Interface FileHandle

Readonly fd

[asyncDispose]

• [asyncDispose](): Promise<void>

• An alias for ().

  Returns Promise<void>

  Since

  v18.18.0

appendFile

• appendFile(data, options?): Promise<void>

• Alias of filehandle.writeFile().

  When operating on file handles, the mode cannot be changed from what it was set to with fsPromises.open(). Therefore, this is equivalent to filehandle.writeFile().

  Parameters

  • data: string | Uint8Array

  • Optional options: BufferEncoding | ObjectEncodingOptions & FlagAndOpenMode

  Returns Promise<void>

  Fulfills with undefined upon success.

  Since

  v10.0.0

chmod

• chmod(mode): Promise<void>

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

  Parameters

  • mode: Mode

    the file mode bit mask.

  Returns Promise<void>

  Fulfills with undefined upon success.

  Since

  v10.0.0

chown

• chown(uid, gid): Promise<void>

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

  Parameters

  • uid: number

    The file's new owner's user id.

  • gid: number

    The file's new group's group id.

  Returns Promise<void>

  Fulfills with undefined upon success.

  Since

  v10.0.0

close

• close(): Promise<void>

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

  import { open } from 'fs/promises';
  
  let filehandle;
  try {
    filehandle = await open('thefile.txt', 'r');
  } finally {
    await filehandle?.close();
  }
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  Returns Promise<void>

  Fulfills with undefined upon success.

  Since

  v10.0.0

createReadStream

• createReadStream(options?): ReadStream

• Unlike the 16 kb default highWaterMark for a stream.Readable, the stream returned by this method has a default highWaterMark of 64 kb.

  options can include start and end values to read a range of bytes from the file instead of the entire file. Both start and end are inclusive and start counting at 0, allowed values are in the [0, Number.MAX_SAFE_INTEGER] range. If start is omitted or undefined, filehandle.createReadStream() reads sequentially from the current file position. The encoding can be any one of those accepted by Buffer.

  If the FileHandle points to a character device that only supports blocking reads (such as keyboard or sound card), read operations do not finish until data is available. This can prevent the process from exiting and the stream from closing naturally.

  By default, the stream will emit a 'close' event after it has been destroyed. Set the emitClose option to false to change this behavior.

  import { open } from 'fs/promises';
  
  const fd = await open('/dev/input/event0');
  // Create a stream from some character device.
  const stream = fd.createReadStream();
  setTimeout(() => {
    stream.close(); // This may not close the stream.
    // Artificially marking end-of-stream, as if the underlying resource had
    // indicated end-of-file by itself, allows the stream to close.
    // This does not cancel pending read operations, and if there is such an
    // operation, the process may still not be able to exit successfully
    // until it finishes.
    stream.push(null);
    stream.read(0);
  }, 100);
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  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 'fs/promises';
  
  const fd = await open('sample.txt');
  fd.createReadStream({ start: 90, end: 99 });
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  Parameters

  • Optional options: CreateReadStreamOptions

  Returns ReadStream

  Since

  v16.11.0

createWriteStream

• createWriteStream(options?): WriteStream

• options may also include a start option to allow writing data at some position past the beginning of the file, allowed values are in the [0, Number.MAX_SAFE_INTEGER] range. Modifying a file rather than replacing it may require the flags open option to be set to r+ rather than the default r. The encoding can be any one of those accepted by Buffer.

  If autoClose is set to true (default behavior) on 'error' or 'finish'the file descriptor will be closed automatically. If autoClose is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak.

  By default, the stream will emit a 'close' event after it has been destroyed. Set the emitClose option to false to change this behavior.

  Parameters

  • Optional options: CreateWriteStreamOptions

  Returns WriteStream

  Since

  v16.11.0

datasync

• datasync(): Promise<void>

• Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX fdatasync(2) documentation for details.

  Unlike filehandle.sync this method does not flush modified metadata.

  Returns Promise<void>

  Fulfills with undefined upon success.

  Since

  v10.0.0

read

• read<T>(buffer, offset?, length?, position?): Promise<FileReadResult<T>>

• Reads data from the file and stores that in the given buffer.

  If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero.

  Type Parameters

  • T extends ArrayBufferView

  Parameters

  • buffer: T

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

  • Optional offset: number

    The location in the buffer at which to start filling.

  • Optional length: number

    The number of bytes to read.

  • Optional position: number

    The location where to begin reading data from the file. If null, data will be read from the current file position, and the position will be updated. If position is an integer, the current file position will remain unchanged.

  Returns Promise<FileReadResult<T>>

  Fulfills upon success with an object with two properties:

  Since

  v10.0.0

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

• Type Parameters

  • T extends ArrayBufferView = Buffer

  Parameters

  • Optional options: FileReadOptions<T>

  Returns Promise<FileReadResult<T>>

readFile

• readFile(options?): Promise<Buffer>

• Asynchronously reads the entire contents of a file.

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

  The FileHandle has to support reading.

  If one or more filehandle.read() calls are made on a file handle and then afilehandle.readFile() call is made, the data will be read from the current position till the end of the file. It doesn't always read from the beginning of the file.

  Parameters

  • Optional options: {
        encoding?: null;
        flag?: OpenMode;
    }

    • Optional encoding?: null

    • Optional flag?: OpenMode

  Returns Promise<Buffer>

  Fulfills upon a successful read with the contents of the file. If no encoding is specified (using options.encoding), the data is returned as a {Buffer} object. Otherwise, the data will be a string.

  Since

  v10.0.0

• readFile(options): Promise<string>

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

  Parameters

  • options: BufferEncoding | {
        encoding: BufferEncoding;
        flag?: OpenMode;
    }

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

  Returns Promise<string>
• readFile(options?): Promise<string | Buffer>

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

  Parameters

  • Optional options: BufferEncoding | ObjectEncodingOptions & {
        flag?: OpenMode;
    }

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

  Returns Promise<string | Buffer>

readLines

• readLines(options?): Interface

• Convenience method to create a readline interface and stream over the file. For example:

  import { open } from 'node:fs/promises';
  
  const file = await open('./some/file/to/read');
  
  for await (const line of file.readLines()) {
    console.log(line);
  }
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  Parameters

  • Optional options: CreateReadStreamOptions

    See filehandle.createReadStream() for the options.

  Returns Interface

  Since

  v18.11.0

readableWebStream

• readableWebStream(options?): ReadableStream<any>
• Experimental

  Returns a ReadableStream that may be used to read the files data.

  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();
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  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.

  Parameters

  • Optional options: ReadableWebStreamOptions

  Returns ReadableStream<any>

  Since

  v17.0.0

readv

• readv(buffers, position?): Promise<ReadVResult>

• Read from a file and write to an array of ArrayBufferView s

  Parameters

  • buffers: readonly ArrayBufferView[]

  • Optional position: number

    The offset from the beginning of the file where the data should be read from. If position is not a number, the data will be read from the current position.

  Returns Promise<ReadVResult>

  Fulfills upon success an object containing two properties:

  Since

  v13.13.0, v12.17.0

stat

• stat(opts?): Promise<Stats>

• Parameters

  • Optional opts: StatOptions & {
        bigint?: false;
    }

  Returns Promise<Stats>

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

  Since

  v10.0.0

• stat(opts): Promise<BigIntStats>

• Parameters

  • opts: StatOptions & {
        bigint: true;
    }

  Returns Promise<BigIntStats>

• stat(opts?): Promise<Stats | BigIntStats>

• Parameters

  • Optional opts: StatOptions

  Returns Promise<Stats | BigIntStats>

sync

• sync(): Promise<void>

• Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX fsync(2) documentation for more detail.

  Returns Promise<void>

  Fufills with undefined upon success.

  Since

  v10.0.0

truncate

• truncate(len?): Promise<void>

• Truncates the file.

  If the file was larger than len bytes, only the first len bytes will be retained in the file.

  The following example retains only the first four bytes of the file:

  import { open } from 'fs/promises';
  
  let filehandle = null;
  try {
    filehandle = await open('temp.txt', 'r+');
    await filehandle.truncate(4);
  } finally {
    await filehandle?.close();
  }
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  If the file previously was shorter than len bytes, it is extended, and the extended part is filled with null bytes ('\0'):

  If len is negative then 0 will be used.

  Parameters

  • Optional len: number

  Returns Promise<void>

  Fulfills with undefined upon success.

  Since

  v10.0.0

utimes

• utimes(atime, mtime): Promise<void>

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

  Parameters

  • atime: TimeLike

  • mtime: TimeLike

  Returns Promise<void>

  Since

  v10.0.0

write

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

• Write buffer to the file.

  The promise is resolved with an object containing two properties:

  It is unsafe to use filehandle.write() multiple times on the same file without waiting for the promise to be resolved (or rejected). For this scenario, use filehandle.createWriteStream().

  On Linux, positional writes do not work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.

  Type Parameters

  • TBuffer extends Uint8Array

  Parameters

  • buffer: TBuffer

  • Optional offset: number

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

  • Optional length: number

  • Optional position: number

    The offset from the beginning of the file where the data from buffer should be written. If position is not a number, the data will be written at the current position. See the POSIX pwrite(2) documentation for more detail.

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

  Since

  v10.0.0

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

• Parameters

  • data: string

  • Optional position: number

  • Optional encoding: BufferEncoding

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

writeFile

• writeFile(data, options?): Promise<void>

• Asynchronously writes data to a file, replacing the file if it already exists.data can be a string, a buffer, an AsyncIterable or Iterable object. The promise is resolved with no arguments upon success.

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

  The FileHandle has to support writing.

  It is unsafe to use filehandle.writeFile() multiple times on the same file without waiting for the promise to be resolved (or rejected).

  If one or more filehandle.write() calls are made on a file handle and then afilehandle.writeFile() call is made, the data will be written from the current position till the end of the file. It doesn't always write from the beginning of the file.

  Parameters

  • data: string | Uint8Array

  • Optional options: BufferEncoding | ObjectEncodingOptions & FlagAndOpenMode & Abortable

  Returns Promise<void>

  Since

  v10.0.0

writev

• writev(buffers, position?): Promise<WriteVResult>

• Write an array of ArrayBufferView s to the file.

  The promise is resolved with an object containing a two properties:

  It is unsafe to call writev() multiple times on the same file without waiting for the promise to be resolved (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.

  Parameters

  • buffers: readonly ArrayBufferView[]

  • Optional position: number

    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.

  Returns Promise<WriteVResult>

  Since

  v12.9.0