulfills the promise with no arguments upon success.

    • write<TBuffer extends Uint8Array<ArrayBufferLike>>(
      buffer: TBuffer,
      offset?: null | number,
      length?: null | number,
      position?: null | number
      ): 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.

      @param offset

      The start position from within buffer where the data to write begins.

      @param length

      The number of bytes from buffer to write.

      @param position

      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.

      write<TBuffer extends Uint8Array<ArrayBufferLike>>(
      buffer: TBuffer,
      options?: { length: number; offset: number; position: number }
      ): Promise<{ buffer: TBuffer; bytesWritten: number }>;
      data: string,
      position?: null | number,
      encoding?: null | BufferEncoding
      ): Promise<{ buffer: string; bytesWritten: number }>;
    • data: string | Uint8Array<ArrayBufferLike>,
      options?: null | BufferEncoding | ObjectEncodingOptions & Abortable
      ): Promise<void>;

      Asynchronously 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.

    • buffers: readonly ArrayBufferView<ArrayBufferLike>[],
      position?: number
      ): Promise<WriteVResult>;

      Write 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.

      @param position

      The 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.

  • interface FileReadOptions<T extends NodeJS.ArrayBufferView = Buffer>

  • interface FileReadResult<T extends NodeJS.ArrayBufferView>