File system | Node.js v25.9.0 Documentation
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Table of contents
File system
Promise example
Callback example
Synchronous example
Promises API
Class:
FileHandle
Event:
'close'
filehandle.appendFile(data[, options])
filehandle.chmod(mode)
filehandle.chown(uid, gid)
filehandle.close()
filehandle.createReadStream([options])
filehandle.createWriteStream([options])
filehandle.datasync()
filehandle.fd
filehandle.pull([...transforms][, options])
filehandle.pullSync([...transforms][, options])
filehandle.read(buffer, offset, length, position)
filehandle.read([options])
filehandle.read(buffer[, options])
filehandle.readableWebStream([options])
filehandle.readFile(options)
filehandle.readLines([options])
filehandle.readv(buffers[, position])
filehandle.stat([options])
filehandle.sync()
filehandle.truncate(len)
filehandle.utimes(atime, mtime)
filehandle.write(buffer, offset[, length[, position]])
filehandle.write(buffer[, options])
filehandle.write(string[, position[, encoding]])
filehandle.writeFile(data, options)
filehandle.writev(buffers[, position])
filehandle.writer([options])
filehandle[Symbol.asyncDispose]()
fsPromises.access(path[, mode])
fsPromises.appendFile(path, data[, options])
fsPromises.chmod(path, mode)
fsPromises.chown(path, uid, gid)
fsPromises.copyFile(src, dest[, mode])
fsPromises.cp(src, dest[, options])
fsPromises.glob(pattern[, options])
fsPromises.lchmod(path, mode)
fsPromises.lchown(path, uid, gid)
fsPromises.lutimes(path, atime, mtime)
fsPromises.link(existingPath, newPath)
fsPromises.lstat(path[, options])
fsPromises.mkdir(path[, options])
fsPromises.mkdtemp(prefix[, options])
fsPromises.mkdtempDisposable(prefix[, options])
fsPromises.open(path, flags[, mode])
fsPromises.opendir(path[, options])
fsPromises.readdir(path[, options])
fsPromises.readFile(path[, options])
fsPromises.readlink(path[, options])
fsPromises.realpath(path[, options])
fsPromises.rename(oldPath, newPath)
fsPromises.rmdir(path[, options])
fsPromises.rm(path[, options])
fsPromises.stat(path[, options])
fsPromises.statfs(path[, options])
fsPromises.symlink(target, path[, type])
fsPromises.truncate(path[, len])
fsPromises.unlink(path)
fsPromises.utimes(path, atime, mtime)
fsPromises.watch(filename[, options])
fsPromises.writeFile(file, data[, options])
fsPromises.constants
Callback API
fs.access(path[, mode], callback)
fs.appendFile(path, data[, options], callback)
fs.chmod(path, mode, callback)
File modes
fs.chown(path, uid, gid, callback)
fs.close(fd[, callback])
fs.copyFile(src, dest[, mode], callback)
fs.cp(src, dest[, options], callback)
fs.createReadStream(path[, options])
fs.createWriteStream(path[, options])
fs.exists(path, callback)
fs.fchmod(fd, mode, callback)
fs.fchown(fd, uid, gid, callback)
fs.fdatasync(fd, callback)
fs.fstat(fd[, options], callback)
fs.fsync(fd, callback)
fs.ftruncate(fd[, len], callback)
fs.futimes(fd, atime, mtime, callback)
fs.glob(pattern[, options], callback)
fs.lchmod(path, mode, callback)
fs.lchown(path, uid, gid, callback)
fs.lutimes(path, atime, mtime, callback)
fs.link(existingPath, newPath, callback)
fs.lstat(path[, options], callback)
fs.mkdir(path[, options], callback)
fs.mkdtemp(prefix[, options], callback)
fs.open(path[, flags[, mode]], callback)
fs.openAsBlob(path[, options])
fs.opendir(path[, options], callback)
fs.read(fd, buffer, offset, length, position, callback)
fs.read(fd[, options], callback)
fs.read(fd, buffer[, options], callback)
fs.readdir(path[, options], callback)
fs.readFile(path[, options], callback)
File descriptors
Performance Considerations
fs.readlink(path[, options], callback)
fs.readv(fd, buffers[, position], callback)
fs.realpath(path[, options], callback)
fs.realpath.native(path[, options], callback)
fs.rename(oldPath, newPath, callback)
fs.rmdir(path[, options], callback)
fs.rm(path[, options], callback)
fs.stat(path[, options], callback)
fs.statfs(path[, options], callback)
fs.symlink(target, path[, type], callback)
fs.truncate(path[, len], callback)
fs.unlink(path, callback)
fs.unwatchFile(filename[, listener])
fs.utimes(path, atime, mtime, callback)
fs.watch(filename[, options][, listener])
Caveats
Availability
Inodes
Filename argument
fs.watchFile(filename[, options], listener)
fs.write(fd, buffer, offset[, length[, position]], callback)
fs.write(fd, buffer[, options], callback)
fs.write(fd, string[, position[, encoding]], callback)
fs.writeFile(file, data[, options], callback)
Using
fs.writeFile()
with file descriptors
fs.writev(fd, buffers[, position], callback)
Synchronous API
fs.accessSync(path[, mode])
fs.appendFileSync(path, data[, options])
fs.chmodSync(path, mode)
fs.chownSync(path, uid, gid)
fs.closeSync(fd)
fs.copyFileSync(src, dest[, mode])
fs.cpSync(src, dest[, options])
fs.existsSync(path)
fs.fchmodSync(fd, mode)
fs.fchownSync(fd, uid, gid)
fs.fdatasyncSync(fd)
fs.fstatSync(fd[, options])
fs.fsyncSync(fd)
fs.ftruncateSync(fd[, len])
fs.futimesSync(fd, atime, mtime)
fs.globSync(pattern[, options])
fs.lchmodSync(path, mode)
fs.lchownSync(path, uid, gid)
fs.lutimesSync(path, atime, mtime)
fs.linkSync(existingPath, newPath)
fs.lstatSync(path[, options])
fs.mkdirSync(path[, options])
fs.mkdtempSync(prefix[, options])
fs.mkdtempDisposableSync(prefix[, options])
fs.opendirSync(path[, options])
fs.openSync(path[, flags[, mode]])
fs.readdirSync(path[, options])
fs.readFileSync(path[, options])
fs.readlinkSync(path[, options])
fs.readSync(fd, buffer, offset, length[, position])
fs.readSync(fd, buffer[, options])
fs.readvSync(fd, buffers[, position])
fs.realpathSync(path[, options])
fs.realpathSync.native(path[, options])
fs.renameSync(oldPath, newPath)
fs.rmdirSync(path[, options])
fs.rmSync(path[, options])
fs.statSync(path[, options])
fs.statfsSync(path[, options])
fs.symlinkSync(target, path[, type])
fs.truncateSync(path[, len])
fs.unlinkSync(path)
fs.utimesSync(path, atime, mtime)
fs.writeFileSync(file, data[, options])
fs.writeSync(fd, buffer, offset[, length[, position]])
fs.writeSync(fd, buffer[, options])
fs.writeSync(fd, string[, position[, encoding]])
fs.writevSync(fd, buffers[, position])
Common Objects
Class:
fs.Dir
dir.close()
dir.close(callback)
dir.closeSync()
dir.path
dir.read()
dir.read(callback)
dir.readSync()
dir[Symbol.asyncIterator]()
dir[Symbol.asyncDispose]()
dir[Symbol.dispose]()
Class:
fs.Dirent
dirent.isBlockDevice()
dirent.isCharacterDevice()
dirent.isDirectory()
dirent.isFIFO()
dirent.isFile()
dirent.isSocket()
dirent.isSymbolicLink()
dirent.name
dirent.parentPath
Class:
fs.FSWatcher
Event:
'change'
Event:
'close'
Event:
'error'
watcher.close()
watcher.ref()
watcher.unref()
Class:
fs.StatWatcher
watcher.ref()
watcher.unref()
Class:
fs.ReadStream
Event:
'close'
Event:
'open'
Event:
'ready'
readStream.bytesRead
readStream.path
readStream.pending
Class:
fs.Stats
stats.isBlockDevice()
stats.isCharacterDevice()
stats.isDirectory()
stats.isFIFO()
stats.isFile()
stats.isSocket()
stats.isSymbolicLink()
stats.dev
stats.ino
stats.mode
stats.nlink
stats.uid
stats.gid
stats.rdev
stats.size
stats.blksize
stats.blocks
stats.atimeMs
stats.mtimeMs
stats.ctimeMs
stats.birthtimeMs
stats.atimeNs
stats.mtimeNs
stats.ctimeNs
stats.birthtimeNs
stats.atime
stats.mtime
stats.ctime
stats.birthtime
Stat time values
Class:
fs.StatFs
statfs.bavail
statfs.bfree
statfs.blocks
statfs.bsize
statfs.ffree
statfs.files
statfs.type
Class:
fs.Utf8Stream
Event:
'close'
Event:
'drain'
Event:
'drop'
Event:
'error'
Event:
'finish'
Event:
'ready'
Event:
'write'
new fs.Utf8Stream([options])
utf8Stream.append
utf8Stream.contentMode
utf8Stream.destroy()
utf8Stream.end()
utf8Stream.fd
utf8Stream.file
utf8Stream.flush(callback)
utf8Stream.flushSync()
utf8Stream.fsync
utf8Stream.maxLength
utf8Stream.minLength
utf8Stream.mkdir
utf8Stream.mode
utf8Stream.periodicFlush
utf8Stream.reopen(file)
utf8Stream.sync
utf8Stream.write(data)
utf8Stream.writing
utf8Stream[Symbol.dispose]()
Class:
fs.WriteStream
Event:
'close'
Event:
'open'
Event:
'ready'
writeStream.bytesWritten
writeStream.close([callback])
writeStream.path
writeStream.pending
fs.constants
FS constants
File access constants
File copy constants
File open constants
File type constants
File mode constants
Notes
Ordering of callback and promise-based operations
File paths
String paths
File URL paths
Platform-specific considerations
Buffer paths
Per-drive working directories on Windows
File descriptors
Threadpool usage
File system flags
File system
Source Code:
lib/fs.js
Stability: 2
- Stable
The
node:fs
module enables interacting with the file system in a
way modeled on standard POSIX functions.
To use the promise-based APIs:
import
as
fs
from
'node:fs/promises'
const
fs
require
'node:fs/promises'
To use the callback and sync APIs:
import
as
fs
from
'node:fs'
const
fs
require
'node:fs'
All file system operations have synchronous, callback, and promise-based
forms, and are accessible using both CommonJS syntax and ES6 Modules (ESM).
Promise example
Promise-based operations return a promise that is fulfilled when the
asynchronous operation is complete.
import
unlink
from
'node:fs/promises'
try
await
unlink
'/tmp/hello'
console
log
'successfully deleted /tmp/hello'
catch
(error)
console
error
'there was an error:'
error
message)
const
unlink
require
'node:fs/promises'
async
function
path
try
await
unlink
(path)
console
log
`successfully deleted
${
path
catch
(error)
console
error
'there was an error:'
error
message)
)(
'/tmp/hello'
Callback example
The callback form takes a completion callback function as its last
argument and invokes the operation asynchronously. The arguments passed to
the completion callback depend on the method, but the first argument is always
reserved for an exception. If the operation is completed successfully, then
the first argument is
null
or
undefined
import
unlink
from
'node:fs'
unlink
'/tmp/hello'
err
=>
if
(err)
throw
err
console
log
'successfully deleted /tmp/hello'
const
unlink
require
'node:fs'
unlink
'/tmp/hello'
err
=>
if
(err)
throw
err
console
log
'successfully deleted /tmp/hello'
The callback-based versions of the
node:fs
module APIs are preferable over
the use of the promise APIs when maximal performance (both in terms of
execution time and memory allocation) is required.
Synchronous example
The synchronous APIs block the Node.js event loop and further JavaScript
execution until the operation is complete. Exceptions are thrown immediately
and can be handled using
try…catch
, or can be allowed to bubble up.
import
unlinkSync
from
'node:fs'
try
unlinkSync
'/tmp/hello'
console
log
'successfully deleted /tmp/hello'
catch
(err)
// handle the error
const
unlinkSync
require
'node:fs'
try
unlinkSync
'/tmp/hello'
console
log
'successfully deleted /tmp/hello'
catch
(err)
// handle the error
Promises API
Added in: v10.0.0
History
Version
Changes
v14.0.0
Exposed as
require('fs/promises')
v11.14.0, v10.17.0
This API is no longer experimental.
v10.1.0
The API is accessible via
require('fs').promises
only.
The
fs/promises
API provides asynchronous file system methods that return
promises.
The promise APIs use the underlying Node.js threadpool to perform file
system operations off the event loop thread. These operations are not
synchronized or threadsafe. Care must be taken when performing multiple
concurrent modifications on the same file or data corruption may occur.
Class:
FileHandle
Added in: v10.0.0

object is an object wrapper for a numeric file descriptor.
Instances of the

object are created by the
fsPromises.open()
method.
All

objects are

s.
If a

is not closed using the
filehandle.close()
method, it will
try to automatically close the file descriptor and emit a process warning,
helping to prevent memory leaks. Please do not rely on this behavior because
it can be unreliable and the file may not be closed. Instead, always explicitly
close

s. Node.js may change this behavior in the future.
Event:
'close'
Added in: v15.4.0
The
'close'
event is emitted when the

has been closed and can no
longer be used.
filehandle.appendFile(data[, options])
Added in: v10.0.0
History
Version
Changes
v21.1.0, v20.10.0
The
flush
option is now supported.
v15.14.0, v14.18.0
The
data
argument supports
AsyncIterable
Iterable
, and
Stream
v14.0.0
The
data
parameter won't coerce unsupported input to strings anymore.
data







options


encoding


Default:
'utf8'
signal


allows aborting an in-progress writeFile.
Default:
undefined
Returns:

Fulfills with
undefined
upon success.
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()
filehandle.chmod(mode)
Added in: v10.0.0
mode

the file mode bit mask.
Returns:

Fulfills with
undefined
upon success.
Modifies the permissions on the file. See
chmod(2)
filehandle.chown(uid, gid)
Added in: v10.0.0
uid

The file's new owner's user id.
gid

The file's new group's group id.
Returns:

Fulfills with
undefined
upon success.
Changes the ownership of the file. A wrapper for
chown(2)
filehandle.close()
Added in: v10.0.0
Returns:

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
()
filehandle.createReadStream([options])
Added in: v16.11.0
options

encoding

Default:
null
autoClose

Default:
true
emitClose

Default:
true
start

end

Default:
Infinity
highWaterMark

Default:
64 * 1024
signal


Default:
undefined
Returns:

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

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
},
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
filehandle.createWriteStream([options])
Added in: v16.11.0
History
Version
Changes
v21.0.0, v20.10.0
The
flush
option is now supported.
options

encoding

Default:
'utf8'
autoClose

Default:
true
emitClose

Default:
true
start

highWaterMark

Default:
16384
flush

If
true
, the underlying file descriptor is flushed
prior to closing it.
Default:
false
Returns:

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
. The
encoding
can be any one of those accepted by

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.
filehandle.datasync()
Added in: v10.0.0
Returns:

Fulfills with
undefined
upon success.
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.
filehandle.fd
Added in: v10.0.0
Type:

The numeric file descriptor managed by the

object.
filehandle.pull([...transforms][, options])
Added in: v25.9.0
Stability: 1 - Experimental
...transforms


Optional transforms to apply via
stream/iter pull()
options

signal

autoClose

Close the file handle when the stream ends.
Default:
false
start

Byte offset to begin reading from. When specified,
reads use explicit positioning (
pread
semantics).
Default:
current
file position.
limit

Maximum number of bytes to read before ending the
iterator. Reads stop when
limit
bytes have been delivered or EOF is
reached, whichever comes first.
Default:
read until EOF.
chunkSize

Size in bytes of the buffer allocated for each
read operation.
Default:
131072
(128 KB).
Returns: {AsyncIterable}
Return the file contents as an async iterable using the
node:stream/iter
pull model. Reads are performed in
chunkSize
-byte
chunks (default 128 KB). If transforms are provided, they are applied
via
stream/iter pull()
The file handle is locked while the iterable is being consumed and unlocked
when iteration completes, an error occurs, or the consumer breaks.
This function is only available when the
--experimental-stream-iter
flag is
enabled.
import
open
from
'node:fs/promises'
import
text
from
'node:stream/iter'
import
compressGzip
from
'node:zlib/iter'
const
fh
await
open
'input.txt'
'r'
// Read as text
console
log
await
text
(fh
pull
autoClose
true
)))
// Read 1 KB starting at byte 100
const
fh2
await
open
'input.txt'
'r'
console
log
await
text
(fh2
pull
start
100
limit
1024
autoClose
true
)))
// Read with compression
const
fh3
await
open
'input.txt'
'r'
const
compressed
fh3
pull
compressGzip
()
autoClose
true
const
open
require
'node:fs/promises'
const
text
require
'node:stream/iter'
const
compressGzip
require
'node:zlib/iter'
async
function
run
()
const
fh
await
open
'input.txt'
'r'
// Read as text
console
log
await
text
(fh
pull
autoClose
true
)))
// Read 1 KB starting at byte 100
const
fh2
await
open
'input.txt'
'r'
console
log
await
text
(fh2
pull
start
100
limit
1024
autoClose
true
)))
// Read with compression
const
fh3
await
open
'input.txt'
'r'
const
compressed
fh3
pull
compressGzip
()
autoClose
true
run
()
catch
(console
error)
filehandle.pullSync([...transforms][, options])
Added in: v25.9.0
Stability: 1 - Experimental
...transforms


Optional transforms to apply via
stream/iter pullSync()
options

autoClose

Close the file handle when the stream ends.
Default:
false
start

Byte offset to begin reading from. When specified,
reads use explicit positioning.
Default:
current file position.
limit

Maximum number of bytes to read before ending the
iterator.
Default:
read until EOF.
chunkSize

Size in bytes of the buffer allocated for each
read operation.
Default:
131072
(128 KB).
Returns: {Iterable}
Synchronous counterpart of
filehandle.pull()
. Returns a sync iterable
that reads the file using synchronous I/O on the main thread. Reads are
performed in
chunkSize
-byte chunks (default 128 KB).
The file handle is locked while the iterable is being consumed. Unlike the
async
pull()
, this method does not support
AbortSignal
since all
operations are synchronous.
This function is only available when the
--experimental-stream-iter
flag is
enabled.
import
open
from
'node:fs/promises'
import
textSync
pipeToSync
from
'node:stream/iter'
import
compressGzipSync
decompressGzipSync
from
'node:zlib/iter'
const
fh
await
open
'input.txt'
'r'
// Read as text (sync)
console
log
textSync
(fh
pullSync
autoClose
true
)))
// Sync compress pipeline: file -> gzip -> file
const
src
await
open
'input.txt'
'r'
const
dst
await
open
'output.gz'
'w'
pipeToSync
(src
pullSync
compressGzipSync
()
autoClose
true
dst
writer
autoClose
true
))
const
open
require
'node:fs/promises'
const
textSync
pipeToSync
require
'node:stream/iter'
const
compressGzipSync
decompressGzipSync
require
'node:zlib/iter'
async
function
run
()
const
fh
await
open
'input.txt'
'r'
// Read as text (sync)
console
log
textSync
(fh
pullSync
autoClose
true
)))
// Sync compress pipeline: file -> gzip -> file
const
src
await
open
'input.txt'
'r'
const
dst
await
open
'output.gz'
'w'
pipeToSync
src
pullSync
compressGzipSync
()
autoClose
true
dst
writer
autoClose
true
run
()
catch
(console
error)
filehandle.read(buffer, offset, length, position)
Added in: v10.0.0
History
Version
Changes
v21.0.0
Accepts bigint values as
position
buffer



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

The location in the buffer at which to start filling.
Default:
length

The number of bytes to read.
Default:
buffer.byteLength - offset
position



The location where to begin reading data
from the file. If
null
or
-1
, data will be read from the current file
position, and the position will be updated. If
position
is a non-negative
integer, the current file position will remain unchanged.
Default:
null
Returns:

Fulfills upon success with an object with two properties:
bytesRead

The number of bytes read
buffer



A reference to the passed in
buffer
argument.
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.
filehandle.read([options])
Added in: v13.11.0, v12.17.0
History
Version
Changes
v21.0.0
Accepts bigint values as
position
options

buffer



A buffer that will be filled with the
file data read.
Default:
Buffer.alloc(16384)
offset

The location in the buffer at which to start filling.
Default:
length

The number of bytes to read.
Default:
buffer.byteLength - offset
position



The location where to begin reading data
from the file. If
null
or
-1
, data will be read from the current file
position, and the position will be updated. If
position
is a non-negative
integer, the current file position will remain unchanged.
Default:
null
Returns:

Fulfills upon success with an object with two properties:
bytesRead

The number of bytes read
buffer



A reference to the passed in
buffer
argument.
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.
filehandle.read(buffer[, options])
Added in: v18.2.0, v16.17.0
History
Version
Changes
v21.0.0
Accepts bigint values as
position
buffer



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

offset

The location in the buffer at which to start filling.
Default:
length

The number of bytes to read.
Default:
buffer.byteLength - offset
position



The location where to begin reading data
from the file. If
null
or
-1
, data will be read from the current file
position, and the position will be updated. If
position
is a non-negative
integer, the current file position will remain unchanged.
Default:
null
Returns:

Fulfills upon success with an object with two properties:
bytesRead

The number of bytes read
buffer



A reference to the passed in
buffer
argument.
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.
filehandle.readableWebStream([options])
Added in: v17.0.0
History
Version
Changes
v24.0.0, v22.17.0
Marking the API stable.
v23.8.0, v22.15.0
Removed option to create a 'bytes' stream. Streams are now always 'bytes' streams.
v20.0.0, v18.17.0
Added option to create a 'bytes' stream.
options

autoClose

When true, causes the

to be closed when the
stream is closed.
Default:
false
Returns:

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
()
const
open
require
'node:fs/promises'
async
()
=>
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 the
fileHandle.close()
method unless the
autoClose
option is set to
true
filehandle.readFile(options)
Added in: v10.0.0
options


encoding


Default:
null
signal

allows aborting an in-progress readFile
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

object. Otherwise, the data will be a string.
Asynchronously reads the entire contents of a file.
If
options
is a string, then it specifies the
encoding
The

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.
filehandle.readLines([options])
Added in: v18.11.0
options

encoding

Default:
null
autoClose

Default:
true
emitClose

Default:
true
start

end

Default:
Infinity
highWaterMark

Default:
64 * 1024
Returns:

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)
const
open
require
'node:fs/promises'
async
()
=>
const
file
await
open
'./some/file/to/read'
for
await
const
line
of
file
readLines
())
console
log
(line)
)()
filehandle.readv(buffers[, position])
Added in: v13.13.0, v12.17.0
buffers



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.
Default:
null
Returns:

Fulfills upon success an object containing two properties:
bytesRead

the number of bytes read
buffers



property containing
a reference to the
buffers
input.
Read from a file and write to an array of

filehandle.stat([options])
Added in: v10.0.0
History
Version
Changes
v10.5.0
Accepts an additional
options
object to specify whether the numeric values returned should be bigint.
options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
Returns:

Fulfills with an

for the file.
filehandle.sync()
Added in: v10.0.0
Returns:

Fulfills with
undefined
upon success.
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.
filehandle.truncate(len)
Added in: v10.0.0
len

Default:
Returns:

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
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
will be used.
filehandle.utimes(atime, mtime)
Added in: v10.0.0
atime



mtime



Returns:

Change the file system timestamps of the object referenced by the

then fulfills the promise with no arguments upon success.
filehandle.write(buffer, offset[, length[, position]])
Added in: v10.0.0
History
Version
Changes
v14.0.0
The
buffer
parameter won't coerce unsupported input to buffers anymore.
buffer



offset

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

The number of bytes from
buffer
to write.
Default:
buffer.byteLength - offset
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.
Default:
null
Returns:

Write
buffer
to the file.
The promise is fulfilled with an object containing two properties:
bytesWritten

the number of bytes written
buffer



a reference to the
buffer
written.
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.
filehandle.write(buffer[, options])
Added in: v18.3.0, v16.17.0
buffer



options

offset

Default:
length

Default:
buffer.byteLength - offset
position


Default:
null
Returns:

Write
buffer
to the file.
Similar to the above
filehandle.write
function, this version takes an
optional
options
object. If no
options
object is specified, it will
default with the above values.
filehandle.write(string[, position[, encoding]])
Added in: v10.0.0
History
Version
Changes
v14.0.0
The
string
parameter won't coerce unsupported input to strings anymore.
string

position


The offset from the beginning of the file where the
data from
string
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.
Default:
null
encoding

The expected string encoding.
Default:
'utf8'
Returns:

Write
string
to the file. If
string
is not a string, the promise is
rejected with an error.
The promise is fulfilled with an object containing two properties:
bytesWritten

the number of bytes written
buffer

a reference to the
string
written.
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.
filehandle.writeFile(data, options)
Added in: v10.0.0
History
Version
Changes
v15.14.0, v14.18.0
The
data
argument supports
AsyncIterable
Iterable
, and
Stream
v14.0.0
The
data
parameter won't coerce unsupported input to strings anymore.
data







options


encoding


The expected character encoding when
data
is a
string.
Default:
'utf8'
signal


allows aborting an in-progress writeFile.
Default:
undefined
Returns:

Asynchronously writes data to a file, replacing the file if it already exists.
data
can be a string, a buffer, an

, or an

object.
The promise is fulfilled with no arguments upon success.
If
options
is a string, then it specifies the
encoding
The

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 a
filehandle.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.
filehandle.writev(buffers[, position])
Added in: v12.9.0
buffers



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.
Default:
null
Returns:

Write an array of

s to the file.
The promise is fulfilled with an object containing a two properties:
bytesWritten

the number of bytes written
buffers



a reference to the
buffers
input.
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.
filehandle.writer([options])
Added in: v25.9.0
Stability: 1 - Experimental
options

autoClose

Close the file handle when the writer ends or
fails.
Default:
false
start

Byte offset to start writing at. When specified,
writes use explicit positioning.
Default:
current file position.
limit

Maximum number of bytes the writer will accept.
Async writes (
write()
writev()
) that would exceed the limit reject
with
ERR_OUT_OF_RANGE
. Sync writes (
writeSync()
writevSync()
return
false
Default:
no limit.
chunkSize

Maximum chunk size in bytes for synchronous write
operations. Writes larger than this threshold fall back to async I/O.
Set this to match the reader's
chunkSize
for optimal
pipeTo()
performance.
Default:
131072
(128 KB).
Returns:

write(chunk[, options])

Returns {Promise
}.
Accepts
Uint8Array
Buffer
, or string (UTF-8 encoded).
chunk




options

signal

If the signal is already aborted, the write
rejects with
AbortError
without performing I/O.
writev(chunks[, options])

Returns {Promise
}. Uses
scatter/gather I/O via a single
writev()
syscall. Accepts mixed
Uint8Array
/string arrays.
chunks
{Array}
options

signal

If the signal is already aborted, the write
rejects with
AbortError
without performing I/O.
writeSync(chunk)

Returns

. Attempts a synchronous
write. Returns
true
if the write succeeded,
false
if the caller
should fall back to async
write()
. Returns
false
when: the writer
is closed/errored, an async operation is in flight, the chunk exceeds
chunkSize
, or the write would exceed
limit
chunk




writevSync(chunks)

Returns

. Synchronous batch
write. Same fallback semantics as
writeSync()
chunks
{Array}
end([options])

Returns {Promise
} total bytes
written. Idempotent: returns
totalBytesWritten
if already closed,
returns the pending promise if already closing. Rejects if the writer
is in an errored state.
options

signal

If the signal is already aborted,
end()
rejects with
AbortError
and the writer remains open.
endSync()

Returns


total bytes written on
success,
-1
if the writer is errored or an async operation is in
flight. Idempotent when already closed.
fail(reason)

Puts the writer into a terminal error state.
Synchronous. If the writer is already closed or errored, this is a
no-op. If
autoClose
is true, closes the file handle synchronously.
Return a
node:stream/iter
writer backed by this file handle.
The writer supports both
Symbol.asyncDispose
and
Symbol.dispose
await using w = fh.writer()
— if the writer is still open (no
end()
called),
asyncDispose
calls
fail()
. If
end()
is pending, it waits
for it to complete.
using w = fh.writer()
— calls
fail()
unconditionally.
The
writeSync()
and
writevSync()
methods enable the try-sync fast path
used by
stream/iter pipeTo()
. When the reader's chunk size matches the
writer's
chunkSize
, all writes in a
pipeTo()
pipeline complete
synchronously with zero promise overhead.
This function is only available when the
--experimental-stream-iter
flag is
enabled.
import
open
from
'node:fs/promises'
import
from
pipeTo
from
'node:stream/iter'
import
compressGzip
from
'node:zlib/iter'
// Async pipeline
const
fh
await
open
'output.gz'
'w'
await
pipeTo
from
'Hello!'
compressGzip
()
fh
writer
autoClose
true
))
// Sync pipeline with limit
const
src
await
open
'input.txt'
'r'
const
dst
await
open
'output.txt'
'w'
const
dst
writer
limit
1024
1024
// Max 1 MB
await
pipeTo
(src
pull
autoClose
true
w)
await
end
()
await
dst
close
()
const
open
require
'node:fs/promises'
const
from
pipeTo
require
'node:stream/iter'
const
compressGzip
require
'node:zlib/iter'
async
function
run
()
// Async pipeline
const
fh
await
open
'output.gz'
'w'
await
pipeTo
from
'Hello!'
compressGzip
()
fh
writer
autoClose
true
))
// Sync pipeline with limit
const
src
await
open
'input.txt'
'r'
const
dst
await
open
'output.txt'
'w'
const
dst
writer
limit
1024
1024
// Max 1 MB
await
pipeTo
(src
pull
autoClose
true
w)
await
end
()
await
dst
close
()
run
()
catch
(console
error)
filehandle[Symbol.asyncDispose]()
Added in: v20.4.0, v18.18.0
History
Version
Changes
v24.2.0
No longer experimental.
Calls
filehandle.close()
and returns a promise that fulfills when the
filehandle is closed.
fsPromises.access(path[, mode])
Added in: v10.0.0
path



mode

Default:
fs.constants.F_OK
Returns:

Fulfills with
undefined
upon success.
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

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.
fsPromises.appendFile(path, data[, options])
Added in: v10.0.0
History
Version
Changes
v21.1.0, v20.10.0
The
flush
option is now supported.
path




filename or

data


options


encoding


Default:
'utf8'
mode

Default:
0o666
flag

See
support of file system
flags
Default:
'a'
flush

If
true
, the underlying file descriptor is flushed
prior to closing it.
Default:
false
Returns:

Fulfills with
undefined
upon success.
Asynchronously append data to a file, creating the file if it does not yet
exist.
data
can be a string or a

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

that has been opened
for appending (using
fsPromises.open()
).
fsPromises.chmod(path, mode)
Added in: v10.0.0
path



mode


Returns:

Fulfills with
undefined
upon success.
Changes the permissions of a file.
fsPromises.chown(path, uid, gid)
Added in: v10.0.0
path



uid

gid

Returns:

Fulfills with
undefined
upon success.
Changes the ownership of a file.
fsPromises.copyFile(src, dest[, mode])
Added in: v10.0.0
History
Version
Changes
v14.0.0
Changed
flags
argument to
mode
and imposed stricter type validation.
src



source filename to copy
dest



destination filename of the copy operation
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
Default:
fs.constants.COPYFILE_EXCL
: The copy operation will fail if
dest
already exists.
fs.constants.COPYFILE_FICLONE
: The copy operation will attempt to create
a copy-on-write reflink. If the platform does not support copy-on-write,
then a fallback copy mechanism is used.
fs.constants.COPYFILE_FICLONE_FORCE
: The copy operation will attempt to
create a copy-on-write reflink. If the platform does not support
copy-on-write, then the operation will fail.
Returns:

Fulfills with
undefined
upon success.
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'
fsPromises.cp(src, dest[, options])
Added in: v16.7.0
History
Version
Changes
v22.3.0
This API is no longer experimental.
v20.1.0, v18.17.0
Accept an additional
mode
option to specify the copy behavior as the
mode
argument of
fs.copyFile()
v17.6.0, v16.15.0
Accepts an additional
verbatimSymlinks
option to specify whether to perform path resolution for symlinks.
src


source path to copy.
dest


destination path to copy to.
options

dereference

dereference symlinks.
Default:
false
errorOnExist

when
force
is
false
, and the destination
exists, throw an error.
Default:
false
filter

Function to filter copied files/directories. Return
true
to copy the item,
false
to ignore it. When ignoring a directory,
all of its contents will be skipped as well. Can also return a
Promise
that resolves to
true
or
false
Default:
undefined
src

source path to copy.
dest

destination path to copy to.
Returns:


A value that is coercible to
boolean
or
Promise
that fulfils with such value.
force

overwrite existing file or directory. The copy
operation will ignore errors if you set this to false and the destination
exists. Use the
errorOnExist
option to change this behavior.
Default:
true
mode

modifiers for copy operation.
Default:
See
mode
flag of
fsPromises.copyFile()
preserveTimestamps

When
true
timestamps from
src
will
be preserved.
Default:
false
recursive

copy directories recursively
Default:
false
verbatimSymlinks

When
true
, path resolution for symlinks will
be skipped.
Default:
false
Returns:

Fulfills with
undefined
upon success.
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/
fsPromises.glob(pattern[, options])
Added in: v22.0.0
History
Version
Changes
v24.1.0, v22.17.0
Add support for
URL
instances for
cwd
option.
v24.0.0, v22.17.0
Marking the API stable.
v23.7.0, v22.14.0
Add support for
exclude
option to accept glob patterns.
v22.2.0
Add support for
withFileTypes
as an option.
pattern


options

cwd


current working directory.
Default:
process.cwd()
exclude


Function to filter out files/directories or a
list of glob patterns to be excluded. If a function is provided, return
true
to exclude the item,
false
to include it.
Default:
undefined
If a string array is provided, each string should be a glob pattern that
specifies paths to exclude. Note: Negation patterns (e.g., '!foo.js') are
not supported.
withFileTypes

true
if the glob should return paths as Dirents,
false
otherwise.
Default:
false
Returns:

An AsyncIterator that yields the paths of files
that match the pattern.
import
glob
from
'node:fs/promises'
for
await
const
entry
of
glob
'**/*.js'
))
console
log
(entry)
const
glob
require
'node:fs/promises'
async
()
=>
for
await
const
entry
of
glob
'**/*.js'
))
console
log
(entry)
)()
fsPromises.lchmod(path, mode)
Deprecated in: v10.0.0
Stability: 0 - Deprecated
path



mode

Returns:

Fulfills with
undefined
upon success.
Changes the permissions on a symbolic link.
This method is only implemented on macOS.
fsPromises.lchown(path, uid, gid)
Added in: v10.0.0
History
Version
Changes
v10.6.0
This API is no longer deprecated.
path



uid

gid

Returns:

Fulfills with
undefined
upon success.
Changes the ownership on a symbolic link.
fsPromises.lutimes(path, atime, mtime)
Added in: v14.5.0, v12.19.0
path



atime



mtime



Returns:

Fulfills with
undefined
upon success.
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.
fsPromises.link(existingPath, newPath)
Added in: v10.0.0
existingPath



newPath



Returns:

Fulfills with
undefined
upon success.
Creates a new link from the
existingPath
to the
newPath
. See the POSIX
link(2)
documentation for more detail.
fsPromises.lstat(path[, options])
Added in: v10.0.0
History
Version
Changes
v10.5.0
Accepts an additional
options
object to specify whether the numeric values returned should be bigint.
path



options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
Returns:

Fulfills with the

object for the given
symbolic link
path
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.
fsPromises.mkdir(path[, options])
Added in: v10.0.0
path



options


recursive

Default:
false
mode


Not supported on Windows. See
File modes
for more details.
Default:
0o777
Returns:

Upon success, fulfills with
undefined
if
recursive
is
false
, or the first directory path created if
recursive
is
true
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)
const
mkdir
require
'node:fs/promises'
const
join
require
'node:path'
async
function
makeDirectory
()
const
projectFolder
join
(__dirname
'test'
'project'
const
dirCreation
await
mkdir
(projectFolder
recursive
true
console
log
(dirCreation)
return
dirCreation
makeDirectory
()
catch
(console
error)
fsPromises.mkdtemp(prefix[, options])
Added in: v10.0.0
History
Version
Changes
v20.6.0, v18.19.0
The
prefix
parameter now accepts buffers and URL.
v16.5.0, v14.18.0
The
prefix
parameter now accepts an empty string.
prefix



options


encoding

Default:
'utf8'
Returns:

Fulfills with a string containing the file system path
of the newly created temporary 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
characters in
prefix
. Some
platforms, notably the BSDs, can return more than six random characters, and
replace trailing
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
require('node:path').sep
).
fsPromises.mkdtempDisposable(prefix[, options])
Added in: v24.4.0
prefix



options


encoding

Default:
'utf8'
Returns:

Fulfills with a Promise for an async-disposable Object:
path

The path of the created directory.
remove

A function which removes the created directory.
[Symbol.asyncDispose]

The same as
remove
The resulting Promise holds an async-disposable object whose
path
property
holds the created directory path. When the object is disposed, the directory
and its contents will be removed asynchronously if it still exists. If the
directory cannot be deleted, disposal will throw an error. The object has an
async
remove()
method which will perform the same task.
Both this function and the disposal function on the resulting object are
async, so it should be used with
await
await using
as in
await using dir = await fsPromises.mkdtempDisposable('prefix')
For detailed information, see the documentation of
fsPromises.mkdtemp()
The optional
options
argument can be a string specifying an encoding, or an
object with an
encoding
property specifying the character encoding to use.
fsPromises.open(path, flags[, mode])
Added in: v10.0.0
History
Version
Changes
v11.1.0
The
flags
argument is now optional and defaults to
'r'
path



flags


See
support of file system
flags
Default:
'r'
mode


Sets the file mode (permission and sticky bits)
if the file is created. See
File modes
for more details.
Default:
0o666
(readable and writable)
Returns:

Fulfills with a

object.
Opens a

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
fsPromises.opendir(path[, options])
Added in: v12.12.0
History
Version
Changes
v20.1.0, v18.17.0
Added
recursive
option.
v13.1.0, v12.16.0
The
bufferSize
option was introduced.
path



options

encoding


Default:
'utf8'
bufferSize

Number of directory entries that are buffered
internally when reading from the directory. Higher values lead to better
performance but higher memory usage.
Default:
32
recursive

Resolved
Dir
will be an

containing all sub files and directories.
Default:
false
Returns:

Fulfills with an

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

, 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

object will be automatically
closed after the iterator exits.
fsPromises.readdir(path[, options])
Added in: v10.0.0
History
Version
Changes
v20.1.0, v18.17.0
Added
recursive
option.
v10.11.0
New option
withFileTypes
was added.
path



options


encoding

Default:
'utf8'
withFileTypes

Default:
false
recursive

If
true
, reads the contents of a directory
recursively. In recursive mode, it will list all files, sub files, and
directories.
Default:
false
Returns:

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

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

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)
fsPromises.readFile(path[, options])
Added in: v10.0.0
History
Version
Changes
v15.2.0, v14.17.0
The options argument may include an AbortSignal to abort an ongoing readFile request.
path




filename or
FileHandle
options


encoding


Default:
null
flag

See
support of file system
flags
Default:
'r'
signal

allows aborting an in-progress readFile
Returns:

Fulfills with the contents of the file.
Asynchronously reads the entire contents of a file.
If no encoding is specified (using
options.encoding
), the data is returned
as a

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)
const
readFile
require
'node:fs/promises'
const
resolve
require
'node:path'
async
function
logFile
()
try
const
filePath
resolve
'./package.json'
const
contents
await
readFile
(filePath
encoding
'utf8'
console
log
(contents)
catch
(err)
console
error
(err
message)
logFile
()
It is possible to abort an ongoing
readFile
using an

. 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

has to support reading.
fsPromises.readlink(path[, options])
Added in: v10.0.0
path



options


encoding

Default:
'utf8'
Returns:

Fulfills with the
linkString
upon success.
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 the
linkString
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

object.
fsPromises.realpath(path[, options])
Added in: v10.0.0
path



options


encoding

Default:
'utf8'
Returns:

Fulfills with the resolved path upon success.
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

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.
fsPromises.rename(oldPath, newPath)
Added in: v10.0.0
oldPath



newPath



Returns:

Fulfills with
undefined
upon success.
Renames
oldPath
to
newPath
fsPromises.rmdir(path[, options])
Added in: v10.0.0
History
Version
Changes
v25.0.0
Remove
recursive
option.
v16.0.0
Using
fsPromises.rmdir(path, { recursive: true })
on a
path
that is a file is no longer permitted and results in an
ENOENT
error on Windows and an
ENOTDIR
error on POSIX.
v16.0.0
Using
fsPromises.rmdir(path, { recursive: true })
on a
path
that does not exist is no longer permitted and results in a
ENOENT
error.
v16.0.0
The
recursive
option is deprecated, using it triggers a deprecation warning.
v14.14.0
The
recursive
option is deprecated, use
fsPromises.rm
instead.
v13.3.0, v12.16.0
The
maxBusyTries
option is renamed to
maxRetries
, and its default is 0. The
emfileWait
option has been removed, and
EMFILE
errors use the same retry logic as other errors. The
retryDelay
option is now supported.
ENFILE
errors are now retried.
v12.10.0
The
recursive
maxBusyTries
, and
emfileWait
options are now supported.
path



options

There are currently no options exposed. There used to
be options for
recursive
maxBusyTries
, and
emfileWait
but they were
deprecated and removed. The
options
argument is still accepted for
backwards compatibility but it is not used.
Returns:

Fulfills with
undefined
upon success.
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 }
fsPromises.rm(path[, options])
Added in: v14.14.0
path



options

force

When
true
, exceptions will be ignored if
path
does
not exist.
Default:
false
maxRetries

If an
EBUSY
EMFILE
ENFILE
ENOTEMPTY
, or
EPERM
error is encountered, Node.js will retry the operation with a linear
backoff wait of
retryDelay
milliseconds longer on each try. This option
represents the number of retries. This option is ignored if the
recursive
option is not
true
Default:
recursive

If
true
, perform a recursive directory removal. In
recursive mode operations are retried on failure.
Default:
false
retryDelay

The amount of time in milliseconds to wait between
retries. This option is ignored if the
recursive
option is not
true
Default:
100
Returns:

Fulfills with
undefined
upon success.
Removes files and directories (modeled on the standard POSIX
rm
utility).
fsPromises.stat(path[, options])
Added in: v10.0.0
History
Version
Changes
v25.7.0
Accepts a
throwIfNoEntry
option to specify whether an exception should be thrown if the entry does not exist.
v10.5.0
Accepts an additional
options
object to specify whether the numeric values returned should be bigint.
path



options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
throwIfNoEntry

Whether an exception will be thrown
if no file system entry exists, rather than returning
undefined
Default:
true
Returns:

Fulfills with the

object for the
given
path
fsPromises.statfs(path[, options])
Added in: v19.6.0, v18.15.0
path



options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
Returns:

Fulfills with the

object for the
given
path
fsPromises.symlink(target, path[, type])
Added in: v10.0.0
History
Version
Changes
v19.0.0
If the
type
argument is
null
or omitted, Node.js will autodetect
target
type and automatically select
dir
or
file
target



path



type


Default:
null
Returns:

Fulfills with
undefined
upon success.
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
null
, 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.
fsPromises.truncate(path[, len])
Added in: v10.0.0
path



len

Default:
Returns:

Fulfills with
undefined
upon success.
Truncates (shortens or extends the length) of the content at
path
to
len
bytes.
fsPromises.unlink(path)
Added in: v10.0.0
path



Returns:

Fulfills with
undefined
upon success.
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.
fsPromises.utimes(path, atime, mtime)
Added in: v10.0.0
path



atime



mtime



Returns:

Fulfills with
undefined
upon success.
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,
Date
s, 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.
fsPromises.watch(filename[, options])
Added in: v15.9.0, v14.18.0
filename



options


persistent

Indicates whether the process should continue to run
as long as files are being watched.
Default:
true
recursive

Indicates whether all subdirectories should be
watched, or only the current directory. This applies when a directory is
specified, and only on supported platforms (See
caveats
).
Default:
false
encoding

Specifies the character encoding to be used for the
filename passed to the listener.
Default:
'utf8'
signal

An

used to signal when the watcher
should stop.
maxQueue

Specifies the number of events to queue between iterations
of the

returned.
Default:
2048
overflow

Either
'ignore'
or
'throw'
when there are more events to be
queued than
maxQueue
allows.
'ignore'
means overflow events are dropped and a
warning is emitted, while
'throw'
means to throw an exception.
Default:
'ignore'
ignore




Pattern(s) to ignore. Strings are
glob patterns (using
minimatch
), RegExp patterns are tested against
the filename, and functions receive the filename and return
true
to
ignore.
Default:
undefined
Returns:

of objects with the properties:
eventType

The type of change
filename



The name of the file changed.
Returns an async iterator that watches for changes on
filename
, where
filename
is either a file or a directory.
const
watch
require
'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()
fsPromises.writeFile(file, data[, options])
Added in: v10.0.0
History
Version
Changes
v21.0.0, v20.10.0
The
flush
option is now supported.
v15.14.0, v14.18.0
The
data
argument supports
AsyncIterable
Iterable
, and
Stream
v15.2.0, v14.17.0
The options argument may include an AbortSignal to abort an ongoing writeFile request.
v14.0.0
The
data
parameter won't coerce unsupported input to strings anymore.
file




filename or
FileHandle
data







options


encoding


Default:
'utf8'
mode

Default:
0o666
flag

See
support of file system
flags
Default:
'w'
flush

If all data is successfully written to the file, and
flush
is
true
filehandle.sync()
is used to flush the data.
Default:
false
signal

allows aborting an in-progress writeFile
Returns:

Fulfills with
undefined
upon success.
Asynchronously writes data to a file, replacing the file if it already exists.
data
can be a string, a buffer, an

, or an

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

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

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.
fsPromises.constants
Added in: v18.4.0, v16.17.0
Type:

Returns an object containing commonly used constants for file system
operations. The object is the same as
fs.constants
. See
FS constants
for more details.
Callback API
The callback APIs perform all operations asynchronously, without blocking the
event loop, then invoke a callback function upon completion or error.
The callback APIs use the underlying Node.js threadpool to perform file
system operations off the event loop thread. These operations are not
synchronized or threadsafe. Care must be taken when performing multiple
concurrent modifications on the same file or data corruption may occur.
fs.access(path[, mode], callback)
Added in: v0.11.15
History
Version
Changes
v25.0.0
The constants
fs.F_OK
fs.R_OK
fs.W_OK
and
fs.X_OK
which were present directly on
fs
are removed.
v20.8.0
The constants
fs.F_OK
fs.R_OK
fs.W_OK
and
fs.X_OK
which were present directly on
fs
are deprecated.
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v6.3.0
The constants like
fs.R_OK
, etc which were present directly on
fs
were moved into
fs.constants
as a soft deprecation. Thus for Node.js
< v6.3.0
use
fs
to access those constants, or do something like
(fs.constants || fs).R_OK
to work with all versions.
path



mode

Default:
fs.constants.F_OK
callback

err

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
The final argument,
callback
, is a callback function that is invoked with
a possible error argument. If any of the accessibility checks fail, the error
argument will be an
Error
object. The following examples check if
package.json
exists, and if it is readable or writable.
import
access
constants
from
'node:fs'
const
file
'package.json'
// Check if the file exists in the current directory.
access
(file
constants
F_OK
err
=>
console
log
${
file
${
err
'does not exist'
'exists'
// Check if the file is readable.
access
(file
constants
R_OK
err
=>
console
log
${
file
${
err
'is not readable'
'is readable'
// Check if the file is writable.
access
(file
constants
W_OK
err
=>
console
log
${
file
${
err
'is not writable'
'is writable'
// Check if the file is readable and writable.
access
(file
constants
R_OK
constants
W_OK
err
=>
console
log
${
file
${
err
'is not'
'is'
readable and writable`
Do not use
fs.access()
to check for the accessibility of a file before calling
fs.open()
fs.readFile()
, or
fs.writeFile()
. 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.
write (NOT RECOMMENDED)
import
access
open
close
from
'node:fs'
access
'myfile'
err
=>
if
err)
console
error
'myfile already exists'
return
open
'myfile'
'wx'
err
fd
=>
if
(err)
throw
err
try
writeMyData
(fd)
finally
close
(fd
err
=>
if
(err)
throw
err
write (RECOMMENDED)
import
open
close
from
'node:fs'
open
'myfile'
'wx'
err
fd
=>
if
(err)
if
(err
code
===
'EEXIST'
console
error
'myfile already exists'
return
throw
err
try
writeMyData
(fd)
finally
close
(fd
err
=>
if
(err)
throw
err
read (NOT RECOMMENDED)
import
access
open
close
from
'node:fs'
access
'myfile'
err
=>
if
(err)
if
(err
code
===
'ENOENT'
console
error
'myfile does not exist'
return
throw
err
open
'myfile'
'r'
err
fd
=>
if
(err)
throw
err
try
readMyData
(fd)
finally
close
(fd
err
=>
if
(err)
throw
err
read (RECOMMENDED)
import
open
close
from
'node:fs'
open
'myfile'
'r'
err
fd
=>
if
(err)
if
(err
code
===
'ENOENT'
console
error
'myfile does not exist'
return
throw
err
try
readMyData
(fd)
finally
close
(fd
err
=>
if
(err)
throw
err
The "not recommended" examples above check for accessibility and then use the
file; the "recommended" examples are better because they use the file directly
and handle the error, if any.
In general, check for the accessibility of a file only if the file will not be
used directly, for example when its accessibility is a signal from another
process.
On Windows, access-control policies (ACLs) on a directory may limit access to
a file or directory. The
fs.access()
function, however, does not check the
ACL and therefore may report that a path is accessible even if the ACL restricts
the user from reading or writing to it.
fs.appendFile(path, data[, options], callback)
Added in: v0.6.7
History
Version
Changes
v21.1.0, v20.10.0
The
flush
option is now supported.
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
v7.0.0
The passed
options
object will never be modified.
v5.0.0
The
file
parameter can be a file descriptor now.
path




filename or file descriptor
data


options


encoding


Default:
'utf8'
mode

Default:
0o666
flag

See
support of file system
flags
Default:
'a'
flush

If
true
, the underlying file descriptor is flushed
prior to closing it.
Default:
false
callback

err

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

The
mode
option only affects the newly created file. See
fs.open()
for more details.
import
appendFile
from
'node:fs'
appendFile
'message.txt'
'data to append'
err
=>
if
(err)
throw
err
console
log
'The "data to append" was appended to file!'
If
options
is a string, then it specifies the encoding:
import
appendFile
from
'node:fs'
appendFile
'message.txt'
'data to append'
'utf8'
callback)
The
path
may be specified as a numeric file descriptor that has been opened
for appending (using
fs.open()
or
fs.openSync()
). The file descriptor will
not be closed automatically.
import
open
close
appendFile
from
'node:fs'
function
closeFd
fd
close
(fd
err
=>
if
(err)
throw
err
open
'message.txt'
'a'
err
fd
=>
if
(err)
throw
err
try
appendFile
(fd
'data to append'
'utf8'
err
=>
closeFd
(fd)
if
(err)
throw
err
catch
(err)
closeFd
(fd)
throw
err
fs.chmod(path, mode, callback)
Added in: v0.1.30
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
path



mode


callback

err

Asynchronously changes the permissions of a file. No arguments other than a
possible exception are given to the completion callback.
See the POSIX
chmod(2)
documentation for more detail.
import
chmod
from
'node:fs'
chmod
'my_file.txt'
0o775
err
=>
if
(err)
throw
err
console
log
'The permissions for file "my_file.txt" have been changed!'
File modes
The
mode
argument used in both the
fs.chmod()
and
fs.chmodSync()
methods is a numeric bitmask created using a logical OR of the following
constants:
Constant
Octal
Description
fs.constants.S_IRUSR
0o400
read by owner
fs.constants.S_IWUSR
0o200
write by owner
fs.constants.S_IXUSR
0o100
execute/search by owner
fs.constants.S_IRGRP
0o40
read by group
fs.constants.S_IWGRP
0o20
write by group
fs.constants.S_IXGRP
0o10
execute/search by group
fs.constants.S_IROTH
0o4
read by others
fs.constants.S_IWOTH
0o2
write by others
fs.constants.S_IXOTH
0o1
execute/search by others
An easier method of constructing the
mode
is to use a sequence of three
octal digits (e.g.
765
). The left-most digit (
in the example), specifies
the permissions for the file owner. The middle digit (
in the example),
specifies permissions for the group. The right-most digit (
in the example),
specifies the permissions for others.
Number
Description
read, write, and execute
read and write
read and execute
read only
write and execute
write only
execute only
no permission
For example, the octal value
0o765
means:
The owner may read, write, and execute the file.
The group may read and write the file.
Others may read and execute the file.
When using raw numbers where file modes are expected, any value larger than
0o777
may result in platform-specific behaviors that are not supported to work
consistently. Therefore constants like
S_ISVTX
S_ISGID
, or
S_ISUID
are
not exposed in
fs.constants
Caveats: on Windows only the write permission can be changed, and the
distinction among the permissions of group, owner, or others is not
implemented.
fs.chown(path, uid, gid, callback)
Added in: v0.1.97
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
path



uid

gid

callback

err

Asynchronously changes owner and group of a file. No arguments other than a
possible exception are given to the completion callback.
See the POSIX
chown(2)
documentation for more detail.
fs.close(fd[, callback])
Added in: v0.0.2
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v15.9.0, v14.17.0
A default callback is now used if one is not provided.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
fd

callback

err

Closes the file descriptor. No arguments other than a possible exception are
given to the completion callback.
Calling
fs.close()
on any file descriptor (
fd
) that is currently in use
through any other
fs
operation may lead to undefined behavior.
See the POSIX
close(2)
documentation for more detail.
fs.copyFile(src, dest[, mode], callback)
Added in: v8.5.0
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v14.0.0
Changed
flags
argument to
mode
and imposed stricter type validation.
src



source filename to copy
dest



destination filename of the copy operation
mode

modifiers for copy operation.
Default:
callback

err

Asynchronously copies
src
to
dest
. By default,
dest
is overwritten if it
already exists. No arguments other than a possible exception are given to the
callback function. Node.js makes no guarantees about the atomicity of the copy
operation. If an error occurs after the destination file has been opened for
writing, Node.js will attempt to remove the destination.
mode
is an optional integer that specifies 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
).
fs.constants.COPYFILE_EXCL
: The copy operation will fail if
dest
already
exists.
fs.constants.COPYFILE_FICLONE
: The copy operation will attempt to create a
copy-on-write reflink. If the platform does not support copy-on-write, then a
fallback copy mechanism is used.
fs.constants.COPYFILE_FICLONE_FORCE
: The copy operation will attempt to
create a copy-on-write reflink. If the platform does not support
copy-on-write, then the operation will fail.
import
copyFile
constants
from
'node:fs'
function
callback
err
if
(err)
throw
err
console
log
'source.txt was copied to destination.txt'
// destination.txt will be created or overwritten by default.
copyFile
'source.txt'
'destination.txt'
callback)
// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.
copyFile
'source.txt'
'destination.txt'
constants
COPYFILE_EXCL
callback)
fs.cp(src, dest[, options], callback)
Added in: v16.7.0
History
Version
Changes
v22.3.0
This API is no longer experimental.
v20.1.0, v18.17.0
Accept an additional
mode
option to specify the copy behavior as the
mode
argument of
fs.copyFile()
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v17.6.0, v16.15.0
Accepts an additional
verbatimSymlinks
option to specify whether to perform path resolution for symlinks.
src


source path to copy.
dest


destination path to copy to.
options

dereference

dereference symlinks.
Default:
false
errorOnExist

when
force
is
false
, and the destination
exists, throw an error.
Default:
false
filter

Function to filter copied files/directories. Return
true
to copy the item,
false
to ignore it. When ignoring a directory,
all of its contents will be skipped as well. Can also return a
Promise
that resolves to
true
or
false
Default:
undefined
src

source path to copy.
dest

destination path to copy to.
Returns:


A value that is coercible to
boolean
or
Promise
that fulfils with such value.
force

overwrite existing file or directory. The copy
operation will ignore errors if you set this to false and the destination
exists. Use the
errorOnExist
option to change this behavior.
Default:
true
mode

modifiers for copy operation.
Default:
See
mode
flag of
fs.copyFile()
preserveTimestamps

When
true
timestamps from
src
will
be preserved.
Default:
false
recursive

copy directories recursively
Default:
false
verbatimSymlinks

When
true
, path resolution for symlinks will
be skipped.
Default:
false
callback

err

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/
fs.createReadStream(path[, options])
Added in: v0.1.31
History
Version
Changes
v16.10.0
The
fs
option does not need
open
method if an
fd
was provided.
v16.10.0
The
fs
option does not need
close
method if
autoClose
is
false
v15.5.0
Add support for
AbortSignal
v15.4.0
The
fd
option accepts FileHandle arguments.
v14.0.0
Change
emitClose
default to
true
v13.6.0, v12.17.0
The
fs
options allow overriding the used
fs
implementation.
v12.10.0
Enable
emitClose
option.
v11.0.0
Impose new restrictions on
start
and
end
, throwing more appropriate errors in cases when we cannot reasonably handle the input values.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The passed
options
object will never be modified.
v2.3.0
The passed
options
object can be a string now.
path



options


flags

See
support of file system
flags
Default:
'r'
encoding

Default:
null
fd


Default:
null
mode

Default:
0o666
autoClose

Default:
true
emitClose

Default:
true
start

end

Default:
Infinity
highWaterMark

Default:
64 * 1024
fs


Default:
null
signal


Default:
null
Returns:

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
fd
is specified and
start
is
omitted or
undefined
fs.createReadStream()
reads sequentially from the
current file position. The
encoding
can be any one of those accepted by

If
fd
is specified,
ReadStream
will ignore the
path
argument and will use
the specified file descriptor. This means that no
'open'
event will be
emitted.
fd
should be blocking; non-blocking
fd
s should be passed to

If
fd
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.
By providing the
fs
option, it is possible to override the corresponding
fs
implementations for
open
read
, and
close
. When providing the
fs
option,
an override for
read
is required. If no
fd
is provided, an override for
open
is also required. If
autoClose
is
true
, an override for
close
is
also required.
import
createReadStream
from
'node:fs'
// Create a stream from some character device.
const
stream
createReadStream
'/dev/input/event0'
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
},
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.
mode
sets the file mode (permission and sticky bits), but only if the
file was created.
An example to read the last 10 bytes of a file which is 100 bytes long:
import
createReadStream
from
'node:fs'
createReadStream
'sample.txt'
start
90
end
99
If
options
is a string, then it specifies the encoding.
fs.createWriteStream(path[, options])
Added in: v0.1.31
History
Version
Changes
v21.0.0, v20.10.0
The
flush
option is now supported.
v16.10.0
The
fs
option does not need
open
method if an
fd
was provided.
v16.10.0
The
fs
option does not need
close
method if
autoClose
is
false
v15.5.0
Add support for
AbortSignal
v15.4.0
The
fd
option accepts FileHandle arguments.
v14.0.0
Change
emitClose
default to
true
v13.6.0, v12.17.0
The
fs
options allow overriding the used
fs
implementation.
v12.10.0
Enable
emitClose
option.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The passed
options
object will never be modified.
v5.5.0
The
autoClose
option is supported now.
v2.3.0
The passed
options
object can be a string now.
path



options


flags

See
support of file system
flags
Default:
'w'
encoding

Default:
'utf8'
fd


Default:
null
mode

Default:
0o666
autoClose

Default:
true
emitClose

Default:
true
start

fs


Default:
null
signal


Default:
null
highWaterMark

Default:
16384
flush

If
true
, the underlying file descriptor is flushed
prior to closing it.
Default:
false
Returns:

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
option to be set to
r+
rather than the
default
. The
encoding
can be any one of those accepted by

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.
By providing the
fs
option it is possible to override the corresponding
fs
implementations for
open
write
writev
, and
close
. Overriding
write()
without
writev()
can reduce performance as some optimizations (
_writev()
will be disabled. When providing the
fs
option, overrides for at least one of
write
and
writev
are required. If no
fd
option is supplied, an override
for
open
is also required. If
autoClose
is
true
, an override for
close
is also required.
Like

, if
fd
is specified,

will ignore the
path
argument and will use the specified file descriptor. This means that no
'open'
event will be emitted.
fd
should be blocking; non-blocking
fd
should be passed to

If
options
is a string, then it specifies the encoding.
fs.exists(path, callback)
Added in: v0.0.2
Deprecated in: v1.0.0
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
Stability: 0 - Deprecated: Use
fs.stat()
or
fs.access()
instead.
path



callback

exists

Test whether or not the element at the given
path
exists by checking with the file system.
Then call the
callback
argument with either true or false:
import
exists
from
'node:fs'
exists
'/etc/passwd'
=>
console
log
(e
'it exists'
'no passwd!'
The parameters for this callback are not consistent with other Node.js
callbacks.
Normally, the first parameter to a Node.js callback is an
err
parameter, optionally followed by other parameters. The
fs.exists()
callback
has only one boolean parameter. This is one reason
fs.access()
is recommended
instead of
fs.exists()
If
path
is a symbolic link, it is followed. Thus, if
path
exists but points
to a non-existent element, the callback will receive the value
false
Using
fs.exists()
to check for the existence of a file before calling
fs.open()
fs.readFile()
, or
fs.writeFile()
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 does not exist.
write (NOT RECOMMENDED)
import
exists
open
close
from
'node:fs'
exists
'myfile'
=>
if
(e)
console
error
'myfile already exists'
else
open
'myfile'
'wx'
err
fd
=>
if
(err)
throw
err
try
writeMyData
(fd)
finally
close
(fd
err
=>
if
(err)
throw
err
write (RECOMMENDED)
import
open
close
from
'node:fs'
open
'myfile'
'wx'
err
fd
=>
if
(err)
if
(err
code
===
'EEXIST'
console
error
'myfile already exists'
return
throw
err
try
writeMyData
(fd)
finally
close
(fd
err
=>
if
(err)
throw
err
read (NOT RECOMMENDED)
import
open
close
exists
from
'node:fs'
exists
'myfile'
=>
if
(e)
open
'myfile'
'r'
err
fd
=>
if
(err)
throw
err
try
readMyData
(fd)
finally
close
(fd
err
=>
if
(err)
throw
err
else
console
error
'myfile does not exist'
read (RECOMMENDED)
import
open
close
from
'node:fs'
open
'myfile'
'r'
err
fd
=>
if
(err)
if
(err
code
===
'ENOENT'
console
error
'myfile does not exist'
return
throw
err
try
readMyData
(fd)
finally
close
(fd
err
=>
if
(err)
throw
err
The "not recommended" examples above check for existence and then use the
file; the "recommended" examples are better because they use the file directly
and handle the error, if any.
In general, check for the existence of a file only if the file won't be
used directly, for example when its existence is a signal from another
process.
fs.fchmod(fd, mode, callback)
Added in: v0.4.7
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
fd

mode


callback

err

Sets the permissions on the file. No arguments other than a possible exception
are given to the completion callback.
See the POSIX
fchmod(2)
documentation for more detail.
fs.fchown(fd, uid, gid, callback)
Added in: v0.4.7
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
fd

uid

gid

callback

err

Sets the owner of the file. No arguments other than a possible exception are
given to the completion callback.
See the POSIX
fchown(2)
documentation for more detail.
fs.fdatasync(fd, callback)
Added in: v0.1.96
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
fd

callback

err

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. No arguments other than a possible
exception are given to the completion callback.
fs.fstat(fd[, options], callback)
Added in: v0.1.95
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.5.0
Accepts an additional
options
object to specify whether the numeric values returned should be bigint.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
fd

options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
callback

err

stats

Invokes the callback with the

for the file descriptor.
See the POSIX
fstat(2)
documentation for more detail.
fs.fsync(fd, callback)
Added in: v0.1.96
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
fd

callback

err

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. No arguments other
than a possible exception are given to the completion callback.
fs.ftruncate(fd[, len], callback)
Added in: v0.8.6
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
fd

len

Default:
callback

err

Truncates the file descriptor. No arguments other than a possible exception are
given to the completion callback.
See the POSIX
ftruncate(2)
documentation for more detail.
If the file referred to by the file descriptor was larger than
len
bytes, only
the first
len
bytes will be retained in the file.
For example, the following program retains only the first four bytes of the
file:
import
open
close
ftruncate
from
'node:fs'
function
closeFd
fd
close
(fd
err
=>
if
(err)
throw
err
open
'temp.txt'
'r+'
err
fd
=>
if
(err)
throw
err
try
ftruncate
(fd
err
=>
closeFd
(fd)
if
(err)
throw
err
catch
(err)
closeFd
(fd)
if
(err)
throw
err
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
will be used.
fs.futimes(fd, atime, mtime, callback)
Added in: v0.4.2
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
v4.1.0
Numeric strings,
NaN
, and
Infinity
are now allowed time specifiers.
fd

atime



mtime



callback

err

Change the file system timestamps of the object referenced by the supplied file
descriptor. See
fs.utimes()
fs.glob(pattern[, options], callback)
Added in: v22.0.0
History
Version
Changes
v24.1.0, v22.17.0
Add support for
URL
instances for
cwd
option.
v24.0.0, v22.17.0
Marking the API stable.
v23.7.0, v22.14.0
Add support for
exclude
option to accept glob patterns.
v22.2.0
Add support for
withFileTypes
as an option.
pattern


options

cwd


current working directory.
Default:
process.cwd()
exclude


Function to filter out files/directories or a
list of glob patterns to be excluded. If a function is provided, return
true
to exclude the item,
false
to include it.
Default:
undefined
withFileTypes

true
if the glob should return paths as Dirents,
false
otherwise.
Default:
false
callback

err

Retrieves the files matching the specified pattern.
import
glob
from
'node:fs'
glob
'**/*.js'
err
matches
=>
if
(err)
throw
err
console
log
(matches)
const
glob
require
'node:fs'
glob
'**/*.js'
err
matches
=>
if
(err)
throw
err
console
log
(matches)
fs.lchmod(path, mode, callback)
Deprecated in: v0.4.7
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v16.0.0
The error returned may be an
AggregateError
if more than one error is returned.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
Stability: 0 - Deprecated
path



mode

callback

err


Changes the permissions on a symbolic link. No arguments other than a possible
exception are given to the completion callback.
This method is only implemented on macOS.
See the POSIX
lchmod(2)
documentation for more detail.
fs.lchown(path, uid, gid, callback)
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.6.0
This API is no longer deprecated.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
v0.4.7
Documentation-only deprecation.
path



uid

gid

callback

err

Set the owner of the symbolic link. No arguments other than a possible
exception are given to the completion callback.
See the POSIX
lchown(2)
documentation for more detail.
fs.lutimes(path, atime, mtime, callback)
Added in: v14.5.0, v12.19.0
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
path



atime



mtime



callback

err

Changes the access and modification times of a file in the same way as
fs.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.
No arguments other than a possible exception are given to the completion
callback.
fs.link(existingPath, newPath, callback)
Added in: v0.1.31
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
existingPath
and
newPath
parameters can be WHATWG
URL
objects using
file:
protocol. Support is currently still
experimental
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
existingPath



newPath



callback

err

Creates a new link from the
existingPath
to the
newPath
. See the POSIX
link(2)
documentation for more detail. No arguments other than a possible
exception are given to the completion callback.
fs.lstat(path[, options], callback)
Added in: v0.1.30
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.5.0
Accepts an additional
options
object to specify whether the numeric values returned should be bigint.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
path



options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
callback

err

stats

Retrieves the

for the symbolic link referred to by the path.
The callback gets two arguments
(err, stats)
where
stats
is a

object.
lstat()
is identical to
stat()
, except that if
path
is a symbolic
link, then the link itself is stat-ed, not the file that it refers to.
See the POSIX
lstat(2)
documentation for more details.
fs.mkdir(path[, options], callback)
Added in: v0.1.8
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v13.11.0, v12.17.0
In
recursive
mode, the callback now receives the first created path as an argument.
v10.12.0
The second argument can now be an
options
object with
recursive
and
mode
properties.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
path



options


recursive

Default:
false
mode


Not supported on Windows. See
File modes
for more details.
Default:
0o777
callback

err

path


Present only if a directory is created with
recursive
set to
true
Asynchronously creates a directory.
The callback is given a possible exception and, if
recursive
is
true
, the
first directory path created,
(err[, path])
path
can still be
undefined
when
recursive
is
true
, if no directory was
created (for instance, if it was previously created).
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
fs.mkdir()
when
path
is a directory that exists results in an error only
when
recursive
is false. If
recursive
is false and the directory exists,
an
EEXIST
error occurs.
import
mkdir
from
'node:fs'
// Create ./tmp/a/apple, regardless of whether ./tmp and ./tmp/a exist.
mkdir
'./tmp/a/apple'
recursive
true
},
err
=>
if
(err)
throw
err
On Windows, using
fs.mkdir()
on the root directory even with recursion will
result in an error:
import
mkdir
from
'node:fs'
mkdir
'/'
recursive
true
},
err
=>
// => [Error: EPERM: operation not permitted, mkdir 'C:\']
See the POSIX
mkdir(2)
documentation for more details.
fs.mkdtemp(prefix[, options], callback)
Added in: v5.10.0
History
Version
Changes
v20.6.0, v18.19.0
The
prefix
parameter now accepts buffers and URL.
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v16.5.0, v14.18.0
The
prefix
parameter now accepts an empty string.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
v6.2.1
The
callback
parameter is optional now.
prefix



options


encoding

Default:
'utf8'
callback

err

directory

Creates a unique temporary directory.
Generates six random characters to be appended behind a required
prefix
to create a unique temporary directory. Due to platform
inconsistencies, avoid trailing
characters in
prefix
. Some platforms,
notably the BSDs, can return more than six random characters, and replace
trailing
characters in
prefix
with random characters.
The created directory path is passed as a string to the callback's second
parameter.
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'
import
join
from
'node:path'
import
tmpdir
from
'node:os'
mkdtemp
join
tmpdir
()
'foo-'
err
directory
=>
if
(err)
throw
err
console
log
(directory)
// Prints: /tmp/foo-itXde2 or C:\Users\...\AppData\Local\Temp\foo-itXde2
The
fs.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('node:path').sep
).
import
tmpdir
from
'node:os'
import
mkdtemp
from
'node:fs'
// The parent directory for the new temporary directory
const
tmpDir
tmpdir
()
// This method is *INCORRECT*:
mkdtemp
(tmpDir
err
directory
=>
if
(err)
throw
err
console
log
(directory)
// Will print something similar to `/tmpabc123`.
// A new temporary directory is created at the file system root
// rather than *within* the /tmp directory.
// This method is *CORRECT*:
import
sep
from
'node:path'
mkdtemp
${
tmpDir
}${
sep
err
directory
=>
if
(err)
throw
err
console
log
(directory)
// Will print something similar to `/tmp/abc123`.
// A new temporary directory is created within
// the /tmp directory.
fs.open(path[, flags[, mode]], callback)
Added in: v0.0.2
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v11.1.0
The
flags
argument is now optional and defaults to
'r'
v9.9.0
The
as
and
as+
flags are supported now.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



flags


See
support of file system
flags
Default:
'r'
mode


Default:
0o666
(readable and writable)
callback

err

fd

Asynchronous file open. See the POSIX
open(2)
documentation for more details.
mode
sets the file mode (permission and sticky bits), but only if the file was
created. On Windows, only the write permission can be manipulated; see
fs.chmod()
The callback gets two arguments
(err, fd)
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
Functions based on
fs.open()
exhibit this behavior as well:
fs.writeFile()
fs.readFile()
, etc.
fs.openAsBlob(path[, options])
Added in: v19.8.0
History
Version
Changes
v24.0.0, v22.17.0
Marking the API stable.
path



options

type

An optional mime type for the blob.
Returns:

Fulfills with a

upon success.
Returns a

whose data is backed by the given file.
The file must not be modified after the

is created. Any modifications
will cause reading the

data to fail with a
DOMException
error.
Synchronous stat operations on the file when the
Blob
is created, and before
each read in order to detect whether the file data has been modified on disk.
import
openAsBlob
from
'node:fs'
const
blob
await
openAsBlob
'the.file.txt'
const
ab
await
blob
arrayBuffer
()
blob
stream
()
const
openAsBlob
require
'node:fs'
async
()
=>
const
blob
await
openAsBlob
'the.file.txt'
const
ab
await
blob
arrayBuffer
()
blob
stream
()
)()
fs.opendir(path[, options], callback)
Added in: v12.12.0
History
Version
Changes
v20.1.0, v18.17.0
Added
recursive
option.
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v13.1.0, v12.16.0
The
bufferSize
option was introduced.
path



options

encoding


Default:
'utf8'
bufferSize

Number of directory entries that are buffered
internally when reading from the directory. Higher values lead to better
performance but higher memory usage.
Default:
32
recursive

Default:
false
callback

err

dir

Asynchronously open a directory. See the POSIX
opendir(3)
documentation for
more details.
Creates an

, 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.
fs.read(fd, buffer, offset, length, position, callback)
Added in: v0.0.2
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.10.0
The
buffer
parameter can now be any
TypedArray
, or a
DataView
v7.4.0
The
buffer
parameter can now be a
Uint8Array
v6.0.0
The
length
parameter can now be
fd

buffer



The buffer that the data will be
written to.
offset

The position in
buffer
to write the data to.
length

The number of bytes to read.
position



Specifies where to begin reading from in the
file. If
position
is
null
or
-1
, data will be read from the current
file position, and the file position will be updated. If
position
is
a non-negative integer, the file position will be unchanged.
callback

err

bytesRead

buffer

Read data from the file specified by
fd
The callback is given the three arguments,
(err, bytesRead, buffer)
If the file is not modified concurrently, the end-of-file is reached when the
number of bytes read is zero.
If this method is invoked as its
util.promisify()
ed version, it returns
a promise for an
Object
with
bytesRead
and
buffer
properties.
The
fs.read()
method reads data from the file specified
by the file descriptor (
fd
).
The
length
argument indicates the maximum number
of bytes that Node.js
will attempt to read from the kernel.
However, the actual number of bytes read (
bytesRead
) can be lower
than the specified
length
for various reasons.
For example:
If the file is shorter than the specified
length
bytesRead
will be set to the actual number of bytes read.
If the file encounters EOF (End of File) before the buffer could
be filled, Node.js will read all available bytes until EOF is encountered,
and the
bytesRead
parameter in the callback will indicate
the actual number of bytes read, which may be less than the specified
length
If the file is on a slow network
filesystem
or encounters any other issue during reading,
bytesRead
can be lower than the specified
length
Therefore, when using
fs.read()
, it's important to
check the
bytesRead
value to
determine how many bytes were actually read from the file.
Depending on your application
logic, you may need to handle cases where
bytesRead
is lower than the specified
length
such as by wrapping the read call in a loop if you require
a minimum amount of bytes.
This behavior is similar to the POSIX
preadv2
function.
fs.read(fd[, options], callback)
Added in: v13.11.0, v12.17.0
History
Version
Changes
v13.11.0, v12.17.0
Options object can be passed in to make buffer, offset, length, and position optional.
fd

options

buffer



Default:
Buffer.alloc(16384)
offset

Default:
length

Default:
buffer.byteLength - offset
position



Default:
null
callback

err

bytesRead

buffer

Similar to the
fs.read()
function, this version takes an optional
options
object. If no
options
object is specified, it will default with the
above values.
fs.read(fd, buffer[, options], callback)
Added in: v18.2.0, v16.17.0
fd

buffer



The buffer that the data will be
written to.
options

offset

Default:
length

Default:
buffer.byteLength - offset
position


Default:
null
callback

err

bytesRead

buffer

Similar to the
fs.read()
function, this version takes an optional
options
object. If no
options
object is specified, it will default with the
above values.
fs.readdir(path[, options], callback)
Added in: v0.1.8
History
Version
Changes
v20.1.0, v18.17.0
Added
recursive
option.
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.10.0
New option
withFileTypes
was added.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
v6.0.0
The
options
parameter was added.
path



options


encoding

Default:
'utf8'
withFileTypes

Default:
false
recursive

If
true
, reads the contents of a directory
recursively. In recursive mode, it will list all files, sub files and
directories.
Default:
false
callback

err

files



Reads the contents of a directory. The callback gets two arguments
(err, files)
where
files
is an array of the names of the files in the directory excluding
'.'
and
'..'
See the POSIX
readdir(3)
documentation for more details.
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 passed to the callback. If the
encoding
is set to
'buffer'
the filenames returned will be passed as

objects.
If
options.withFileTypes
is set to
true
, the
files
array will contain

objects.
fs.readFile(path[, options], callback)
Added in: v0.1.29
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v16.0.0
The error returned may be an
AggregateError
if more than one error is returned.
v15.2.0, v14.17.0
The options argument may include an AbortSignal to abort an ongoing readFile request.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
v5.1.0
The
callback
will always be called with
null
as the
error
parameter in case of success.
v5.0.0
The
path
parameter can be a file descriptor now.
path




filename or file descriptor
options


encoding


Default:
null
flag

See
support of file system
flags
Default:
'r'
signal

allows aborting an in-progress readFile
callback

err


data


Asynchronously reads the entire contents of a file.
import
readFile
from
'node:fs'
readFile
'/etc/passwd'
err
data
=>
if
(err)
throw
err
console
log
(data)
The callback is passed two arguments
(err, data)
, where
data
is the
contents of the file.
If no encoding is specified, then the raw buffer is returned.
If
options
is a string, then it specifies the encoding:
import
readFile
from
'node:fs'
readFile
'/etc/passwd'
'utf8'
callback)
When the path is a directory, the behavior of
fs.readFile()
and
fs.readFileSync()
is platform-specific. On macOS, Linux, and Windows, an
error will be returned. On FreeBSD, a representation of the directory's contents
will be returned.
import
readFile
from
'node:fs'
// macOS, Linux, and Windows
readFile
''
err
data
=>
// => [Error: EISDIR: illegal operation on a directory, read ]
// FreeBSD
readFile
''
err
data
=>
// => null,
It is possible to abort an ongoing request using an
AbortSignal
. If a
request is aborted the callback is called with an
AbortError
import
readFile
from
'node:fs'
const
controller
new
AbortController
()
const
signal
controller
signal
readFile
(fileInfo[
name
signal
},
err
buf
=>
// ...
// When you want to abort the request
controller
abort
()
The
fs.readFile()
function buffers the entire file. To minimize memory costs,
when possible prefer streaming via
fs.createReadStream()
Aborting an ongoing request does not abort individual operating
system requests but rather the internal buffering
fs.readFile
performs.
File descriptors
Any specified file descriptor has to support reading.
If a file descriptor is specified as the
path
, it will not be closed
automatically.
The reading will begin at the current position. For example, if the file
already had
'Hello World'
and six bytes are read with the file descriptor,
the call to
fs.readFile()
with the same file descriptor, would give
'World'
, rather than
'Hello World'
Performance Considerations
The
fs.readFile()
method asynchronously reads the contents of a file into
memory one chunk at a time, allowing the event loop to turn between each chunk.
This allows the read operation to have less impact on other activity that may
be using the underlying libuv thread pool but means that it will take longer
to read a complete file into memory.
The additional read overhead can vary broadly on different systems and depends
on the type of file being read. If the file type is not a regular file (a pipe
for instance) and Node.js is unable to determine an actual file size, each read
operation will load on 64 KiB of data. For regular files, each read will process
512 KiB of data.
For applications that require as-fast-as-possible reading of file contents, it
is better to use
fs.read()
directly and for application code to manage
reading the full contents of the file itself.
The Node.js GitHub issue
#25741
provides more information and a detailed
analysis on the performance of
fs.readFile()
for multiple file sizes in
different Node.js versions.
fs.readlink(path[, options], callback)
Added in: v0.1.31
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
path



options


encoding

Default:
'utf8'
callback

err

linkString


Reads the contents of the symbolic link referred to by
path
. The callback gets
two arguments
(err, linkString)
See the POSIX
readlink(2)
documentation for more details.
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 passed to the callback. If the
encoding
is set to
'buffer'
the link path returned will be passed as a

object.
fs.readv(fd, buffers[, position], callback)
Added in: v13.13.0, v12.17.0
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
fd

buffers

position


Default:
null
callback

err

bytesRead

buffers

Read from a file specified by
fd
and write to an array of
ArrayBufferView
using
readv()
position
is the offset from the beginning of the file from where data
should be read. If
typeof position !== 'number'
, the data will be read
from the current position.
The callback will be given three arguments:
err
bytesRead
, and
buffers
bytesRead
is how many bytes were read from the file.
If this method is invoked as its
util.promisify()
ed version, it returns
a promise for an
Object
with
bytesRead
and
buffers
properties.
fs.realpath(path[, options], callback)
Added in: v0.1.31
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v8.0.0
Pipe/Socket resolve support was added.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
v6.4.0
Calling
realpath
now works again for various edge cases on Windows.
v6.0.0
The
cache
parameter was removed.
path



options


encoding

Default:
'utf8'
callback

err

resolvedPath


Asynchronously computes the canonical pathname by resolving
..
, and
symbolic links.
A canonical pathname is not necessarily unique. Hard links and bind mounts can
expose a file system entity through many pathnames.
This function behaves like
realpath(3)
, with some exceptions:
No case conversion is performed on case-insensitive file systems.
The maximum number of symbolic links is platform-independent and generally
(much) higher than what the native
realpath(3)
implementation supports.
The
callback
gets two arguments
(err, resolvedPath)
. May use
process.cwd
to resolve relative paths.
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 passed to the callback. If the
encoding
is set to
'buffer'
the path returned will be passed as a

object.
If
path
resolves to a socket or a pipe, the function will return a system
dependent name for that object.
A path that does not exist results in an ENOENT error.
error.path
is the absolute file path.
fs.realpath.native(path[, options], callback)
Added in: v9.2.0
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
path



options


encoding

Default:
'utf8'
callback

err

resolvedPath


Asynchronous
realpath(3)
The
callback
gets two arguments
(err, resolvedPath)
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 passed to the callback. If the
encoding
is set to
'buffer'
the path returned will be passed as a

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.
fs.rename(oldPath, newPath, callback)
Added in: v0.0.2
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
oldPath
and
newPath
parameters can be WHATWG
URL
objects using
file:
protocol. Support is currently still
experimental
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
oldPath



newPath



callback

err

Asynchronously rename file at
oldPath
to the pathname provided
as
newPath
. In the case that
newPath
already exists, it will
be overwritten. If there is a directory at
newPath
, an error will
be raised instead. No arguments other than a possible exception are
given to the completion callback.
See also:
rename(2)
import
rename
from
'node:fs'
rename
'oldFile.txt'
'newFile.txt'
err
=>
if
(err)
throw
err
console
log
'Rename complete!'
fs.rmdir(path[, options], callback)
Added in: v0.0.2
History
Version
Changes
v25.0.0
Remove
recursive
option.
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v16.0.0
Using
fs.rmdir(path, { recursive: true })
on a
path
that is a file is no longer permitted and results in an
ENOENT
error on Windows and an
ENOTDIR
error on POSIX.
v16.0.0
Using
fs.rmdir(path, { recursive: true })
on a
path
that does not exist is no longer permitted and results in a
ENOENT
error.
v16.0.0
The
recursive
option is deprecated, using it triggers a deprecation warning.
v14.14.0
The
recursive
option is deprecated, use
fs.rm
instead.
v13.3.0, v12.16.0
The
maxBusyTries
option is renamed to
maxRetries
, and its default is 0. The
emfileWait
option has been removed, and
EMFILE
errors use the same retry logic as other errors. The
retryDelay
option is now supported.
ENFILE
errors are now retried.
v12.10.0
The
recursive
maxBusyTries
, and
emfileWait
options are now supported.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameters can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
path



options

There are currently no options exposed. There used to
be options for
recursive
maxBusyTries
, and
emfileWait
but they were
deprecated and removed. The
options
argument is still accepted for
backwards compatibility but it is not used.
callback

err

Asynchronous
rmdir(2)
. No arguments other than a possible exception are given
to the completion callback.
Using
fs.rmdir()
on a file (not a directory) results in an
ENOENT
error on
Windows and an
ENOTDIR
error on POSIX.
To get a behavior similar to the
rm -rf
Unix command, use
fs.rm()
with options
{ recursive: true, force: true }
fs.rm(path[, options], callback)
Added in: v14.14.0
History
Version
Changes
v17.3.0, v16.14.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



options

force

When
true
, exceptions will be ignored if
path
does
not exist.
Default:
false
maxRetries

If an
EBUSY
EMFILE
ENFILE
ENOTEMPTY
, or
EPERM
error is encountered, Node.js will retry the operation with a linear
backoff wait of
retryDelay
milliseconds longer on each try. This option
represents the number of retries. This option is ignored if the
recursive
option is not
true
Default:
recursive

If
true
, perform a recursive removal. In
recursive mode operations are retried on failure.
Default:
false
retryDelay

The amount of time in milliseconds to wait between
retries. This option is ignored if the
recursive
option is not
true
Default:
100
callback

err

Asynchronously removes files and directories (modeled on the standard POSIX
rm
utility). No arguments other than a possible exception are given to the
completion callback.
fs.stat(path[, options], callback)
Added in: v0.0.2
History
Version
Changes
v25.7.0
Accepts a
throwIfNoEntry
option to specify whether an exception should be thrown if the entry does not exist.
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.5.0
Accepts an additional
options
object to specify whether the numeric values returned should be bigint.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
path



options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
throwIfNoEntry

Whether an exception will be thrown
if no file system entry exists, rather than returning
undefined
Default:
true
callback

err

stats

Asynchronous
stat(2)
. The callback gets two arguments
(err, stats)
where
stats
is an

object.
In case of an error, the
err.code
will be one of
Common System Errors
fs.stat()
follows symbolic links. Use
fs.lstat()
to look at the
links themselves.
Using
fs.stat()
to check for the existence of a file before calling
fs.open()
fs.readFile()
, or
fs.writeFile()
is not recommended.
Instead, user code should open/read/write the file directly and handle the
error raised if the file is not available.
To check if a file exists without manipulating it afterwards,
fs.access()
is recommended.
For example, given the following directory structure:
- txtDir
-- file.txt
- app.js
The next program will check for the stats of the given paths:
import
stat
from
'node:fs'
const
pathsToCheck
'./txtDir'
'./txtDir/file.txt'
for
let
pathsToCheck
length
++
stat
(pathsToCheck[i]
err
stats
=>
console
log
(stats
isDirectory
())
console
log
(stats)
The resulting output will resemble:
true
Stats {
dev: 16777220,
mode: 16877,
nlink: 3,
uid: 501,
gid: 20,
rdev: 0,
blksize: 4096,
ino: 14214262,
size: 96,
blocks: 0,
atimeMs: 1561174653071.963,
mtimeMs: 1561174614583.3518,
ctimeMs: 1561174626623.5366,
birthtimeMs: 1561174126937.2893,
atime: 2019-06-22T03:37:33.072Z,
mtime: 2019-06-22T03:36:54.583Z,
ctime: 2019-06-22T03:37:06.624Z,
birthtime: 2019-06-22T03:28:46.937Z
false
Stats {
dev: 16777220,
mode: 33188,
nlink: 1,
uid: 501,
gid: 20,
rdev: 0,
blksize: 4096,
ino: 14214074,
size: 8,
blocks: 8,
atimeMs: 1561174616618.8555,
mtimeMs: 1561174614584,
ctimeMs: 1561174614583.8145,
birthtimeMs: 1561174007710.7478,
atime: 2019-06-22T03:36:56.619Z,
mtime: 2019-06-22T03:36:54.584Z,
ctime: 2019-06-22T03:36:54.584Z,
birthtime: 2019-06-22T03:26:47.711Z
fs.statfs(path[, options], callback)
Added in: v19.6.0, v18.15.0
path



options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
callback

err

stats

Asynchronous
statfs(2)
. Returns information about the mounted file system which
contains
path
. The callback gets two arguments
(err, stats)
where
stats
is an

object.
In case of an error, the
err.code
will be one of
Common System Errors
fs.symlink(target, path[, type], callback)
Added in: v0.1.31
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v12.0.0
If the
type
argument is left undefined, Node will autodetect
target
type and automatically select
dir
or
file
v7.6.0
The
target
and
path
parameters can be WHATWG
URL
objects using
file:
protocol. Support is currently still
experimental
target



path



type


Default:
null
callback

err

Creates the link called
path
pointing to
target
. No arguments other than a
possible exception are given to the completion callback.
See the POSIX
symlink(2)
documentation for more details.
The
type
argument is only available on Windows and ignored on other platforms.
It can be set to
'dir'
'file'
, or
'junction'
. If the
type
argument is
null
, 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.
Relative targets are relative to the link's parent directory.
import
symlink
from
'node:fs'
symlink
'./mew'
'./mewtwo'
callback)
The above example creates a symbolic link
mewtwo
which points to
mew
in the
same directory:
tree
├──
mew
└──
mewtwo
./mew
fs.truncate(path[, len], callback)
Added in: v0.8.6
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v16.0.0
The error returned may be an
AggregateError
if more than one error is returned.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
path



len

Default:
callback

err


Truncates the file. No arguments other than a possible exception are
given to the completion callback. A file descriptor can also be passed as the
first argument. In this case,
fs.ftruncate()
is called.
import
truncate
from
'node:fs'
// Assuming that 'path/file.txt' is a regular file.
truncate
'path/file.txt'
err
=>
if
(err)
throw
err
console
log
'path/file.txt was truncated'
const
truncate
require
'node:fs'
// Assuming that 'path/file.txt' is a regular file.
truncate
'path/file.txt'
err
=>
if
(err)
throw
err
console
log
'path/file.txt was truncated'
Passing a file descriptor is deprecated and may result in an error being thrown
in the future.
See the POSIX
truncate(2)
documentation for more details.
fs.unlink(path, callback)
Added in: v0.0.2
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
path



callback

err

Asynchronously removes a file or symbolic link. No arguments other than a
possible exception are given to the completion callback.
import
unlink
from
'node:fs'
// Assuming that 'path/file.txt' is a regular file.
unlink
'path/file.txt'
err
=>
if
(err)
throw
err
console
log
'path/file.txt was deleted'
fs.unlink()
will not work on a directory, empty or otherwise. To remove a
directory, use
fs.rmdir()
See the POSIX
unlink(2)
documentation for more details.
fs.unwatchFile(filename[, listener])
Added in: v0.1.31
filename



listener

Optional, a listener previously attached using
fs.watchFile()
Stop watching for changes on
filename
. If
listener
is specified, only that
particular listener is removed. Otherwise,
all
listeners are removed,
effectively stopping watching of
filename
Calling
fs.unwatchFile()
with a filename that is not being watched is a
no-op, not an error.
Using
fs.watch()
is more efficient than
fs.watchFile()
and
fs.unwatchFile()
fs.watch()
should be used instead of
fs.watchFile()
and
fs.unwatchFile()
when possible.
fs.utimes(path, atime, mtime, callback)
Added in: v0.4.2
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v8.0.0
NaN
Infinity
, and
-Infinity
are no longer valid time specifiers.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
v4.1.0
Numeric strings,
NaN
, and
Infinity
are now allowed time specifiers.
path



atime



mtime



callback

err

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 in seconds,
Date
s, 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.
fs.watch(filename[, options][, listener])
Added in: v0.5.10
History
Version
Changes
v19.1.0
Added recursive support for Linux, AIX and IBMi.
v15.9.0, v14.17.0
Added support for closing the watcher with an AbortSignal.
v7.6.0
The
filename
parameter can be a WHATWG
URL
object using
file:
protocol.
v7.0.0
The passed
options
object will never be modified.
filename



options


persistent

Indicates whether the process should continue to run
as long as files are being watched.
Default:
true
recursive

Indicates whether all subdirectories should be
watched, or only the current directory. This applies when a directory is
specified, and only on supported platforms (See
caveats
).
Default:
false
encoding

Specifies the character encoding to be used for the
filename passed to the listener.
Default:
'utf8'
signal

allows closing the watcher with an AbortSignal.
ignore




Pattern(s) to ignore. Strings are
glob patterns (using
minimatch
), RegExp patterns are tested against
the filename, and functions receive the filename and return
true
to
ignore.
Default:
undefined
listener


Default:
undefined
eventType

filename



Returns:

Watch for changes on
filename
, where
filename
is either a file or a
directory.
The second argument is optional. If
options
is provided as a string, it
specifies the
encoding
. Otherwise
options
should be passed as an object.
The listener callback gets two arguments
(eventType, filename)
eventType
is either
'rename'
or
'change'
, and
filename
is the name of the file
which triggered the event.
On most platforms,
'rename'
is emitted whenever a filename appears or
disappears in the directory.
The listener callback is attached to the
'change'
event fired by

, but it is not the same thing as the
'change'
value of
eventType
If a
signal
is passed, aborting the corresponding AbortController will close
the returned

Caveats
The
fs.watch
API is not 100% consistent across platforms, and is
unavailable in some situations.
On Windows, no events will be emitted if the watched directory is moved or
renamed. An
EPERM
error is reported when the watched directory is deleted.
The
fs.watch
API does not provide any protection with respect
to malicious actions on the file system. For example, on Windows it is
implemented by monitoring changes in a directory versus specific files. This
allows substitution of a file and fs reporting changes on the new file
with the same filename.
Availability
This feature depends on the underlying operating system providing a way
to be notified of file system changes.
On Linux systems, this uses
inotify(7)
On BSD systems, this uses
kqueue(2)
On macOS, this uses
kqueue(2)
for files and
FSEvents
for
directories.
On SunOS systems (including Solaris and SmartOS), this uses
event ports
On Windows systems, this feature depends on
ReadDirectoryChangesW
On AIX systems, this feature depends on
AHAFS
, which must be enabled.
On IBM i systems, this feature is not supported.
If the underlying functionality is not available for some reason, then
fs.watch()
will not be able to function and may throw an exception.
For example, watching files or directories can be unreliable, and in some
cases impossible, on network file systems (NFS, SMB, etc) or host file systems
when using virtualization software such as Vagrant or Docker.
It is still possible to use
fs.watchFile()
, which uses stat polling, but
this method is slower and less reliable.
Inodes
On Linux and macOS systems,
fs.watch()
resolves the path to an
inode
and
watches the inode. If the watched path is deleted and recreated, it is assigned
a new inode. The watch will emit an event for the delete but will continue
watching the
original
inode. Events for the new inode will not be emitted.
This is expected behavior.
AIX files retain the same inode for the lifetime of a file. Saving and closing a
watched file on AIX will result in two notifications (one for adding new
content, and one for truncation).
Filename argument
Providing
filename
argument in the callback is only supported on Linux,
macOS, Windows, and AIX. Even on supported platforms,
filename
is not always
guaranteed to be provided. Therefore, don't assume that
filename
argument is
always provided in the callback, and have some fallback logic if it is
null
import
watch
from
'node:fs'
watch
'somedir'
eventType
filename
=>
console
log
`event type is:
${
eventType
if
(filename)
console
log
`filename provided:
${
filename
else
console
log
'filename not provided'
fs.watchFile(filename[, options], listener)
Added in: v0.1.31
History
Version
Changes
v10.5.0
The
bigint
option is now supported.
v7.6.0
The
filename
parameter can be a WHATWG
URL
object using
file:
protocol.
filename



options

bigint

Default:
false
persistent

Default:
true
interval

Default:
5007
listener

current

previous

Returns:

Watch for changes on
filename
. The callback
listener
will be called each
time the file is accessed.
The
options
argument may be omitted. If provided, it should be an object. The
options
object may contain a boolean named
persistent
that indicates
whether the process should continue to run as long as files are being watched.
The
options
object may specify an
interval
property indicating how often the
target should be polled in milliseconds.
The
listener
gets two arguments the current stat object and the previous
stat object:
import
watchFile
from
'node:fs'
watchFile
'message.text'
curr
prev
=>
console
log
`the current mtime is:
${
curr
mtime
console
log
`the previous mtime was:
${
prev
mtime
These stat objects are instances of
fs.Stat
. If the
bigint
option is
true
the numeric values in these objects are specified as
BigInt
s.
To be notified when the file was modified, not just accessed, it is necessary
to compare
curr.mtimeMs
and
prev.mtimeMs
When an
fs.watchFile
operation results in an
ENOENT
error, it
will invoke the listener once, with all the fields zeroed (or, for dates, the
Unix Epoch). If the file is created later on, the listener will be called
again, with the latest stat objects. This is a change in functionality since
v0.10.
Using
fs.watch()
is more efficient than
fs.watchFile
and
fs.unwatchFile
fs.watch
should be used instead of
fs.watchFile
and
fs.unwatchFile
when possible.
When a file being watched by
fs.watchFile()
disappears and reappears,
then the contents of
previous
in the second callback event (the file's
reappearance) will be the same as the contents of
previous
in the first
callback event (its disappearance).
This happens when:
the file is deleted, followed by a restore
the file is renamed and then renamed a second time back to its original name
fs.write(fd, buffer, offset[, length[, position]], callback)
Added in: v0.0.2
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v14.0.0
The
buffer
parameter won't coerce unsupported input to strings anymore.
v10.10.0
The
buffer
parameter can now be any
TypedArray
or a
DataView
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.4.0
The
buffer
parameter can now be a
Uint8Array
v7.2.0
The
offset
and
length
parameters are optional now.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
fd

buffer



offset

Default:
length

Default:
buffer.byteLength - offset
position


Default:
null
callback

err

bytesWritten

buffer



Write
buffer
to the file specified by
fd
offset
determines the part of the buffer to be written, and
length
is
an integer specifying the number of bytes to write.
position
refers to the offset from the beginning of the file where this data
should be written. If
typeof position !== 'number'
, the data will be written
at the current position. See
pwrite(2)
The callback will be given three arguments
(err, bytesWritten, buffer)
where
bytesWritten
specifies how many
bytes
were written from
buffer
If this method is invoked as its
util.promisify()
ed version, it returns
a promise for an
Object
with
bytesWritten
and
buffer
properties.
It is unsafe to use
fs.write()
multiple times on the same file without waiting
for the callback. For this scenario,
fs.createWriteStream()
is
recommended.
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.
fs.write(fd, buffer[, options], callback)
Added in: v18.3.0, v16.17.0
fd

buffer



options

offset

Default:
length

Default:
buffer.byteLength - offset
position


Default:
null
callback

err

bytesWritten

buffer



Write
buffer
to the file specified by
fd
Similar to the above
fs.write
function, this version takes an
optional
options
object. If no
options
object is specified, it will
default with the above values.
fs.write(fd, string[, position[, encoding]], callback)
Added in: v0.11.5
History
Version
Changes
v19.0.0
Passing to the
string
parameter an object with an own
toString
function is no longer supported.
v17.8.0
Passing to the
string
parameter an object with an own
toString
function is deprecated.
v14.12.0
The
string
parameter will stringify an object with an explicit
toString
function.
v14.0.0
The
string
parameter won't coerce unsupported input to strings anymore.
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.2.0
The
position
parameter is optional now.
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
fd

string

position


Default:
null
encoding

Default:
'utf8'
callback

err

written

string

Write
string
to the file specified by
fd
. If
string
is not a string,
an exception is thrown.
position
refers to the offset from the beginning of the file where this data
should be written. If
typeof position !== 'number'
the data will be written at
the current position. See
pwrite(2)
encoding
is the expected string encoding.
The callback will receive the arguments
(err, written, string)
where
written
specifies how many
bytes
the passed string required to be written. Bytes
written is not necessarily the same as string characters written. See
Buffer.byteLength
It is unsafe to use
fs.write()
multiple times on the same file without waiting
for the callback. For this scenario,
fs.createWriteStream()
is
recommended.
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.
On Windows, if the file descriptor is connected to the console (e.g.
fd == 1
or
stdout
) a string containing non-ASCII characters will not be rendered
properly by default, regardless of the encoding used.
It is possible to configure the console to render UTF-8 properly by changing the
active codepage with the
chcp 65001
command. See the
chcp
docs for more
details.
fs.writeFile(file, data[, options], callback)
Added in: v0.1.29
History
Version
Changes
v21.0.0, v20.10.0
The
flush
option is now supported.
v19.0.0
Passing to the
string
parameter an object with an own
toString
function is no longer supported.
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
v17.8.0
Passing to the
string
parameter an object with an own
toString
function is deprecated.
v16.0.0
The error returned may be an
AggregateError
if more than one error is returned.
v15.2.0, v14.17.0
The options argument may include an AbortSignal to abort an ongoing writeFile request.
v14.12.0
The
data
parameter will stringify an object with an explicit
toString
function.
v14.0.0
The
data
parameter won't coerce unsupported input to strings anymore.
v10.10.0
The
data
parameter can now be any
TypedArray
or a
DataView
v10.0.0
The
callback
parameter is no longer optional. Not passing it will throw a
TypeError
at runtime.
v7.4.0
The
data
parameter can now be a
Uint8Array
v7.0.0
The
callback
parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013.
v5.0.0
The
file
parameter can be a file descriptor now.
file




filename or file descriptor
data




options


encoding


Default:
'utf8'
mode

Default:
0o666
flag

See
support of file system
flags
Default:
'w'
flush

If all data is successfully written to the file, and
flush
is
true
fs.fsync()
is used to flush the data.
Default:
false
signal

allows aborting an in-progress writeFile
callback

err


When
file
is a filename, asynchronously writes data to the file, replacing the
file if it already exists.
data
can be a string or a buffer.
When
file
is a file descriptor, the behavior is similar to calling
fs.write()
directly (which is recommended). See the notes below on using
a file descriptor.
The
encoding
option is ignored if
data
is a buffer.
The
mode
option only affects the newly created file. See
fs.open()
for more details.
import
writeFile
from
'node:fs'
import
Buffer
from
'node:buffer'
const
data
new
Uint8Array
(Buffer
from
'Hello Node.js'
))
writeFile
'message.txt'
data
err
=>
if
(err)
throw
err
console
log
'The file has been saved!'
If
options
is a string, then it specifies the encoding:
import
writeFile
from
'node:fs'
writeFile
'message.txt'
'Hello Node.js'
'utf8'
callback)
It is unsafe to use
fs.writeFile()
multiple times on the same file without
waiting for the callback. For this scenario,
fs.createWriteStream()
is
recommended.
Similarly to
fs.readFile
fs.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()
It is possible to use an

to cancel an
fs.writeFile()
Cancelation is "best effort", and some amount of data is likely still
to be written.
import
writeFile
from
'node:fs'
import
Buffer
from
'node:buffer'
const
controller
new
AbortController
()
const
signal
controller
const
data
new
Uint8Array
(Buffer
from
'Hello Node.js'
))
writeFile
'message.txt'
data
signal
},
err
=>
// When a request is aborted - the callback is called with an AbortError
// When the request should be aborted
controller
abort
()
Aborting an ongoing request does not abort individual operating
system requests but rather the internal buffering
fs.writeFile
performs.
Using
fs.writeFile()
with file descriptors
When
file
is a file descriptor, the behavior is almost identical to directly
calling
fs.write()
like:
import
write
from
'node:fs'
import
Buffer
from
'node:buffer'
write
(fd
Buffer
from
(data
options
encoding)
callback)
The difference from directly calling
fs.write()
is that under some unusual
conditions,
fs.write()
might write only part of the buffer and need to be
retried to write the remaining data, whereas
fs.writeFile()
retries until
the data is entirely written (or an error occurs).
The implications of this are a common source of confusion. In
the file descriptor case, the file is not replaced! The data is not necessarily
written to the beginning of the file, and the file's original data may remain
before and/or after the newly written data.
For example, if
fs.writeFile()
is called twice in a row, first to write the
string
'Hello'
, then to write the string
', World'
, the file would contain
'Hello, World'
, and might contain some of the file's original data (depending
on the size of the original file, and the position of the file descriptor). If
a file name had been used instead of a descriptor, the file would be guaranteed
to contain only
', World'
fs.writev(fd, buffers[, position], callback)
Added in: v12.9.0
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
fd

buffers

position


Default:
null
callback

err

bytesWritten

buffers

Write an array of
ArrayBufferView
s to the file specified by
fd
using
writev()
position
is the offset from the beginning of the file where this data
should be written. If
typeof position !== 'number'
, the data will be written
at the current position.
The callback will be given three arguments:
err
bytesWritten
, and
buffers
bytesWritten
is how many bytes were written from
buffers
If this method is
util.promisify()
ed, it returns a promise for an
Object
with
bytesWritten
and
buffers
properties.
It is unsafe to use
fs.writev()
multiple times on the same file without
waiting for the callback. For this scenario, use
fs.createWriteStream()
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.
Synchronous API
The synchronous APIs perform all operations synchronously, blocking the
event loop until the operation completes or fails.
fs.accessSync(path[, mode])
Added in: v0.11.15
History
Version
Changes
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



mode

Default:
fs.constants.F_OK
Synchronously 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 any of the accessibility checks fail, an
Error
will be thrown. Otherwise,
the method will return
undefined
import
accessSync
constants
from
'node:fs'
try
accessSync
'etc/passwd'
constants
R_OK
constants
W_OK
console
log
'can read/write'
catch
(err)
console
error
'no access!'
fs.appendFileSync(path, data[, options])
Added in: v0.6.7
History
Version
Changes
v21.1.0, v20.10.0
The
flush
option is now supported.
v7.0.0
The passed
options
object will never be modified.
v5.0.0
The
file
parameter can be a file descriptor now.
path




filename or file descriptor
data


options


encoding


Default:
'utf8'
mode

Default:
0o666
flag

See
support of file system
flags
Default:
'a'
flush

If
true
, the underlying file descriptor is flushed
prior to closing it.
Default:
false
Synchronously append data to a file, creating the file if it does not yet
exist.
data
can be a string or a

The
mode
option only affects the newly created file. See
fs.open()
for more details.
import
appendFileSync
from
'node:fs'
try
appendFileSync
'message.txt'
'data to append'
console
log
'The "data to append" was appended to file!'
catch
(err)
/* Handle the error */
If
options
is a string, then it specifies the encoding:
import
appendFileSync
from
'node:fs'
appendFileSync
'message.txt'
'data to append'
'utf8'
The
path
may be specified as a numeric file descriptor that has been opened
for appending (using
fs.open()
or
fs.openSync()
). The file descriptor will
not be closed automatically.
import
openSync
closeSync
appendFileSync
from
'node:fs'
let
fd
try
fd
openSync
'message.txt'
'a'
appendFileSync
(fd
'data to append'
'utf8'
catch
(err)
/* Handle the error */
finally
if
(fd
!==
undefined
closeSync
(fd)
fs.chmodSync(path, mode)
Added in: v0.6.7
History
Version
Changes
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



mode


For detailed information, see the documentation of the asynchronous version of
this API:
fs.chmod()
See the POSIX
chmod(2)
documentation for more detail.
fs.chownSync(path, uid, gid)
Added in: v0.1.97
History
Version
Changes
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



uid

gid

Synchronously changes owner and group of a file. Returns
undefined
This is the synchronous version of
fs.chown()
See the POSIX
chown(2)
documentation for more detail.
fs.closeSync(fd)
Added in: v0.1.21
fd

Closes the file descriptor. Returns
undefined
Calling
fs.closeSync()
on any file descriptor (
fd
) that is currently in use
through any other
fs
operation may lead to undefined behavior.
See the POSIX
close(2)
documentation for more detail.
fs.copyFileSync(src, dest[, mode])
Added in: v8.5.0
History
Version
Changes
v14.0.0
Changed
flags
argument to
mode
and imposed stricter type validation.
src



source filename to copy
dest



destination filename of the copy operation
mode

modifiers for copy operation.
Default:
Synchronously copies
src
to
dest
. By default,
dest
is overwritten if it
already exists. Returns
undefined
. Node.js makes no guarantees about the
atomicity of the copy operation. If an error occurs after the destination file
has been opened for writing, Node.js will attempt to remove the destination.
mode
is an optional integer that specifies 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
).
fs.constants.COPYFILE_EXCL
: The copy operation will fail if
dest
already
exists.
fs.constants.COPYFILE_FICLONE
: The copy operation will attempt to create a
copy-on-write reflink. If the platform does not support copy-on-write, then a
fallback copy mechanism is used.
fs.constants.COPYFILE_FICLONE_FORCE
: The copy operation will attempt to
create a copy-on-write reflink. If the platform does not support
copy-on-write, then the operation will fail.
import
copyFileSync
constants
from
'node:fs'
// destination.txt will be created or overwritten by default.
copyFileSync
'source.txt'
'destination.txt'
console
log
'source.txt was copied to destination.txt'
// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.
copyFileSync
'source.txt'
'destination.txt'
constants
COPYFILE_EXCL
fs.cpSync(src, dest[, options])
Added in: v16.7.0
History
Version
Changes
v22.3.0
This API is no longer experimental.
v20.1.0, v18.17.0
Accept an additional
mode
option to specify the copy behavior as the
mode
argument of
fs.copyFile()
v17.6.0, v16.15.0
Accepts an additional
verbatimSymlinks
option to specify whether to perform path resolution for symlinks.
src


source path to copy.
dest


destination path to copy to.
options

dereference

dereference symlinks.
Default:
false
errorOnExist

when
force
is
false
, and the destination
exists, throw an error.
Default:
false
filter

Function to filter copied files/directories. Return
true
to copy the item,
false
to ignore it. When ignoring a directory,
all of its contents will be skipped as well.
Default:
undefined
src

source path to copy.
dest

destination path to copy to.
Returns:

Any non-
Promise
value that is coercible
to
boolean
force

overwrite existing file or directory. The copy
operation will ignore errors if you set this to false and the destination
exists. Use the
errorOnExist
option to change this behavior.
Default:
true
mode

modifiers for copy operation.
Default:
See
mode
flag of
fs.copyFileSync()
preserveTimestamps

When
true
timestamps from
src
will
be preserved.
Default:
false
recursive

copy directories recursively
Default:
false
verbatimSymlinks

When
true
, path resolution for symlinks will
be skipped.
Default:
false
Synchronously 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/
fs.existsSync(path)
Added in: v0.1.21
History
Version
Changes
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



Returns:

Returns
true
if the path exists,
false
otherwise.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.exists()
fs.exists()
is deprecated, but
fs.existsSync()
is not. The
callback
parameter to
fs.exists()
accepts parameters that are inconsistent with other
Node.js callbacks.
fs.existsSync()
does not use a callback.
import
existsSync
from
'node:fs'
if
existsSync
'/etc/passwd'
))
console
log
'The path exists.'
fs.fchmodSync(fd, mode)
Added in: v0.4.7
fd

mode


Sets the permissions on the file. Returns
undefined
See the POSIX
fchmod(2)
documentation for more detail.
fs.fchownSync(fd, uid, gid)
Added in: v0.4.7
fd

uid

The file's new owner's user id.
gid

The file's new group's group id.
Sets the owner of the file. Returns
undefined
See the POSIX
fchown(2)
documentation for more detail.
fs.fdatasyncSync(fd)
Added in: v0.1.96
fd

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. Returns
undefined
fs.fstatSync(fd[, options])
Added in: v0.1.95
History
Version
Changes
v10.5.0
Accepts an additional
options
object to specify whether the numeric values returned should be bigint.
fd

options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
Returns:

Retrieves the

for the file descriptor.
See the POSIX
fstat(2)
documentation for more detail.
fs.fsyncSync(fd)
Added in: v0.1.96
fd

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
undefined
fs.ftruncateSync(fd[, len])
Added in: v0.8.6
fd

len

Default:
Truncates the file descriptor. Returns
undefined
For detailed information, see the documentation of the asynchronous version of
this API:
fs.ftruncate()
fs.futimesSync(fd, atime, mtime)
Added in: v0.4.2
History
Version
Changes
v4.1.0
Numeric strings,
NaN
, and
Infinity
are now allowed time specifiers.
fd

atime



mtime



Synchronous version of
fs.futimes()
. Returns
undefined
fs.globSync(pattern[, options])
Added in: v22.0.0
History
Version
Changes
v24.1.0, v22.17.0
Add support for
URL
instances for
cwd
option.
v24.0.0, v22.17.0
Marking the API stable.
v23.7.0, v22.14.0
Add support for
exclude
option to accept glob patterns.
v22.2.0
Add support for
withFileTypes
as an option.
pattern


options

cwd


current working directory.
Default:
process.cwd()
exclude


Function to filter out files/directories or a
list of glob patterns to be excluded. If a function is provided, return
true
to exclude the item,
false
to include it.
Default:
undefined
withFileTypes

true
if the glob should return paths as Dirents,
false
otherwise.
Default:
false
Returns:

paths of files that match the pattern.
import
globSync
from
'node:fs'
console
log
globSync
'**/*.js'
))
const
globSync
require
'node:fs'
console
log
globSync
'**/*.js'
))
fs.lchmodSync(path, mode)
Deprecated in: v0.4.7
Stability: 0 - Deprecated
path



mode

Changes the permissions on a symbolic link. Returns
undefined
This method is only implemented on macOS.
See the POSIX
lchmod(2)
documentation for more detail.
fs.lchownSync(path, uid, gid)
History
Version
Changes
v10.6.0
This API is no longer deprecated.
v0.4.7
Documentation-only deprecation.
path



uid

The file's new owner's user id.
gid

The file's new group's group id.
Set the owner for the path. Returns
undefined
See the POSIX
lchown(2)
documentation for more details.
fs.lutimesSync(path, atime, mtime)
Added in: v14.5.0, v12.19.0
path



atime



mtime



Change the file system timestamps of the symbolic link referenced by
path
Returns
undefined
, or throws an exception when parameters are incorrect or
the operation fails. This is the synchronous version of
fs.lutimes()
fs.linkSync(existingPath, newPath)
Added in: v0.1.31
History
Version
Changes
v7.6.0
The
existingPath
and
newPath
parameters can be WHATWG
URL
objects using
file:
protocol. Support is currently still
experimental
existingPath



newPath



Creates a new link from the
existingPath
to the
newPath
. See the POSIX
link(2)
documentation for more detail. Returns
undefined
fs.lstatSync(path[, options])
Added in: v0.1.30
History
Version
Changes
v15.3.0, v14.17.0
Accepts a
throwIfNoEntry
option to specify whether an exception should be thrown if the entry does not exist.
v10.5.0
Accepts an additional
options
object to specify whether the numeric values returned should be bigint.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
throwIfNoEntry

Whether an exception will be thrown
if no file system entry exists, rather than returning
undefined
Default:
true
Returns:

Retrieves the

for the symbolic link referred to by
path
See the POSIX
lstat(2)
documentation for more details.
fs.mkdirSync(path[, options])
Added in: v0.1.21
History
Version
Changes
v13.11.0, v12.17.0
In
recursive
mode, the first created path is returned now.
v10.12.0
The second argument can now be an
options
object with
recursive
and
mode
properties.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



options


recursive

Default:
false
mode


Not supported on Windows.
Default:
0o777
Returns:


Synchronously creates a directory. Returns
undefined
, or if
recursive
is
true
, the first directory path created.
This is the synchronous version of
fs.mkdir()
See the POSIX
mkdir(2)
documentation for more details.
fs.mkdtempSync(prefix[, options])
Added in: v5.10.0
History
Version
Changes
v20.6.0, v18.19.0
The
prefix
parameter now accepts buffers and URL.
v16.5.0, v14.18.0
The
prefix
parameter now accepts an empty string.
prefix



options


encoding

Default:
'utf8'
Returns:

Returns the created directory path.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.mkdtemp()
The optional
options
argument can be a string specifying an encoding, or an
object with an
encoding
property specifying the character encoding to use.
fs.mkdtempDisposableSync(prefix[, options])
Added in: v24.4.0
prefix



options


encoding

Default:
'utf8'
Returns:

A disposable object:
path

The path of the created directory.
remove

A function which removes the created directory.
[Symbol.dispose]

The same as
remove
Returns a disposable object whose
path
property holds the created directory
path. When the object is disposed, the directory and its contents will be
removed if it still exists. If the directory cannot be deleted, disposal will
throw an error. The object has a
remove()
method which will perform the same
task.
For detailed information, see the documentation of
fs.mkdtemp()
There is no callback-based version of this API because it is designed for use
with the
using
syntax.
The optional
options
argument can be a string specifying an encoding, or an
object with an
encoding
property specifying the character encoding to use.
fs.opendirSync(path[, options])
Added in: v12.12.0
History
Version
Changes
v20.1.0, v18.17.0
Added
recursive
option.
v13.1.0, v12.16.0
The
bufferSize
option was introduced.
path



options

encoding


Default:
'utf8'
bufferSize

Number of directory entries that are buffered
internally when reading from the directory. Higher values lead to better
performance but higher memory usage.
Default:
32
recursive

Default:
false
Returns:

Synchronously open a directory. See
opendir(3)
Creates an

, 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.
fs.openSync(path[, flags[, mode]])
Added in: v0.1.21
History
Version
Changes
v11.1.0
The
flags
argument is now optional and defaults to
'r'
v9.9.0
The
as
and
as+
flags are supported now.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



flags


Default:
'r'
See
support of file system
flags
mode


Default:
0o666
Returns:

Returns an integer representing the file descriptor.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.open()
fs.readdirSync(path[, options])
Added in: v0.1.21
History
Version
Changes
v20.1.0, v18.17.0
Added
recursive
option.
v10.10.0
New option
withFileTypes
was added.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



options


encoding

Default:
'utf8'
withFileTypes

Default:
false
recursive

If
true
, reads the contents of a directory
recursively. In recursive mode, it will list all files, sub files, and
directories.
Default:
false
Returns:



Reads the contents of the directory.
See the POSIX
readdir(3)
documentation for more details.
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 returned. If the
encoding
is set to
'buffer'
the filenames returned will be passed as

objects.
If
options.withFileTypes
is set to
true
, the result will contain

objects.
fs.readFileSync(path[, options])
Added in: v0.1.8
History
Version
Changes
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v5.0.0
The
path
parameter can be a file descriptor now.
path




filename or file descriptor
options


encoding


Default:
null
flag

See
support of file system
flags
Default:
'r'
Returns:


Returns the contents of the
path
For detailed information, see the documentation of the asynchronous version of
this API:
fs.readFile()
If the
encoding
option is specified then this function returns a
string. Otherwise it returns a buffer.
Similar to
fs.readFile()
, when the path is a directory, the behavior of
fs.readFileSync()
is platform-specific.
import
readFileSync
from
'node:fs'
// macOS, Linux, and Windows
readFileSync
''
// => [Error: EISDIR: illegal operation on a directory, read ]
// FreeBSD
readFileSync
''
// =>
fs.readlinkSync(path[, options])
Added in: v0.1.31
History
Version
Changes
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



options


encoding

Default:
'utf8'
Returns:


Returns the symbolic link's string value.
See the POSIX
readlink(2)
documentation for more details.
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

object.
fs.readSync(fd, buffer, offset, length[, position])
Added in: v0.1.21
History
Version
Changes
v10.10.0
The
buffer
parameter can now be any
TypedArray
or a
DataView
v6.0.0
The
length
parameter can now be
fd

buffer



offset

length

position



Default:
null
Returns:

Returns the number of
bytesRead
For detailed information, see the documentation of the asynchronous version of
this API:
fs.read()
fs.readSync(fd, buffer[, options])
Added in: v13.13.0, v12.17.0
History
Version
Changes
v13.13.0, v12.17.0
Options object can be passed in to make offset, length, and position optional.
fd

buffer



options

offset

Default:
length

Default:
buffer.byteLength - offset
position



Default:
null
Returns:

Returns the number of
bytesRead
Similar to the above
fs.readSync
function, this version takes an optional
options
object.
If no
options
object is specified, it will default with the above values.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.read()
fs.readvSync(fd, buffers[, position])
Added in: v13.13.0, v12.17.0
fd

buffers

position


Default:
null
Returns:

The number of bytes read.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.readv()
fs.realpathSync(path[, options])
Added in: v0.1.31
History
Version
Changes
v8.0.0
Pipe/Socket resolve support was added.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v6.4.0
Calling
realpathSync
now works again for various edge cases on Windows.
v6.0.0
The
cache
parameter was removed.
path



options


encoding

Default:
'utf8'
Returns:


Returns the resolved pathname.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.realpath()
fs.realpathSync.native(path[, options])
Added in: v9.2.0
path



options


encoding

Default:
'utf8'
Returns:


Synchronous
realpath(3)
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 returned. If the
encoding
is set to
'buffer'
the path returned will be passed as a

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.
fs.renameSync(oldPath, newPath)
Added in: v0.1.21
History
Version
Changes
v7.6.0
The
oldPath
and
newPath
parameters can be WHATWG
URL
objects using
file:
protocol. Support is currently still
experimental
oldPath



newPath



Renames the file from
oldPath
to
newPath
. Returns
undefined
See the POSIX
rename(2)
documentation for more details.
fs.rmdirSync(path[, options])
Added in: v0.1.21
History
Version
Changes
v25.0.0
Remove
recursive
option.
v16.0.0
Using
fs.rmdirSync(path, { recursive: true })
on a
path
that is a file is no longer permitted and results in an
ENOENT
error on Windows and an
ENOTDIR
error on POSIX.
v16.0.0
Using
fs.rmdirSync(path, { recursive: true })
on a
path
that does not exist is no longer permitted and results in a
ENOENT
error.
v16.0.0
The
recursive
option is deprecated, using it triggers a deprecation warning.
v14.14.0
The
recursive
option is deprecated, use
fs.rmSync
instead.
v13.3.0, v12.16.0
The
maxBusyTries
option is renamed to
maxRetries
, and its default is 0. The
emfileWait
option has been removed, and
EMFILE
errors use the same retry logic as other errors. The
retryDelay
option is now supported.
ENFILE
errors are now retried.
v12.10.0
The
recursive
maxBusyTries
, and
emfileWait
options are now supported.
v7.6.0
The
path
parameters can be a WHATWG
URL
object using
file:
protocol.
path



options

There are currently no options exposed. There used to
be options for
recursive
maxBusyTries
, and
emfileWait
but they were
deprecated and removed. The
options
argument is still accepted for
backwards compatibility but it is not used.
Synchronous
rmdir(2)
. Returns
undefined
Using
fs.rmdirSync()
on a file (not a directory) results in an
ENOENT
error
on Windows and an
ENOTDIR
error on POSIX.
To get a behavior similar to the
rm -rf
Unix command, use
fs.rmSync()
with options
{ recursive: true, force: true }
fs.rmSync(path[, options])
Added in: v14.14.0
History
Version
Changes
v17.3.0, v16.14.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



options

force

When
true
, exceptions will be ignored if
path
does
not exist.
Default:
false
maxRetries

If an
EBUSY
EMFILE
ENFILE
ENOTEMPTY
, or
EPERM
error is encountered, Node.js will retry the operation with a linear
backoff wait of
retryDelay
milliseconds longer on each try. This option
represents the number of retries. This option is ignored if the
recursive
option is not
true
Default:
recursive

If
true
, perform a recursive directory removal. In
recursive mode operations are retried on failure.
Default:
false
retryDelay

The amount of time in milliseconds to wait between
retries. This option is ignored if the
recursive
option is not
true
Default:
100
Synchronously removes files and directories (modeled on the standard POSIX
rm
utility). Returns
undefined
fs.statSync(path[, options])
Added in: v0.1.21
History
Version
Changes
v15.3.0, v14.17.0
Accepts a
throwIfNoEntry
option to specify whether an exception should be thrown if the entry does not exist.
v10.5.0
Accepts an additional
options
object to specify whether the numeric values returned should be bigint.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
throwIfNoEntry

Whether an exception will be thrown
if no file system entry exists, rather than returning
undefined
Default:
true
Returns:

Retrieves the

for the path.
fs.statfsSync(path[, options])
Added in: v19.6.0, v18.15.0
path



options

bigint

Whether the numeric values in the returned

object should be
bigint
Default:
false
Returns:

Synchronous
statfs(2)
. Returns information about the mounted file system which
contains
path
In case of an error, the
err.code
will be one of
Common System Errors
fs.symlinkSync(target, path[, type])
Added in: v0.1.31
History
Version
Changes
v12.0.0
If the
type
argument is left undefined, Node will autodetect
target
type and automatically select
dir
or
file
v7.6.0
The
target
and
path
parameters can be WHATWG
URL
objects using
file:
protocol. Support is currently still
experimental
target



path



type


Default:
null
Returns:
undefined
For detailed information, see the documentation of the asynchronous version of
this API:
fs.symlink()
fs.truncateSync(path[, len])
Added in: v0.8.6
path



len

Default:
Truncates the file. Returns
undefined
. A file descriptor can also be
passed as the first argument. In this case,
fs.ftruncateSync()
is called.
Passing a file descriptor is deprecated and may result in an error being thrown
in the future.
fs.unlinkSync(path)
Added in: v0.1.21
History
Version
Changes
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
path



Synchronous
unlink(2)
. Returns
undefined
fs.utimesSync(path, atime, mtime)
Added in: v0.4.2
History
Version
Changes
v8.0.0
NaN
Infinity
, and
-Infinity
are no longer valid time specifiers.
v7.6.0
The
path
parameter can be a WHATWG
URL
object using
file:
protocol.
v4.1.0
Numeric strings,
NaN
, and
Infinity
are now allowed time specifiers.
path



atime



mtime



Returns:
undefined
For detailed information, see the documentation of the asynchronous version of
this API:
fs.utimes()
fs.writeFileSync(file, data[, options])
Added in: v0.1.29
History
Version
Changes
v21.0.0, v20.10.0
The
flush
option is now supported.
v19.0.0
Passing to the
data
parameter an object with an own
toString
function is no longer supported.
v17.8.0
Passing to the
data
parameter an object with an own
toString
function is deprecated.
v14.12.0
The
data
parameter will stringify an object with an explicit
toString
function.
v14.0.0
The
data
parameter won't coerce unsupported input to strings anymore.
v10.10.0
The
data
parameter can now be any
TypedArray
or a
DataView
v7.4.0
The
data
parameter can now be a
Uint8Array
v5.0.0
The
file
parameter can be a file descriptor now.
file




filename or file descriptor
data




options


encoding


Default:
'utf8'
mode

Default:
0o666
flag

See
support of file system
flags
Default:
'w'
flush

If all data is successfully written to the file, and
flush
is
true
fs.fsyncSync()
is used to flush the data.
Returns:
undefined
The
mode
option only affects the newly created file. See
fs.open()
for more details.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.writeFile()
fs.writeSync(fd, buffer, offset[, length[, position]])
Added in: v0.1.21
History
Version
Changes
v14.0.0
The
buffer
parameter won't coerce unsupported input to strings anymore.
v10.10.0
The
buffer
parameter can now be any
TypedArray
or a
DataView
v7.4.0
The
buffer
parameter can now be a
Uint8Array
v7.2.0
The
offset
and
length
parameters are optional now.
fd

buffer



offset

Default:
length

Default:
buffer.byteLength - offset
position


Default:
null
Returns:

The number of bytes written.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.write(fd, buffer...)
fs.writeSync(fd, buffer[, options])
Added in: v18.3.0, v16.17.0
fd

buffer



options

offset

Default:
length

Default:
buffer.byteLength - offset
position


Default:
null
Returns:

The number of bytes written.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.write(fd, buffer...)
fs.writeSync(fd, string[, position[, encoding]])
Added in: v0.11.5
History
Version
Changes
v14.0.0
The
string
parameter won't coerce unsupported input to strings anymore.
v7.2.0
The
position
parameter is optional now.
fd

string

position


Default:
null
encoding

Default:
'utf8'
Returns:

The number of bytes written.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.write(fd, string...)
fs.writevSync(fd, buffers[, position])
Added in: v12.9.0
fd

buffers

position


Default:
null
Returns:

The number of bytes written.
For detailed information, see the documentation of the asynchronous version of
this API:
fs.writev()
Common Objects
The common objects are shared by all of the file system API variants
(promise, callback, and synchronous).
Class:
fs.Dir
Added in: v12.12.0
A class representing a directory stream.
Created by
fs.opendir()
fs.opendirSync()
, or
fsPromises.opendir()
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

object will be automatically
closed after the iterator exits.
dir.close()
Added in: v12.12.0
Returns:

Asynchronously close the directory's underlying resource handle.
Subsequent reads will result in errors.
A promise is returned that will be fulfilled after the resource has been
closed.
dir.close(callback)
Added in: v12.12.0
History
Version
Changes
v18.0.0
Passing an invalid callback to the
callback
argument now throws
ERR_INVALID_ARG_TYPE
instead of
ERR_INVALID_CALLBACK
callback

err

Asynchronously close the directory's underlying resource handle.
Subsequent reads will result in errors.
The
callback
will be called after the resource handle has been closed.
dir.closeSync()
Added in: v12.12.0
Synchronously close the directory's underlying resource handle.
Subsequent reads will result in errors.
dir.path
Added in: v12.12.0
Type:

The read-only path of this directory as was provided to
fs.opendir()
fs.opendirSync()
, or
fsPromises.opendir()
dir.read()
Added in: v12.12.0
Returns:

Fulfills with a


Asynchronously read the next directory entry via
readdir(3)
as an

A promise is returned that will be fulfilled with an

, or
null
if there are no more directory entries to read.
Directory entries returned by this function are in no particular order as
provided by the operating system's underlying directory mechanisms.
Entries added or removed while iterating over the directory might not be
included in the iteration results.
dir.read(callback)
Added in: v12.12.0
callback

err

dirent


Asynchronously read the next directory entry via
readdir(3)
as an

After the read is completed, the
callback
will be called with an

, or
null
if there are no more directory entries to read.
Directory entries returned by this function are in no particular order as
provided by the operating system's underlying directory mechanisms.
Entries added or removed while iterating over the directory might not be
included in the iteration results.
dir.readSync()
Added in: v12.12.0
Returns:


Synchronously read the next directory entry as an

. See the
POSIX
readdir(3)
documentation for more detail.
If there are no more directory entries to read,
null
will be returned.
Directory entries returned by this function are in no particular order as
provided by the operating system's underlying directory mechanisms.
Entries added or removed while iterating over the directory might not be
included in the iteration results.
dir[Symbol.asyncIterator]()
Added in: v12.12.0
Returns:

An AsyncIterator of

Asynchronously iterates over the directory until all entries have
been read. Refer to the POSIX
readdir(3)
documentation for more detail.
Entries returned by the async iterator are always an

The
null
case from
dir.read()
is handled internally.
See

for an example.
Directory entries returned by this iterator are in no particular order as
provided by the operating system's underlying directory mechanisms.
Entries added or removed while iterating over the directory might not be
included in the iteration results.
dir[Symbol.asyncDispose]()
Added in: v24.1.0, v22.1.0
History
Version
Changes
v24.2.0
No longer experimental.
Calls
dir.close()
if the directory handle is open, and returns a promise that
fulfills when disposal is complete.
dir[Symbol.dispose]()
Added in: v24.1.0, v22.1.0
History
Version
Changes
v24.2.0
No longer experimental.
Calls
dir.closeSync()
if the directory handle is open, and returns
undefined
Class:
fs.Dirent
Added in: v10.10.0
A representation of a directory entry, which can be a file or a subdirectory
within the directory, as returned by reading from an

. The
directory entry is a combination of the file name and file type pairs.
Additionally, when
fs.readdir()
or
fs.readdirSync()
is called with
the
withFileTypes
option set to
true
, the resulting array is filled with

objects, rather than strings or

s.
dirent.isBlockDevice()
Added in: v10.10.0
Returns:

Returns
true
if the

object describes a block device.
dirent.isCharacterDevice()
Added in: v10.10.0
Returns:

Returns
true
if the

object describes a character device.
dirent.isDirectory()
Added in: v10.10.0
Returns:

Returns
true
if the

object describes a file system
directory.
dirent.isFIFO()
Added in: v10.10.0
Returns:

Returns
true
if the

object describes a first-in-first-out
(FIFO) pipe.
dirent.isFile()
Added in: v10.10.0
Returns:

Returns
true
if the

object describes a regular file.
dirent.isSocket()
Added in: v10.10.0
Returns:

Returns
true
if the

object describes a socket.
dirent.isSymbolicLink()
Added in: v10.10.0
Returns:

Returns
true
if the

object describes a symbolic link.
dirent.name
Added in: v10.10.0
Type:


The file name that this

object refers to. The type of this
value is determined by the
options.encoding
passed to
fs.readdir()
or
fs.readdirSync()
dirent.parentPath
Added in: v21.4.0, v20.12.0, v18.20.0
History
Version
Changes
v24.0.0, v22.17.0
Marking the API stable.
Type:

The path to the parent directory of the file this

object refers to.
Class:
fs.FSWatcher
Added in: v0.5.8
Extends

A successful call to
fs.watch()
method will return a new

object.
All

objects emit a
'change'
event whenever a specific watched
file is modified.
Event:
'change'
Added in: v0.5.8
eventType

The type of change event that has occurred
filename


The filename that changed (if relevant/available)
Emitted when something changes in a watched directory or file.
See more details in
fs.watch()
The
filename
argument may not be provided depending on operating system
support. If
filename
is provided, it will be provided as a

if
fs.watch()
is called with its
encoding
option set to
'buffer'
, otherwise
filename
will be a UTF-8 string.
import
watch
from
'node:fs'
// Example when handled through fs.watch() listener
watch
'./tmp'
encoding
'buffer'
},
eventType
filename
=>
if
(filename)
console
log
(filename)
// Prints:
Event:
'close'
Added in: v10.0.0
Emitted when the watcher stops watching for changes. The closed

object is no longer usable in the event handler.
Event:
'error'
Added in: v0.5.8
error

Emitted when an error occurs while watching the file. The errored

object is no longer usable in the event handler.
watcher.close()
Added in: v0.5.8
Stop watching for changes on the given

. Once stopped, the

object is no longer usable.
watcher.ref()
Added in: v14.3.0, v12.20.0
Returns:

When called, requests that the Node.js event loop
not
exit so long as the

is active. Calling
watcher.ref()
multiple times will have
no effect.
By default, all

objects are "ref'ed", making it normally
unnecessary to call
watcher.ref()
unless
watcher.unref()
had been
called previously.
watcher.unref()
Added in: v14.3.0, v12.20.0
Returns:

When called, the active

object will not require the Node.js
event loop to remain active. If there is no other activity keeping the
event loop running, the process may exit before the

object's
callback is invoked. Calling
watcher.unref()
multiple times will have
no effect.
Class:
fs.StatWatcher
Added in: v14.3.0, v12.20.0
Extends

A successful call to
fs.watchFile()
method will return a new

object.
watcher.ref()
Added in: v14.3.0, v12.20.0
Returns:

When called, requests that the Node.js event loop
not
exit so long as the

is active. Calling
watcher.ref()
multiple times will have
no effect.
By default, all

objects are "ref'ed", making it normally
unnecessary to call
watcher.ref()
unless
watcher.unref()
had been
called previously.
watcher.unref()
Added in: v14.3.0, v12.20.0
Returns:

When called, the active

object will not require the Node.js
event loop to remain active. If there is no other activity keeping the
event loop running, the process may exit before the

object's
callback is invoked. Calling
watcher.unref()
multiple times will have
no effect.
Class:
fs.ReadStream
Added in: v0.1.93
Extends:

Instances of

cannot be constructed directly. They are created and
returned using the
fs.createReadStream()
function.
Event:
'close'
Added in: v0.1.93
Emitted when the

's underlying file descriptor has been closed.
Event:
'open'
Added in: v0.1.93
fd

Integer file descriptor used by the

Emitted when the

's file descriptor has been opened.
Event:
'ready'
Added in: v9.11.0
Emitted when the

is ready to be used.
Fires immediately after
'open'
readStream.bytesRead
Added in: v6.4.0
Type:

The number of bytes that have been read so far.
readStream.path
Added in: v0.1.93
Type:


The path to the file the stream is reading from as specified in the first
argument to
fs.createReadStream()
. If
path
is passed as a string, then
readStream.path
will be a string. If
path
is passed as a

, then
readStream.path
will be a

. If
fd
is specified, then
readStream.path
will be
undefined
readStream.pending
Added in: v11.2.0, v10.16.0
Type:

This property is
true
if the underlying file has not been opened yet,
i.e. before the
'ready'
event is emitted.
Class:
fs.Stats
Added in: v0.1.21
History
Version
Changes
v22.0.0, v20.13.0
Public constructor is deprecated.
v8.1.0
Added times as numbers.

object provides information about a file.
Objects returned from
fs.stat()
fs.lstat()
fs.fstat()
, and
their synchronous counterparts are of this type.
If
bigint
in the
options
passed to those methods is true, the numeric values
will be
bigint
instead of
number
, and the object will contain additional
nanosecond-precision properties suffixed with
Ns
Stat
objects are not to be created directly using the
new
keyword.
Stats {
dev: 2114,
ino: 48064969,
mode: 33188,
nlink: 1,
uid: 85,
gid: 100,
rdev: 0,
size: 527,
blksize: 4096,
blocks: 8,
atimeMs: 1318289051000.1,
mtimeMs: 1318289051000.1,
ctimeMs: 1318289051000.1,
birthtimeMs: 1318289051000.1,
atime: Mon, 10 Oct 2011 23:24:11 GMT,
mtime: Mon, 10 Oct 2011 23:24:11 GMT,
ctime: Mon, 10 Oct 2011 23:24:11 GMT,
birthtime: Mon, 10 Oct 2011 23:24:11 GMT }
bigint
version:
BigIntStats {
dev: 2114n,
ino: 48064969n,
mode: 33188n,
nlink: 1n,
uid: 85n,
gid: 100n,
rdev: 0n,
size: 527n,
blksize: 4096n,
blocks: 8n,
atimeMs: 1318289051000n,
mtimeMs: 1318289051000n,
ctimeMs: 1318289051000n,
birthtimeMs: 1318289051000n,
atimeNs: 1318289051000000000n,
mtimeNs: 1318289051000000000n,
ctimeNs: 1318289051000000000n,
birthtimeNs: 1318289051000000000n,
atime: Mon, 10 Oct 2011 23:24:11 GMT,
mtime: Mon, 10 Oct 2011 23:24:11 GMT,
ctime: Mon, 10 Oct 2011 23:24:11 GMT,
birthtime: Mon, 10 Oct 2011 23:24:11 GMT }
stats.isBlockDevice()
Added in: v0.1.10
Returns:

Returns
true
if the

object describes a block device.
stats.isCharacterDevice()
Added in: v0.1.10
Returns:

Returns
true
if the

object describes a character device.
stats.isDirectory()
Added in: v0.1.10
Returns:

Returns
true
if the

object describes a file system directory.
If the

object was obtained from calling
fs.lstat()
on a
symbolic link which resolves to a directory, this method will return
false
This is because
fs.lstat()
returns information
about a symbolic link itself and not the path it resolves to.
stats.isFIFO()
Added in: v0.1.10
Returns:

Returns
true
if the

object describes a first-in-first-out (FIFO)
pipe.
stats.isFile()
Added in: v0.1.10
Returns:

Returns
true
if the

object describes a regular file.
stats.isSocket()
Added in: v0.1.10
Returns:

Returns
true
if the

object describes a socket.
stats.isSymbolicLink()
Added in: v0.1.10
Returns:

Returns
true
if the

object describes a symbolic link.
This method is only valid when using
fs.lstat()
stats.dev
Type:


The numeric identifier of the device containing the file.
stats.ino
Type:


The file system specific "Inode" number for the file.
stats.mode
Type:


A bit-field describing the file type and mode.
stats.nlink
Type:


The number of hard-links that exist for the file.
stats.uid
Type:


The numeric user identifier of the user that owns the file (POSIX).
stats.gid
Type:


The numeric group identifier of the group that owns the file (POSIX).
stats.rdev
Type:


A numeric device identifier if the file represents a device.
stats.size
Type:


The size of the file in bytes.
If the underlying file system does not support getting the size of the file,
this will be
stats.blksize
Type:


The file system block size for i/o operations.
stats.blocks
Type:


The number of blocks allocated for this file.
stats.atimeMs
Added in: v8.1.0
Type:


The timestamp indicating the last time this file was accessed expressed in
milliseconds since the POSIX Epoch.
stats.mtimeMs
Added in: v8.1.0
Type:


The timestamp indicating the last time this file was modified expressed in
milliseconds since the POSIX Epoch.
stats.ctimeMs
Added in: v8.1.0
Type:


The timestamp indicating the last time the file status was changed expressed
in milliseconds since the POSIX Epoch.
stats.birthtimeMs
Added in: v8.1.0
Type:


The timestamp indicating the creation time of this file expressed in
milliseconds since the POSIX Epoch.
stats.atimeNs
Added in: v12.10.0
Type:

Only present when
bigint: true
is passed into the method that generates
the object.
The timestamp indicating the last time this file was accessed expressed in
nanoseconds since the POSIX Epoch.
stats.mtimeNs
Added in: v12.10.0
Type:

Only present when
bigint: true
is passed into the method that generates
the object.
The timestamp indicating the last time this file was modified expressed in
nanoseconds since the POSIX Epoch.
stats.ctimeNs
Added in: v12.10.0
Type:

Only present when
bigint: true
is passed into the method that generates
the object.
The timestamp indicating the last time the file status was changed expressed
in nanoseconds since the POSIX Epoch.
stats.birthtimeNs
Added in: v12.10.0
Type:

Only present when
bigint: true
is passed into the method that generates
the object.
The timestamp indicating the creation time of this file expressed in
nanoseconds since the POSIX Epoch.
stats.atime
Added in: v0.11.13
Type:

The timestamp indicating the last time this file was accessed.
stats.mtime
Added in: v0.11.13
Type:

The timestamp indicating the last time this file was modified.
stats.ctime
Added in: v0.11.13
Type:

The timestamp indicating the last time the file status was changed.
stats.birthtime
Added in: v0.11.13
Type:

The timestamp indicating the creation time of this file.
Stat time values
The
atimeMs
mtimeMs
ctimeMs
birthtimeMs
properties are
numeric values that hold the corresponding times in milliseconds. Their
precision is platform specific. When
bigint: true
is passed into the
method that generates the object, the properties will be
bigints
otherwise they will be
numbers
The
atimeNs
mtimeNs
ctimeNs
birthtimeNs
properties are
bigints
that hold the corresponding times in nanoseconds. They are
only present when
bigint: true
is passed into the method that generates
the object. Their precision is platform specific.
atime
mtime
ctime
, and
birthtime
are
Date
object alternate representations of the various times. The
Date
and number values are not connected. Assigning a new number value, or
mutating the
Date
value, will not be reflected in the corresponding alternate
representation.
The times in the stat object have the following semantics:
atime
"Access Time": Time when file data last accessed. Changed
by the
mknod(2)
utimes(2)
, and
read(2)
system calls.
mtime
"Modified Time": Time when file data last modified.
Changed by the
mknod(2)
utimes(2)
, and
write(2)
system calls.
ctime
"Change Time": Time when file status was last changed
(inode data modification). Changed by the
chmod(2)
chown(2)
link(2)
mknod(2)
rename(2)
unlink(2)
utimes(2)
read(2)
, and
write(2)
system calls.
birthtime
"Birth Time": Time of file creation. Set once when the
file is created. On file systems where birthtime is not available,
this field may instead hold either the
ctime
or
1970-01-01T00:00Z
(ie, Unix epoch timestamp
). This value may be greater
than
atime
or
mtime
in this case. On Darwin and other FreeBSD variants,
also set if the
atime
is explicitly set to an earlier value than the current
birthtime
using the
utimes(2)
system call.
Prior to Node.js 0.12, the
ctime
held the
birthtime
on Windows systems. As
of 0.12,
ctime
is not "creation time", and on Unix systems, it never was.
Class:
fs.StatFs
Added in: v19.6.0, v18.15.0
Provides information about a mounted file system.
Objects returned from
fs.statfs()
and its synchronous counterpart are of
this type. If
bigint
in the
options
passed to those methods is
true
, the
numeric values will be
bigint
instead of
number
StatFs {
type: 1397114950,
bsize: 4096,
blocks: 121938943,
bfree: 61058895,
bavail: 61058895,
files: 999,
ffree: 1000000
bigint
version:
StatFs {
type: 1397114950n,
bsize: 4096n,
blocks: 121938943n,
bfree: 61058895n,
bavail: 61058895n,
files: 999n,
ffree: 1000000n
statfs.bavail
Added in: v19.6.0, v18.15.0
Type:


Free blocks available to unprivileged users.
statfs.bfree
Added in: v19.6.0, v18.15.0
Type:


Free blocks in file system.
statfs.blocks
Added in: v19.6.0, v18.15.0
Type:


Total data blocks in file system.
statfs.bsize
Added in: v19.6.0, v18.15.0
Type:


Optimal transfer block size.
statfs.ffree
Added in: v19.6.0, v18.15.0
Type:


Free file nodes in file system.
statfs.files
Added in: v19.6.0, v18.15.0
Type:


Total file nodes in file system.
statfs.type
Added in: v19.6.0, v18.15.0
Type:


Type of file system.
Class:
fs.Utf8Stream
Added in: v24.6.0
Stability: 1 - Experimental
An optimized UTF-8 stream writer that allows for flushing all the internal
buffering on demand. It handles
EAGAIN
errors correctly, allowing for
customization, for example, by dropping content if the disk is busy.
Event:
'close'
The
'close'
event is emitted when the stream is fully closed.
Event:
'drain'
The
'drain'
event is emitted when the internal buffer has drained sufficiently
to allow continued writing.
Event:
'drop'
The
'drop'
event is emitted when the maximal length is reached and that data
will not be written. The data that was dropped is passed as the first argument
to the event handler.
Event:
'error'
The
'error'
event is emitted when an error occurs.
Event:
'finish'
The
'finish'
event is emitted when the stream has been ended and all data has
been flushed to the underlying file.
Event:
'ready'
The
'ready'
event is emitted when the stream is ready to accept writes.
Event:
'write'
The
'write'
event is emitted when a write operation has completed. The number
of bytes written is passed as the first argument to the event handler.
new fs.Utf8Stream([options])
options

append

Appends writes to dest file instead of truncating it.
Default
true
contentMode

Which type of data you can send to the write
function, supported values are
'utf8'
or
'buffer'
Default
'utf8'
dest

A path to a file to be written to (mode controlled by the
append option).
fd

A file descriptor, something that is returned by
fs.open()
or
fs.openSync()
fs

An object that has the same API as the
fs
module, useful
for mocking, testing, or customizing the behavior of the stream.
fsync

Perform a
fs.fsyncSync()
every time a write is
completed.
maxLength

The maximum length of the internal buffer. If a write
operation would cause the buffer to exceed
maxLength
, the data written is
dropped and a drop event is emitted with the dropped data
maxWrite

The maximum number of bytes that can be written;
Default
16384
minLength

The minimum length of the internal buffer that is
required to be full before flushing.
mkdir

Ensure directory for
dest
file exists when true.
Default
false
mode


Specify the creating file mode (see
fs.open()
).
periodicFlush

Calls flush every
periodicFlush
milliseconds.
retryEAGAIN

A function that will be called when
write()
writeSync()
, or
flushSync()
encounters an
EAGAIN
or
EBUSY
error.
If the return value is
true
the operation will be retried, otherwise it
will bubble the error. The
err
is the error that caused this function to
be called,
writeBufferLen
is the length of the buffer that was written,
and
remainingBufferLen
is the length of the remaining buffer that the
stream did not try to write.
err

An error or
null
writeBufferLen

remainingBufferLen

sync

Perform writes synchronously.
utf8Stream.append

Whether the stream is appending to the file or truncating it.
utf8Stream.contentMode

The type of data that can be written to the stream. Supported
values are
'utf8'
or
'buffer'
Default
'utf8'
utf8Stream.destroy()
Close the stream immediately, without flushing the internal buffer.
utf8Stream.end()
Close the stream gracefully, flushing the internal buffer before closing.
utf8Stream.fd

The file descriptor that is being written to.
utf8Stream.file

The file that is being written to.
utf8Stream.flush(callback)
callback

err


An error if the flush failed, otherwise
null
Writes the current buffer to the file if a write was not in progress. Do
nothing if
minLength
is zero or if it is already writing.
utf8Stream.flushSync()
Flushes the buffered data synchronously. This is a costly operation.
utf8Stream.fsync

Whether the stream is performing a
fs.fsyncSync()
after every
write operation.
utf8Stream.maxLength

The maximum length of the internal buffer. If a write
operation would cause the buffer to exceed
maxLength
, the data written is
dropped and a drop event is emitted with the dropped data.
utf8Stream.minLength

The minimum length of the internal buffer that is required to be
full before flushing.
utf8Stream.mkdir

Whether the stream should ensure that the directory for the
dest
file exists. If
true
, it will create the directory if it does not
exist.
Default
false
utf8Stream.mode


The mode of the file that is being written to.
utf8Stream.periodicFlush

The number of milliseconds between flushes. If set to
, no
periodic flushes will be performed.
utf8Stream.reopen(file)
file



A path to a file to be written to (mode
controlled by the append option).
Reopen the file in place, useful for log rotation.
utf8Stream.sync

Whether the stream is writing synchronously or asynchronously.
utf8Stream.write(data)
data


The data to write.
Returns

When the
options.contentMode
is set to
'utf8'
when the stream is created,
the
data
argument must be a string. If the
contentMode
is set to
'buffer'
the
data
argument must be a

utf8Stream.writing

Whether the stream is currently writing data to the file.
utf8Stream[Symbol.dispose]()
Calls
utf8Stream.destroy()
Class:
fs.WriteStream
Added in: v0.1.93
Extends

Instances of

cannot be constructed directly. They are created and
returned using the
fs.createWriteStream()
function.
Event:
'close'
Added in: v0.1.93
Emitted when the

's underlying file descriptor has been closed.
Event:
'open'
Added in: v0.1.93
fd

Integer file descriptor used by the

Emitted when the

's file is opened.
Event:
'ready'
Added in: v9.11.0
Emitted when the

is ready to be used.
Fires immediately after
'open'
writeStream.bytesWritten
Added in: v0.4.7
The number of bytes written so far. Does not include data that is still queued
for writing.
writeStream.close([callback])
Added in: v0.9.4
callback

err

Closes
writeStream
. Optionally accepts a
callback that will be executed once the
writeStream
is closed.
writeStream.path
Added in: v0.1.93
The path to the file the stream is writing to as specified in the first
argument to
fs.createWriteStream()
. If
path
is passed as a string, then
writeStream.path
will be a string. If
path
is passed as a

, then
writeStream.path
will be a

writeStream.pending
Added in: v11.2.0
Type:

This property is
true
if the underlying file has not been opened yet,
i.e. before the
'ready'
event is emitted.
fs.constants
Type:

Returns an object containing commonly used constants for file system
operations.
FS constants
The following constants are exported by
fs.constants
and
fsPromises.constants
Not every constant will be available on every operating system;
this is especially important for Windows, where many of the POSIX specific
definitions are not available.
For portable applications it is recommended to check for their presence
before use.
To use more than one constant, use the bitwise OR
operator.
Example:
import
open
constants
from
'node:fs'
const
O_RDWR
O_CREAT
O_EXCL
constants
open
'/path/to/my/file'
O_RDWR
O_CREAT
O_EXCL
err
fd
=>
// ...
File access constants
The following constants are meant for use as the
mode
parameter passed to
fsPromises.access()
fs.access()
, and
fs.accessSync()
Constant
Description
F_OK
Flag indicating that the file is visible to the calling process.
This is useful for determining if a file exists, but says nothing
about
rwx
permissions. Default if no mode is specified.
R_OK
Flag indicating that the file can be read by the calling process.
W_OK
Flag indicating that the file can be written by the calling
process.
X_OK
Flag indicating that the file can be executed by the calling
process. This has no effect on Windows
(will behave like
fs.constants.F_OK
).
The definitions are also available on Windows.
File copy constants
The following constants are meant for use with
fs.copyFile()
Constant
Description
COPYFILE_EXCL
If present, the copy operation will fail with an error if the
destination path already exists.
COPYFILE_FICLONE
If present, the copy operation will attempt to create a
copy-on-write reflink. If the underlying platform does not support
copy-on-write, then a fallback copy mechanism is used.
COPYFILE_FICLONE_FORCE
If present, the copy operation will attempt to create a
copy-on-write reflink. If the underlying platform does not support
copy-on-write, then the operation will fail with an error.
The definitions are also available on Windows.
File open constants
The following constants are meant for use with
fs.open()
Constant
Description
O_RDONLY
Flag indicating to open a file for read-only access.
O_WRONLY
Flag indicating to open a file for write-only access.
O_RDWR
Flag indicating to open a file for read-write access.
O_CREAT
Flag indicating to create the file if it does not already exist.
O_EXCL
Flag indicating that opening a file should fail if the
O_CREAT
flag is set and the file already exists.
O_NOCTTY
Flag indicating that if path identifies a terminal device, opening the
path shall not cause that terminal to become the controlling terminal for
the process (if the process does not already have one).
O_TRUNC
Flag indicating that if the file exists and is a regular file, and the
file is opened successfully for write access, its length shall be truncated
to zero.
O_APPEND
Flag indicating that data will be appended to the end of the file.
O_DIRECTORY
Flag indicating that the open should fail if the path is not a
directory.
O_NOATIME
Flag indicating reading accesses to the file system will no longer
result in an update to the
atime
information associated with
the file. This flag is available on Linux operating systems only.
O_NOFOLLOW
Flag indicating that the open should fail if the path is a symbolic
link.
O_SYNC
Flag indicating that the file is opened for synchronized I/O with write
operations waiting for file integrity.
O_DSYNC
Flag indicating that the file is opened for synchronized I/O with write
operations waiting for data integrity.
O_SYMLINK
Flag indicating to open the symbolic link itself rather than the
resource it is pointing to.
O_DIRECT
When set, an attempt will be made to minimize caching effects of file
I/O.
O_NONBLOCK
Flag indicating to open the file in nonblocking mode when possible.
UV_FS_O_FILEMAP
When set, a memory file mapping is used to access the file. This flag
is available on Windows operating systems only. On other operating systems,
this flag is ignored.
On Windows, only
O_APPEND
O_CREAT
O_EXCL
O_RDONLY
O_RDWR
O_TRUNC
O_WRONLY
, and
UV_FS_O_FILEMAP
are available.
File type constants
The following constants are meant for use with the

object's
mode
property for determining a file's type.
Constant
Description
S_IFMT
Bit mask used to extract the file type code.
S_IFREG
File type constant for a regular file.
S_IFDIR
File type constant for a directory.
S_IFCHR
File type constant for a character-oriented device file.
S_IFBLK
File type constant for a block-oriented device file.
S_IFIFO
File type constant for a FIFO/pipe.
S_IFLNK
File type constant for a symbolic link.
S_IFSOCK
File type constant for a socket.
On Windows, only
S_IFCHR
S_IFDIR
S_IFLNK
S_IFMT
, and
S_IFREG
are available.
File mode constants
The following constants are meant for use with the

object's
mode
property for determining the access permissions for a file.
Constant
Description
S_IRWXU
File mode indicating readable, writable, and executable by owner.
S_IRUSR
File mode indicating readable by owner.
S_IWUSR
File mode indicating writable by owner.
S_IXUSR
File mode indicating executable by owner.
S_IRWXG
File mode indicating readable, writable, and executable by group.
S_IRGRP
File mode indicating readable by group.
S_IWGRP
File mode indicating writable by group.
S_IXGRP
File mode indicating executable by group.
S_IRWXO
File mode indicating readable, writable, and executable by others.
S_IROTH
File mode indicating readable by others.
S_IWOTH
File mode indicating writable by others.
S_IXOTH
File mode indicating executable by others.
On Windows, only
S_IRUSR
and
S_IWUSR
are available.
Notes
Ordering of callback and promise-based operations
Because they are executed asynchronously by the underlying thread pool,
there is no guaranteed ordering when using either the callback or
promise-based methods.
For example, the following is prone to error because the
fs.stat()
operation might complete before the
fs.rename()
operation:
const
fs
require
'node:fs'
fs
rename
'/tmp/hello'
'/tmp/world'
err
=>
if
(err)
throw
err
console
log
'renamed complete'
fs
stat
'/tmp/world'
err
stats
=>
if
(err)
throw
err
console
log
`stats:
${
JSON
stringify
stats
It is important to correctly order the operations by awaiting the results
of one before invoking the other:
import
rename
stat
from
'node:fs/promises'
const
oldPath
'/tmp/hello'
const
newPath
'/tmp/world'
try
await
rename
(oldPath
newPath)
const
stats
await
stat
(newPath)
console
log
`stats:
${
JSON
stringify
stats
catch
(error)
console
error
'there was an error:'
error
message)
const
rename
stat
require
'node:fs/promises'
async
function
oldPath
newPath
try
await
rename
(oldPath
newPath)
const
stats
await
stat
(newPath)
console
log
`stats:
${
JSON
stringify
stats
catch
(error)
console
error
'there was an error:'
error
message)
)(
'/tmp/hello'
'/tmp/world'
Or, when using the callback APIs, move the
fs.stat()
call into the callback
of the
fs.rename()
operation:
import
rename
stat
from
'node:fs'
rename
'/tmp/hello'
'/tmp/world'
err
=>
if
(err)
throw
err
stat
'/tmp/world'
err
stats
=>
if
(err)
throw
err
console
log
`stats:
${
JSON
stringify
stats
const
rename
stat
require
'node:fs/promises'
rename
'/tmp/hello'
'/tmp/world'
err
=>
if
(err)
throw
err
stat
'/tmp/world'
err
stats
=>
if
(err)
throw
err
console
log
`stats:
${
JSON
stringify
stats
File paths
Most
fs
operations accept file paths that may be specified in the form of
a string, a

, or a

object using the
file:
protocol.
String paths
String paths are interpreted as UTF-8 character sequences identifying
the absolute or relative filename. Relative paths will be resolved relative
to the current working directory as determined by calling
process.cwd()
Example using an absolute path on POSIX:
import
open
from
'node:fs/promises'
let
fd
try
fd
await
open
'/open/some/file.txt'
'r'
// Do something with the file
finally
await
fd
?.
close
()
Example using a relative path on POSIX (relative to
process.cwd()
):
import
open
from
'node:fs/promises'
let
fd
try
fd
await
open
'file.txt'
'r'
// Do something with the file
finally
await
fd
?.
close
()
File URL paths
Added in: v7.6.0
For most
node:fs
module functions, the
path
or
filename
argument may be
passed as a

object using the
file:
protocol.
import
readFileSync
from
'node:fs'
readFileSync
new
URL
'file:///tmp/hello'
))
file:
URLs are always absolute paths.
Platform-specific considerations
On Windows,
file:

s with a host name convert to UNC paths, while
file:

s with drive letters convert to local absolute paths.
file:

with no host name and no drive letter will result in an error:
import
readFileSync
from
'node:fs'
// On Windows :
// - WHATWG file URLs with hostname convert to UNC path
// file://hostname/p/a/t/h/file => \\hostname\p\a\t\h\file
readFileSync
new
URL
'file://hostname/p/a/t/h/file'
))
// - WHATWG file URLs with drive letters convert to absolute path
// file:///C:/tmp/hello => C:\tmp\hello
readFileSync
new
URL
'file:///C:/tmp/hello'
))
// - WHATWG file URLs without hostname must have a drive letters
readFileSync
new
URL
'file:///notdriveletter/p/a/t/h/file'
))
readFileSync
new
URL
'file:///c/p/a/t/h/file'
))
// TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must be absolute
file:

s with drive letters must use
as a separator just after
the drive letter. Using another separator will result in an error.
On all other platforms,
file:

s with a host name are unsupported and
will result in an error:
import
readFileSync
from
'node:fs'
// On other platforms:
// - WHATWG file URLs with hostname are unsupported
// file://hostname/p/a/t/h/file => throw!
readFileSync
new
URL
'file://hostname/p/a/t/h/file'
))
// TypeError [ERR_INVALID_FILE_URL_PATH]: must be absolute
// - WHATWG file URLs convert to absolute path
// file:///tmp/hello => /tmp/hello
readFileSync
new
URL
'file:///tmp/hello'
))
file:

having encoded slash characters will result in an error on all
platforms:
import
readFileSync
from
'node:fs'
// On Windows
readFileSync
new
URL
'file:///C:/p/a/t/h/%2F'
))
readFileSync
new
URL
'file:///C:/p/a/t/h/%2f'
))
/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded
\ or / characters */
// On POSIX
readFileSync
new
URL
'file:///p/a/t/h/%2F'
))
readFileSync
new
URL
'file:///p/a/t/h/%2f'
))
/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded
/ characters */
On Windows,
file:

s having encoded backslash will result in an error:
import
readFileSync
from
'node:fs'
// On Windows
readFileSync
new
URL
'file:///C:/path/%5C'
))
readFileSync
new
URL
'file:///C:/path/%5c'
))
/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded
\ or / characters */
Buffer paths
Paths specified using a

are useful primarily on certain POSIX
operating systems that treat file paths as opaque byte sequences. On such
systems, it is possible for a single file path to contain sub-sequences that
use multiple character encodings. As with string paths,

paths may
be relative or absolute:
Example using an absolute path on POSIX:
import
open
from
'node:fs/promises'
import
Buffer
from
'node:buffer'
let
fd
try
fd
await
open
(Buffer
from
'/open/some/file.txt'
'r'
// Do something with the file
finally
await
fd
?.
close
()
Per-drive working directories on Windows
On Windows, Node.js follows the concept of per-drive working directory. This
behavior can be observed when using a drive path without a backslash. For
example
fs.readdirSync('C:\\')
can potentially return a different result than
fs.readdirSync('C:')
. For more information, see
this MSDN page
File descriptors
On POSIX systems, for every process, the kernel maintains a table of currently
open files and resources. Each open file is assigned a simple numeric
identifier called a
file descriptor
. At the system-level, all file system
operations use these file descriptors to identify and track each specific
file. Windows systems use a different but conceptually similar mechanism for
tracking resources. To simplify things for users, Node.js abstracts away the
differences between operating systems and assigns all open files a numeric file
descriptor.
The callback-based
fs.open()
, and synchronous
fs.openSync()
methods open a
file and allocate a new file descriptor. Once allocated, the file descriptor may
be used to read data from, write data to, or request information about the file.
Operating systems limit the number of file descriptors that may be open
at any given time so it is critical to close the descriptor when operations
are completed. Failure to do so will result in a memory leak that will
eventually cause an application to crash.
import
open
close
fstat
from
'node:fs'
function
closeFd
fd
close
(fd
err
=>
if
(err)
throw
err
open
'/open/some/file.txt'
'r'
err
fd
=>
if
(err)
throw
err
try
fstat
(fd
err
stat
=>
if
(err)
closeFd
(fd)
throw
err
// use stat
closeFd
(fd)
catch
(err)
closeFd
(fd)
throw
err
The promise-based APIs use a

object in place of the numeric
file descriptor. These objects are better managed by the system to ensure
that resources are not leaked. However, it is still required that they are
closed when operations are completed:
import
open
from
'node:fs/promises'
let
file
try
file
await
open
'/open/some/file.txt'
'r'
const
stat
await
file
stat
()
// use stat
finally
await
file
close
()
Threadpool usage
All callback and promise-based file system APIs (with the exception of
fs.FSWatcher()
) use libuv's threadpool. This can have surprising and negative
performance implications for some applications. See the
UV_THREADPOOL_SIZE
documentation for more information.
File system flags
The following flags are available wherever the
flag
option takes a
string.
'a'
: Open file for appending.
The file is created if it does not exist.
'ax'
: Like
'a'
but fails if the path exists.
'a+'
: Open file for reading and appending.
The file is created if it does not exist.
'ax+'
: Like
'a+'
but fails if the path exists.
'as'
: Open file for appending in synchronous mode.
The file is created if it does not exist.
'as+'
: Open file for reading and appending in synchronous mode.
The file is created if it does not exist.
'r'
: Open file for reading.
An exception occurs if the file does not exist.
'rs'
: Open file for reading in synchronous mode.
An exception occurs if the file does not exist.
'r+'
: Open file for reading and writing.
An exception occurs if the file does not exist.
'rs+'
: Open file for reading and writing in synchronous mode. Instructs
the operating system to bypass the local file system cache.
This is primarily useful for opening files on NFS mounts as it allows
skipping the potentially stale local cache. It has a very real impact on
I/O performance so using this flag is not recommended unless it is needed.
This doesn't turn
fs.open()
or
fsPromises.open()
into a synchronous
blocking call. If synchronous operation is desired, something like
fs.openSync()
should be used.
'w'
: Open file for writing.
The file is created (if it does not exist) or truncated (if it exists).
'wx'
: Like
'w'
but fails if the path exists.
'w+'
: Open file for reading and writing.
The file is created (if it does not exist) or truncated (if it exists).
'wx+'
: Like
'w+'
but fails if the path exists.
flag
can also be a number as documented by
open(2)
; commonly used constants
are available from
fs.constants
. On Windows, flags are translated to
their equivalent ones where applicable, e.g.
O_WRONLY
to
FILE_GENERIC_WRITE
or
O_EXCL|O_CREAT
to
CREATE_NEW
, as accepted by
CreateFileW
The exclusive flag
'x'
O_EXCL
flag in
open(2)
) causes the operation to
return an error if the path already exists. On POSIX, if the path is a symbolic
link, using
O_EXCL
returns an error even if the link is to a path that does
not exist. The exclusive flag might not work with network file systems.
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.
Modifying a file rather than replacing it may require the
flag
option to be
set to
'r+'
rather than the default
'w'
The behavior of some flags are platform-specific. As such, opening a directory
on macOS and Linux with the
'a+'
flag, as in the example below, will return an
error. In contrast, on Windows and FreeBSD, a file descriptor or a
FileHandle
will be returned.
// macOS and Linux
fs
open
''
'a+'
err
fd
=>
// => [Error: EISDIR: illegal operation on a directory, open ]
// Windows and FreeBSD
fs
open
''
'a+'
err
fd
=>
// => null,
On Windows, opening an existing hidden file using the
'w'
flag (either
through
fs.open()
fs.writeFile()
, or
fsPromises.open()
) will fail with
EPERM
. Existing hidden files can be opened for writing with the
'r+'
flag.
A call to
fs.ftruncate()
or
filehandle.truncate()
can be used to reset
the file contents.

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