Interface FileSystemPromises

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_OKor 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 resolved 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');
}
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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.

Since

v10.0.0

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()).

Since

v10.0.0

Changes the permissions of a file.

Since

v10.0.0

Changes the ownership of a file.

Since

v10.0.0

Creates a new link from the existingPath to the newPath. See the POSIX link(2) documentation for more detail.

Since

v10.0.0

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.

Since

v10.0.0

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 recursiveproperty indicating whether parent directories should be created. CallingfsPromises.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);
}
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Since

v10.0.0

Asynchronous mkdir(2) - create a directory.

Asynchronous mkdir(2) - create a directory.

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);
}
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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, theprefix must end with a trailing platform-specific path separator (require('node:path').sep).

Since

v10.0.0

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

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

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.

Since

v10.0.0

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);
}
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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);
}
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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.

Since

v10.0.0

Asynchronously reads the entire contents of a file.

Asynchronously reads the entire contents of a file.

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 resolved 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);
}
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Since

v10.0.0

Asynchronous readdir(3) - read a directory.

Asynchronous readdir(3) - read a directory.

Asynchronous readdir(3) - read a directory.

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

Since

v10.0.0

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

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

Renames oldPath to newPath.

Since

v10.0.0

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 ENOTDIRerror on POSIX.

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

Since

v10.0.0

Since

v10.0.0

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, Node.js 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.

Since

v10.0.0

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

Since

v10.0.0

If path refers to a symbolic link, then the link is removed without affecting the file or directory to which that link refers. If the path refers to a file path that is not a symbolic link, the file is deleted. See the POSIX unlink(2) documentation for more detail.

Since

v10.0.0

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.

Since

v10.0.0

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

Since

v10.0.0