type

Referenced types

class ArrayBuffer

Represents a raw buffer of binary data, which is used to store data for the different typed arrays. ArrayBuffers cannot be read from or written to directly, but can be passed to a typed array or DataView Object to interpret the raw buffer as needed.

readonly [Symbol.toStringTag]: string
readonly byteLength: number
Read-only. The length of the ArrayBuffer (in bytes).
resize(
newByteLength?: number
): void;
Resizes the ArrayBuffer to the specified size (in bytes).
MDN
resize(
byteLength: number
): ArrayBuffer;
Resize an ArrayBuffer in-place.
slice(
begin: number,
end?: number
): ArrayBuffer;
Returns a section of an ArrayBuffer.
transfer(
newByteLength?: number
): ArrayBuffer;
Creates a new ArrayBuffer with the same byte content as this buffer, then detaches this buffer.
MDN
transferToFixedLength(
newByteLength?: number
): ArrayBuffer;
Creates a new non-resizable ArrayBuffer with the same byte content as this buffer, then detaches this buffer.
MDN

interface MessagePort

The NodeEventTarget is a Node.js-specific extension to EventTarget that emulates a subset of the EventEmitter API.

onclose: null | (ev: Event) => void
onmessage: null | (ev: MessageEvent<any>) => void
onmessageerror: null | (ev: MessageEvent<any>) => void
addEventListener<K extends keyof MessagePortEventMap>(
type: K,
listener: (ev: MessagePortEventMap[K]) => void,
options?: boolean | AddEventListenerOptions
): void;
Appends an event listener for events whose type attribute value is type. The callback argument sets the callback that will be invoked when the event is dispatched.
The options argument sets listener-specific options. For compatibility this can be a boolean, in which case the method behaves exactly as if the value was specified as options's capture.
When set to true, options's capture prevents callback from being invoked when the event's eventPhase attribute value is BUBBLING_PHASE. When false (or not present), callback will not be invoked when event's eventPhase attribute value is CAPTURING_PHASE. Either way, callback will be invoked if event's eventPhase attribute value is AT_TARGET.
When set to true, options's passive indicates that the callback will not cancel the event by invoking preventDefault(). This is used to enable performance optimizations described in § 2.8 Observing event listeners.
When set to true, options's once indicates that the callback will only be invoked once after which the event listener will be removed.
If an AbortSignal is passed for options's signal, then the event listener will be removed when signal is aborted.
The event listener is appended to target's event listener list and is not appended if it has the same type, callback, and capture.
MDN Reference
addEventListener(
type: string,
listener: EventListener | EventListenerObject,
options?: boolean | AddEventListenerOptions
): void;
Appends an event listener for events whose type attribute value is type. The callback argument sets the callback that will be invoked when the event is dispatched.
The options argument sets listener-specific options. For compatibility this can be a boolean, in which case the method behaves exactly as if the value was specified as options's capture.
When set to true, options's capture prevents callback from being invoked when the event's eventPhase attribute value is BUBBLING_PHASE. When false (or not present), callback will not be invoked when event's eventPhase attribute value is CAPTURING_PHASE. Either way, callback will be invoked if event's eventPhase attribute value is AT_TARGET.
When set to true, options's passive indicates that the callback will not cancel the event by invoking preventDefault(). This is used to enable performance optimizations described in § 2.8 Observing event listeners.
When set to true, options's once indicates that the callback will only be invoked once after which the event listener will be removed.
If an AbortSignal is passed for options's signal, then the event listener will be removed when signal is aborted.
The event listener is appended to target's event listener list and is not appended if it has the same type, callback, and capture.
MDN Reference
addListener(
event: 'close',
listener: (ev: Event) => void
): this;
Node.js-specific extension to the EventTarget class that emulates the equivalent EventEmitter API. The only difference between addListener() and addEventListener() is that addListener() will return a reference to the EventTarget.
addListener(
event: 'message',
listener: (value: any) => void
): this;
Node.js-specific extension to the EventTarget class that emulates the equivalent EventEmitter API. The only difference between addListener() and addEventListener() is that addListener() will return a reference to the EventTarget.
addListener(
event: 'messageerror',
listener: (error: Error) => void
): this;
Node.js-specific extension to the EventTarget class that emulates the equivalent EventEmitter API. The only difference between addListener() and addEventListener() is that addListener() will return a reference to the EventTarget.
addListener(
event: string,
listener: (arg: any) => void
): this;
Node.js-specific extension to the EventTarget class that emulates the equivalent EventEmitter API. The only difference between addListener() and addEventListener() is that addListener() will return a reference to the EventTarget.
close(): void;
dispatchEvent(
event: Event
): boolean;
Dispatches a synthetic event event to target and returns true if either event's cancelable attribute value is false or its preventDefault() method was not invoked, and false otherwise.
MDN Reference
emit(
event: 'close',
ev: Event
): boolean;
Node.js-specific extension to the EventTarget class that dispatches the arg to the list of handlers for type.
@returns
true if event listeners registered for the type exist, otherwise false.
emit(
event: 'message',
value: any
): boolean;
Node.js-specific extension to the EventTarget class that dispatches the arg to the list of handlers for type.
@returns
true if event listeners registered for the type exist, otherwise false.
emit(
event: 'messageerror',
error: Error
): boolean;
Node.js-specific extension to the EventTarget class that dispatches the arg to the list of handlers for type.
@returns
true if event listeners registered for the type exist, otherwise false.
emit(
event: string,
arg: any
): boolean;
Node.js-specific extension to the EventTarget class that dispatches the arg to the list of handlers for type.
@returns
true if event listeners registered for the type exist, otherwise false.
eventNames(): string[];
Node.js-specific extension to the EventTarget class that returns an array of event type names for which event listeners are registered.
getMaxListeners(): number;
Node.js-specific extension to the EventTarget class that returns the number of max event listeners.
hasRef(): boolean;
listenerCount(
type: string
): number;
Node.js-specific extension to the EventTarget class that returns the number of event listeners registered for the type.
off(
event: 'close',
listener: (ev: Event) => void,
options?: EventListenerOptions
): this;
Node.js-specific alias for eventTarget.removeEventListener().
off(
event: 'message',
listener: (value: any) => void,
options?: EventListenerOptions
): this;
Node.js-specific alias for eventTarget.removeEventListener().
off(
event: 'messageerror',
listener: (error: Error) => void,
options?: EventListenerOptions
): this;
Node.js-specific alias for eventTarget.removeEventListener().
off(
event: string,
listener: (arg: any) => void,
options?: EventListenerOptions
): this;
Node.js-specific alias for eventTarget.removeEventListener().
on(
event: 'close',
listener: (ev: Event) => void
): this;
Node.js-specific alias for eventTarget.addEventListener().
on(
event: 'message',
listener: (value: any) => void
): this;
Node.js-specific alias for eventTarget.addEventListener().
on(
event: 'messageerror',
listener: (error: Error) => void
): this;
Node.js-specific alias for eventTarget.addEventListener().
on(
event: string,
listener: (arg: any) => void
): this;
Node.js-specific alias for eventTarget.addEventListener().
once(
event: 'close',
listener: (ev: Event) => void
): this;
Node.js-specific extension to the EventTarget class that adds a once listener for the given event type. This is equivalent to calling on with the once option set to true.
once(
event: 'message',
listener: (value: any) => void
): this;
Node.js-specific extension to the EventTarget class that adds a once listener for the given event type. This is equivalent to calling on with the once option set to true.
once(
event: 'messageerror',
listener: (error: Error) => void
): this;
Node.js-specific extension to the EventTarget class that adds a once listener for the given event type. This is equivalent to calling on with the once option set to true.
once(
event: string,
listener: (arg: any) => void
): this;
Node.js-specific extension to the EventTarget class that adds a once listener for the given event type. This is equivalent to calling on with the once option set to true.
postMessage(
message: any,
transfer: Transferable[]
): void;
postMessage(
message: any,
options?: StructuredSerializeOptions
): void;
ref(): void;
removeAllListeners(
type?: string
): this;
Node.js-specific extension to the EventTarget class. If type is specified, removes all registered listeners for type, otherwise removes all registered listeners.
removeEventListener<K extends keyof MessagePortEventMap>(
type: K,
listener: (ev: MessagePortEventMap[K]) => void,
options?: boolean | EventListenerOptions
): void;
Removes the event listener in target's event listener list with the same type, callback, and options.
MDN Reference
removeEventListener(
type: string,
listener: EventListener | EventListenerObject,
options?: boolean | EventListenerOptions
): void;
Removes the event listener in target's event listener list with the same type, callback, and options.
MDN Reference
removeListener(
event: 'close',
listener: (ev: Event) => void,
options?: EventListenerOptions
): this;
Node.js-specific extension to the EventTarget class that removes the listener for the given type. The only difference between removeListener() and removeEventListener() is that removeListener() will return a reference to the EventTarget.
removeListener(
event: 'message',
listener: (value: any) => void,
options?: EventListenerOptions
): this;
Node.js-specific extension to the EventTarget class that removes the listener for the given type. The only difference between removeListener() and removeEventListener() is that removeListener() will return a reference to the EventTarget.
removeListener(
event: 'messageerror',
listener: (error: Error) => void,
options?: EventListenerOptions
): this;
Node.js-specific extension to the EventTarget class that removes the listener for the given type. The only difference between removeListener() and removeEventListener() is that removeListener() will return a reference to the EventTarget.
removeListener(
event: string,
listener: (arg: any) => void,
options?: EventListenerOptions
): this;
Node.js-specific extension to the EventTarget class that removes the listener for the given type. The only difference between removeListener() and removeEventListener() is that removeListener() will return a reference to the EventTarget.
setMaxListeners(
n: number
): void;
Node.js-specific extension to the EventTarget class that sets the number of max event listeners as n.
start(): void;
unref(): void;

class AbortSignal

A signal object that allows you to communicate with a DOM request (such as a Fetch) and abort it if required via an AbortController object.

MDN Reference

readonly aborted: boolean
Returns true if this AbortSignal's AbortController has signaled to abort, and false otherwise.
MDN Reference
onabort: null | (this: AbortSignal, ev: Event) => any
MDN Reference
readonly reason: any
MDN Reference
addEventListener<K extends 'abort'>(
type: K,
listener: (this: AbortSignal, ev: AbortSignalEventMap[K]) => any,
options?: boolean | AddEventListenerOptions
): void;
Appends an event listener for events whose type attribute value is type. The callback argument sets the callback that will be invoked when the event is dispatched.
The options argument sets listener-specific options. For compatibility this can be a boolean, in which case the method behaves exactly as if the value was specified as options's capture.
When set to true, options's capture prevents callback from being invoked when the event's eventPhase attribute value is BUBBLING_PHASE. When false (or not present), callback will not be invoked when event's eventPhase attribute value is CAPTURING_PHASE. Either way, callback will be invoked if event's eventPhase attribute value is AT_TARGET.
When set to true, options's passive indicates that the callback will not cancel the event by invoking preventDefault(). This is used to enable performance optimizations described in § 2.8 Observing event listeners.
When set to true, options's once indicates that the callback will only be invoked once after which the event listener will be removed.
If an AbortSignal is passed for options's signal, then the event listener will be removed when signal is aborted.
The event listener is appended to target's event listener list and is not appended if it has the same type, callback, and capture.
MDN Reference
dispatchEvent(
event: Event
): boolean;
Dispatches a synthetic event event to target and returns true if either event's cancelable attribute value is false or its preventDefault() method was not invoked, and false otherwise.
MDN Reference
removeEventListener<K extends 'abort'>(
type: K,
listener: (this: AbortSignal, ev: AbortSignalEventMap[K]) => any,
options?: boolean | EventListenerOptions
): void;
Removes the event listener in target's event listener list with the same type, callback, and options.
MDN Reference
throwIfAborted(): void;
static abort(
reason?: any
): AbortSignal;
MDN Reference
static any(
signals: AbortSignal[]
): AbortSignal;
MDN Reference
static timeout(
milliseconds: number
): AbortSignal;
MDN Reference

interface FileHandle

readonly fd: number
The numeric file descriptor managed by the {FileHandle} object.
[Symbol.asyncDispose](): Promise<void>;
Calls filehandle.close() and returns a promise that fulfills when the filehandle is closed.
appendFile(
data: string | ArrayBufferView<ArrayBufferLike> | Iterable<unknown, any, any> | AsyncIterable<unknown, any, any>,
options?: null | BufferEncoding | ObjectEncodingOptions & Abortable
): Promise<void>;
Alias of filehandle.writeFile().
When operating on file handles, the mode cannot be changed from what it was set to with fsPromises.open(). Therefore, this is equivalent to filehandle.writeFile().
@returns
Fulfills with undefined upon success.
chmod(
mode: Mode
): Promise<void>;
Modifies the permissions on the file. See chmod(2).
@param mode
the file mode bit mask.
@returns
Fulfills with undefined upon success.
chown(
uid: number,
gid: number
): Promise<void>;
Changes the ownership of the file. A wrapper for chown(2).
@param uid
The file's new owner's user id.
@param gid
The file's new group's group id.
@returns
Fulfills with undefined upon success.

close(): Promise<void>;

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

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

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

@returns

Fulfills with undefined upon success.

createReadStream(
options?: CreateReadStreamOptions
): ReadStream;
Unlike the 16 KiB default highWaterMark for a stream.Readable, the stream returned by this method has a default highWaterMark of 64 KiB.
options can include start and end values to read a range of bytes from the file instead of the entire file. Both start and end are inclusive and start counting at 0, allowed values are in the [0, Number.MAX_SAFE_INTEGER] range. If start is omitted or undefined, filehandle.createReadStream() reads sequentially from the current file position. The encoding can be any one of those accepted by Buffer.
If the FileHandle points to a character device that only supports blocking reads (such as keyboard or sound card), read operations do not finish until data is available. This can prevent the process from exiting and the stream from closing naturally.
By default, the stream will emit a 'close' event after it has been destroyed. Set the emitClose option to false to change this behavior.
import { open } from 'node:fs/promises'; const fd = await open('/dev/input/event0'); // Create a stream from some character device. const stream = fd.createReadStream(); setTimeout(() => { stream.close(); // This may not close the stream. // Artificially marking end-of-stream, as if the underlying resource had // indicated end-of-file by itself, allows the stream to close. // This does not cancel pending read operations, and if there is such an // operation, the process may still not be able to exit successfully // until it finishes. stream.push(null); stream.read(0); }, 100);
If autoClose is false, then the file descriptor won't be closed, even if there's an error. It is the application's responsibility to close it and make sure there's no file descriptor leak. If autoClose is set to true (default behavior), on 'error' or 'end' the file descriptor will be closed automatically.
An example to read the last 10 bytes of a file which is 100 bytes long:
import { open } from 'node:fs/promises'; const fd = await open('sample.txt'); fd.createReadStream({ start: 90, end: 99 });
createWriteStream(
options?: CreateWriteStreamOptions
): 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.
datasync(): Promise<void>;
Forces all currently queued I/O operations associated with the file to the operating system's synchronized I/O completion state. Refer to the POSIX fdatasync(2) documentation for details.
Unlike filehandle.sync this method does not flush modified metadata.
@returns
Fulfills with undefined upon success.

pull(

...transforms: Transform[]

): ByteReadableStream;

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 });

pull(

...args: [...transforms: Transform[], options: PullOptions]

): ByteReadableStream;

read<T extends ArrayBufferView<ArrayBufferLike>>(
buffer: T,
offset?: null | number,
length?: null | number,
position?: null | ReadPosition
): Promise<FileReadResult<T>>;
Reads data from the file and stores that in the given buffer.
If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero.
@param buffer
A buffer that will be filled with the file data read.
@param offset
The location in the buffer at which to start filling.
@param length
The number of bytes to read.
@param position
The location where to begin reading data from the file. If null, data will be read from the current file position, and the position will be updated. If position is an integer, the current file position will remain unchanged.
@returns
Fulfills upon success with an object with two properties:
read<T extends ArrayBufferView<ArrayBufferLike>>(
buffer: T,
options?: ReadOptions
): Promise<FileReadResult<T>>;
read<T extends ArrayBufferView<ArrayBufferLike> = NonSharedBuffer>(
options?: ReadOptionsWithBuffer<T>
): Promise<FileReadResult<T>>;
readableWebStream(
options?: ReadableWebStreamOptions
): ReadableStream;
Returns a byte-oriented ReadableStream that may be used to read the file's contents.
An error will be thrown if this method is called more than once or is called after the FileHandle is closed or closing.
import { open, } from 'node:fs/promises'; const file = await open('./some/file/to/read'); for await (const chunk of file.readableWebStream()) console.log(chunk); await file.close();
While the ReadableStream will read the file to completion, it will not close the FileHandle automatically. User code must still call thefileHandle.close() method.
readFile<T extends ArrayBufferView<ArrayBufferLike>>(
options: Omit<ReadFileOptionsWithBuffer<T>, 'flag'>
): Promise<BufferView<T>>;
Asynchronously reads the entire contents of a file.
If options is a string, then it specifies the encoding.
If buffer is provided and no encoding is specified, the returned {Buffer} is a view over the supplied buffer containing only the bytes read. If the supplied buffer is too small to contain the entire file, the operation will fail.
The FileHandle has to support reading.
If one or more filehandle.read() calls are made on a file handle and then a filehandle.readFile() call is made, the data will be read from the current position till the end of the file. It doesn't always read from the beginning of the file.
An example using the buffer option with a pre-allocated buffer:
import { Buffer } from 'node:buffer'; import { open } from 'node:fs/promises'; const file = await open('./some/file/to/read'); try { const buf = Buffer.alloc(16384); const contents = await file.readFile({ buffer: buf }); console.log(contents); // A view over `buf` containing only the bytes read } finally { await file.close(); }
An example using the buffer option with a function returning a buffer:
import { Buffer } from 'node:buffer'; import { open } from 'node:fs/promises'; const file = await open('./some/file/to/read'); try { const contents = await file.readFile({ buffer: (size) => Buffer.alloc(size), }); console.log(contents); } finally { await file.close(); }
@returns
Fulfills upon a successful read with the contents of the file. If no encoding is specified (using options.encoding), the data is returned as a Buffer object. Otherwise, the data will be a string.
readFile(
options?: null | Omit<ReadFileOptionsWithBufferEncoding, 'flag'>
): Promise<NonSharedBuffer>;
readFile(
options: BufferEncoding | Omit<ReadFileOptionsWithStringEncoding, 'flag'>
): Promise<string>;
readFile(
options: null | BufferEncoding | Omit<ReadFileOptions, 'flag'>
): Promise<string | NonSharedBuffer>;

readLines(

options?: CreateReadStreamOptions

): Interface;

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);
}

readv<TBuffers extends readonly ArrayBufferView<ArrayBufferLike>[]>(
buffers: TBuffers,
position?: number
): Promise<ReadVResult<TBuffers>>;
Read from a file and write to an array of ArrayBufferView s
@param position
The offset from the beginning of the file where the data should be read from. If position is not a number, the data will be read from the current position.
@returns
Fulfills upon success an object containing two properties:
stat(
opts?: StatOptions & { bigint: false }
): Promise<Stats>;
@returns
Fulfills with an {fs.Stats} for the file.
stat(
opts: StatOptions & { bigint: true }
): Promise<BigIntStats>;
stat(
opts?: StatOptions
): Promise<Stats | BigIntStats>;
sync(): Promise<void>;
Request that all data for the open file descriptor is flushed to the storage device. The specific implementation is operating system and device specific. Refer to the POSIX fsync(2) documentation for more detail.
@returns
Fulfills with undefined upon success.
truncate(
len?: number
): Promise<void>;
Truncates the file.
If the file was larger than len bytes, only the first len bytes will be retained in the file.
The following example retains only the first four bytes of the file:
import { open } from 'node:fs/promises'; let filehandle = null; try { filehandle = await open('temp.txt', 'r+'); await filehandle.truncate(4); } finally { await filehandle?.close(); }
If the file previously was shorter than len bytes, it is extended, and the extended part is filled with null bytes ('\0'):
If len is negative then 0 will be used.
@returns
Fulfills with undefined upon success.
utimes(
atime: TimeLike,
mtime: TimeLike
): Promise<void>;
Change the file system timestamps of the object referenced by the FileHandle then fulfills the promise with no arguments upon success.
write<TBuffer extends ArrayBufferView<ArrayBufferLike>>(
buffer: TBuffer,
offset?: null | number,
length?: null | number,
position?: null | number
): Promise<{ buffer: TBuffer; bytesWritten: number }>;
Write buffer to the file.
The promise is fulfilled with an object containing two properties:
It is unsafe to use filehandle.write() multiple times on the same file without waiting for the promise to be fulfilled (or rejected). For this scenario, use filehandle.createWriteStream().
On Linux, positional writes do not work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
@param offset
The start position from within buffer where the data to write begins.
@param length
The number of bytes from buffer to write.
@param position
The offset from the beginning of the file where the data from buffer should be written. If position is not a number, the data will be written at the current position. See the POSIX pwrite(2) documentation for more detail.
write<TBuffer extends Uint8Array<ArrayBufferLike>>(
buffer: TBuffer,
options?: { length: number; offset: number; position: number }
): Promise<{ buffer: TBuffer; bytesWritten: number }>;
write(
data: string,
position?: null | number,
encoding?: null | BufferEncoding
): Promise<{ buffer: string; bytesWritten: number }>;
writeFile(
data: string | ArrayBufferView<ArrayBufferLike> | Iterable<unknown, any, any> | AsyncIterable<unknown, any, any>,
options?: null | BufferEncoding | ObjectEncodingOptions & Abortable
): Promise<void>;
Asynchronously writes data to a file, replacing the file if it already exists. data can be a string, a buffer, an AsyncIterable, or an Iterable object. The promise is fulfilled with no arguments upon success.
If options is a string, then it specifies the encoding.
The FileHandle has to support writing.
It is unsafe to use filehandle.writeFile() multiple times on the same file without waiting for the promise to be fulfilled (or rejected).
If one or more filehandle.write() calls are made on a file handle and then afilehandle.writeFile() call is made, the data will be written from the current position till the end of the file. It doesn't always write from the beginning of the file.
writer(
options?: WriterOptions
): Writer;
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 w = dst.writer({ limit: 1024 * 1024 }); // Max 1 MB await pipeTo(src.pull({ autoClose: true }), w); await w.end(); await dst.close();
writev<TBuffers extends readonly ArrayBufferView<ArrayBufferLike>[]>(
buffers: TBuffers,
position?: number
): Promise<WriteVResult<TBuffers>>;
Write an array of ArrayBufferView s to the file.
The promise is fulfilled with an object containing a two properties:
It is unsafe to call writev() multiple times on the same file without waiting for the promise to be fulfilled (or rejected).
On Linux, positional writes don't work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.
@param position
The offset from the beginning of the file where the data from buffers should be written. If position is not a number, the data will be written at the current position.

interface ReadableStream<R = any>

readonly locked: boolean
cancel(
reason?: any
): Promise<void>;
getReader(
options: { mode: 'byob' }
): ReadableStreamBYOBReader;
getReader(): ReadableStreamDefaultReader<R>;
getReader(
options?: ReadableStreamGetReaderOptions
): ReadableStreamReader<R>;
pipeThrough<T>(
transform: ReadableWritablePair<T, R>,
options?: StreamPipeOptions
): ReadableStream<T>;
pipeTo(
destination: WritableStream<R>,
options?: StreamPipeOptions
): Promise<void>;
tee(): [ReadableStream<R>, ReadableStream<R>];
values(
options?: ReadableStreamIteratorOptions
): ReadableStreamAsyncIterator<R>;

interface WritableStream<W = any>

readonly locked: boolean
abort(
reason?: any
): Promise<void>;
close(): Promise<void>;
getWriter(): WritableStreamDefaultWriter<W>;

interface TransformStream<I = any, O = any>

readonly readable: ReadableStream<O>
readonly writable: WritableStream<I>

class Server

This class is used to create a TCP or IPC server.

connections: number
readonly listening: boolean
Indicates whether or not the server is listening for connections.
maxConnections: number
Set this property to reject connections when the server's connection count gets high.
It is not recommended to use this option once a socket has been sent to a child with child_process.fork().
[Symbol.asyncDispose](): Promise<void>;
Calls () and returns a promise that fulfills when the server has closed.

[events.captureRejectionSymbol](

error: Error,

event: string | symbol,

...args: any[]

): void;

The Symbol.for('nodejs.rejection') method is called in case a promise rejection happens when emitting an event and captureRejections is enabled on the emitter. It is possible to use events.captureRejectionSymbol in place of Symbol.for('nodejs.rejection').

import { EventEmitter, captureRejectionSymbol } from 'node:events';

class MyClass extends EventEmitter {
  constructor() {
    super({ captureRejections: true });
  }

  [captureRejectionSymbol](err, event, ...args) {
    console.log('rejection happened for', event, 'with', err, ...args);
    this.destroy(err);
  }

  destroy(err) {
    // Tear the resource down here.
  }
}

addListener<E extends keyof ServerEventMap>(
eventName: E,
listener: (...args: ServerEventMap[E]) => void
): this;
Alias for emitter.on(eventName, listener).
addListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Alias for emitter.on(eventName, listener).
address(): null | string | AddressInfo;
Returns the bound address, the address family name, and port of the server as reported by the operating system if listening on an IP socket (useful to find which port was assigned when getting an OS-assigned address):{ port: 12346, family: 'IPv4', address: '127.0.0.1' }.
For a server listening on a pipe or Unix domain socket, the name is returned as a string.
const server = net.createServer((socket) => { socket.end('goodbye\n'); }).on('error', (err) => { // Handle errors here. throw err; }); // Grab an arbitrary unused port. server.listen(() => { console.log('opened server on', server.address()); });
server.address() returns null before the 'listening' event has been emitted or after calling server.close().
close(
callback?: (err?: Error) => void
): this;
Stops the server from accepting new connections and keeps existing connections. This function is asynchronous, the server is finally closed when all connections are ended and the server emits a 'close' event. The optional callback will be called once the 'close' event occurs. Unlike that event, it will be called with an Error as its only argument if the server was not open when it was closed.
@param callback
Called when the server is closed.

emit<E extends keyof ServerEventMap>(

eventName: E,

...args: ServerEventMap[E]

): boolean;

Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments to each.

Returns true if the event had listeners, false otherwise.

import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();

// First listener
myEmitter.on('event', function firstListener() {
  console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
  console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
  const parameters = args.join(', ');
  console.log(`event with parameters ${parameters} in third listener`);
});

console.log(myEmitter.listeners('event'));

myEmitter.emit('event', 1, 2, 3, 4, 5);

// Prints:
// [
//   [Function: firstListener],
//   [Function: secondListener],
//   [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener

emit(

eventName: string | symbol,

...args: any[]

): boolean;

Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments to each.

Returns true if the event had listeners, false otherwise.

import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();

// First listener
myEmitter.on('event', function firstListener() {
  console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
  console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
  const parameters = args.join(', ');
  console.log(`event with parameters ${parameters} in third listener`);
});

console.log(myEmitter.listeners('event'));

myEmitter.emit('event', 1, 2, 3, 4, 5);

// Prints:
// [
//   [Function: firstListener],
//   [Function: secondListener],
//   [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener

eventNames(): string | symbol[];

Returns an array listing the events for which the emitter has registered listeners.

import { EventEmitter } from 'node:events';

const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});

const sym = Symbol('symbol');
myEE.on(sym, () => {});

console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]

getConnections(
cb: (error: null | Error, count: number) => void
): this;
Asynchronously get the number of concurrent connections on the server. Works when sockets were sent to forks.
Callback should take two arguments err and count.
getMaxListeners(): number;
Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to events.defaultMaxListeners.
listen(
port?: number,
hostname?: string,
backlog?: number,
listeningListener?: () => void
): this;
Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.
Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers
This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.
All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).
All Socket are set to SO_REUSEADDR (see socket(7) for details).
The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.
One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:
server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listen(
port?: number,
hostname?: string,
listeningListener?: () => void
): this;
Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.
Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers
This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.
All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).
All Socket are set to SO_REUSEADDR (see socket(7) for details).
The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.
One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:
server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listen(
port?: number,
backlog?: number,
listeningListener?: () => void
): this;
Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.
Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers
This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.
All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).
All Socket are set to SO_REUSEADDR (see socket(7) for details).
The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.
One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:
server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listen(
port?: number,
listeningListener?: () => void
): this;
Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.
Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers
This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.
All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).
All Socket are set to SO_REUSEADDR (see socket(7) for details).
The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.
One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:
server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listen(
path: string,
backlog?: number,
listeningListener?: () => void
): this;
Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.
Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers
This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.
All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).
All Socket are set to SO_REUSEADDR (see socket(7) for details).
The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.
One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:
server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listen(
path: string,
listeningListener?: () => void
): this;
Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.
Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers
This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.
All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).
All Socket are set to SO_REUSEADDR (see socket(7) for details).
The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.
One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:
server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listen(
options: ListenOptions,
listeningListener?: () => void
): this;
Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.
Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers
This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.
All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).
All Socket are set to SO_REUSEADDR (see socket(7) for details).
The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.
One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:
server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listen(
handle: any,
backlog?: number,
listeningListener?: () => void
): this;
Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.
Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers
This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.
All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).
All Socket are set to SO_REUSEADDR (see socket(7) for details).
The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.
One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:
server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listen(
handle: any,
listeningListener?: () => void
): this;
Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.
Possible signatures:
server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers
This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callbackwill be added as a listener for the 'listening' event.
All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).
All Socket are set to SO_REUSEADDR (see socket(7) for details).
The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.
One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requestedport/path/handle. One way to handle this would be to retry after a certain amount of time:
server.on('error', (e) => { if (e.code === 'EADDRINUSE') { console.error('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
listenerCount<E extends keyof ServerEventMap>(
eventName: E,
listener?: (...args: ServerEventMap[E]) => void
): number;
Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.
@param eventName
The name of the event being listened for
@param listener
The event handler function
listenerCount(
eventName: string | symbol,
listener?: (...args: any[]) => void
): number;
Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.
@param eventName
The name of the event being listened for
@param listener
The event handler function

listeners<E extends keyof ServerEventMap>(

eventName: E

): (...args: ServerEventMap[E]) => void[];

Returns a copy of the array of listeners for the event named eventName.

server.on('connection', (stream) => {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]

listeners(

eventName: string | symbol

): (...args: any[]) => void[];

Returns a copy of the array of listeners for the event named eventName.

server.on('connection', (stream) => {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]

off<E extends keyof ServerEventMap>(
eventName: E,
listener: (...args: ServerEventMap[E]) => void
): this;
Alias for emitter.removeListener().
off(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Alias for emitter.removeListener().
on<E extends keyof ServerEventMap>(
eventName: E,
listener: (...args: ServerEventMap[E]) => void
): this;
Adds the listener function to the end of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
server.on('connection', (stream) => { console.log('someone connected!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => console.log('a')); myEE.prependListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
on(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Adds the listener function to the end of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
server.on('connection', (stream) => { console.log('someone connected!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => console.log('a')); myEE.prependListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
once<E extends keyof ServerEventMap>(
eventName: E,
listener: (...args: ServerEventMap[E]) => void
): this;
Adds a one-time listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.
server.once('connection', (stream) => { console.log('Ah, we have our first user!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependOnceListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.once('foo', () => console.log('a')); myEE.prependOnceListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
once(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Adds a one-time listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.
server.once('connection', (stream) => { console.log('Ah, we have our first user!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependOnceListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.once('foo', () => console.log('a')); myEE.prependOnceListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
prependListener<E extends keyof ServerEventMap>(
eventName: E,
listener: (...args: ServerEventMap[E]) => void
): this;
Adds the listener function to the beginning of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
server.prependListener('connection', (stream) => { console.log('someone connected!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function
prependListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Adds the listener function to the beginning of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
server.prependListener('connection', (stream) => { console.log('someone connected!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function
prependOnceListener<E extends keyof ServerEventMap>(
eventName: E,
listener: (...args: ServerEventMap[E]) => void
): this;
Adds a one-time listener function for the event named eventName to the beginning of the listeners array. The next time eventName is triggered, this listener is removed, and then invoked.
server.prependOnceListener('connection', (stream) => { console.log('Ah, we have our first user!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function
prependOnceListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Adds a one-time listener function for the event named eventName to the beginning of the listeners array. The next time eventName is triggered, this listener is removed, and then invoked.
server.prependOnceListener('connection', (stream) => { console.log('Ah, we have our first user!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function

rawListeners<E extends keyof ServerEventMap>(

eventName: E

): (...args: ServerEventMap[E]) => void[];

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');

// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');

rawListeners(

eventName: string | symbol

): (...args: any[]) => void[];

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');

// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');

ref(): this;
Opposite of unref(), calling ref() on a previously unrefed server will not let the program exit if it's the only server left (the default behavior). If the server is refed calling ref() again will have no effect.
removeAllListeners<E extends keyof ServerEventMap>(
eventName?: E
): this;
Removes all listeners, or those of the specified eventName.
It is bad practice to remove listeners added elsewhere in the code, particularly when the EventEmitter instance was created by some other component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter, so that calls can be chained.
removeAllListeners(
eventName?: string | symbol
): this;
Removes all listeners, or those of the specified eventName.
It is bad practice to remove listeners added elsewhere in the code, particularly when the EventEmitter instance was created by some other component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter, so that calls can be chained.
removeListener<E extends keyof ServerEventMap>(
eventName: E,
listener: (...args: ServerEventMap[E]) => void
): this;
Removes the specified listener from the listener array for the event named eventName.
const callback = (stream) => { console.log('someone connected!'); }; server.on('connection', callback); // ... server.removeListener('connection', callback);
removeListener() will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified eventName, then removeListener() must be called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution will not remove them from emit() in progress. Subsequent events behave as expected.
import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); const callbackA = () => { console.log('A'); myEmitter.removeListener('event', callbackB); }; const callbackB = () => { console.log('B'); }; myEmitter.on('event', callbackA); myEmitter.on('event', callbackB); // callbackA removes listener callbackB but it will still be called. // Internal listener array at time of emit [callbackA, callbackB] myEmitter.emit('event'); // Prints: // A // B // callbackB is now removed. // Internal listener array [callbackA] myEmitter.emit('event'); // Prints: // A
Because listeners are managed using an internal array, calling this will change the position indexes of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the emitter.listeners() method will need to be recreated.
When a single function has been added as a handler multiple times for a single event (as in the example below), removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:
import { EventEmitter } from 'node:events'; const ee = new EventEmitter(); function pong() { console.log('pong'); } ee.on('ping', pong); ee.once('ping', pong); ee.removeListener('ping', pong); ee.emit('ping'); ee.emit('ping');
Returns a reference to the EventEmitter, so that calls can be chained.
removeListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
Removes the specified listener from the listener array for the event named eventName.
const callback = (stream) => { console.log('someone connected!'); }; server.on('connection', callback); // ... server.removeListener('connection', callback);
removeListener() will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified eventName, then removeListener() must be called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution will not remove them from emit() in progress. Subsequent events behave as expected.
import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); const callbackA = () => { console.log('A'); myEmitter.removeListener('event', callbackB); }; const callbackB = () => { console.log('B'); }; myEmitter.on('event', callbackA); myEmitter.on('event', callbackB); // callbackA removes listener callbackB but it will still be called. // Internal listener array at time of emit [callbackA, callbackB] myEmitter.emit('event'); // Prints: // A // B // callbackB is now removed. // Internal listener array [callbackA] myEmitter.emit('event'); // Prints: // A
Because listeners are managed using an internal array, calling this will change the position indexes of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the emitter.listeners() method will need to be recreated.
When a single function has been added as a handler multiple times for a single event (as in the example below), removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:
import { EventEmitter } from 'node:events'; const ee = new EventEmitter(); function pong() { console.log('pong'); } ee.on('ping', pong); ee.once('ping', pong); ee.removeListener('ping', pong); ee.emit('ping'); ee.emit('ping');
Returns a reference to the EventEmitter, so that calls can be chained.
setMaxListeners(
n: number
): this;
By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default that helps finding memory leaks. The emitter.setMaxListeners() method allows the limit to be modified for this specific EventEmitter instance. The value can be set to Infinity (or 0) to indicate an unlimited number of listeners.
Returns a reference to the EventEmitter, so that calls can be chained.
unref(): this;
Calling unref() on a server will allow the program to exit if this is the only active server in the event system. If the server is already unrefed callingunref() again will have no effect.

class Socket

This class is an abstraction of a TCP socket or a streaming IPC endpoint (uses named pipes on Windows, and Unix domain sockets otherwise). It is also an EventEmitter.

A net.Socket can be created by the user and used directly to interact with a server. For example, it is returned by createConnection, so the user can use it to talk to the server.

It can also be created by Node.js and passed to the user when a connection is received. For example, it is passed to the listeners of a 'connection' event emitted on a Server, so the user can use it to interact with the client.

allowHalfOpen: boolean
If false then the stream will automatically end the writable side when the readable side ends. Set initially by the allowHalfOpen constructor option, which defaults to true.
This can be changed manually to change the half-open behavior of an existing Duplex stream instance, but must be changed before the 'end' event is emitted.
readonly autoSelectFamilyAttemptedAddresses: string[]
This property is only present if the family autoselection algorithm is enabled in socket.connect(options) and it is an array of the addresses that have been attempted.
Each address is a string in the form of $IP:$PORT. If the connection was successful, then the last address is the one that the socket is currently connected to.
readonly bytesRead: number
The amount of received bytes.
readonly bytesWritten: number
The amount of bytes sent.
readonly closed: boolean
Is true after 'close' has been emitted.
readonly connecting: boolean
If true, socket.connect(options[, connectListener]) was called and has not yet finished. It will stay true until the socket becomes connected, then it is set to false and the 'connect' event is emitted. Note that the socket.connect(options[, connectListener]) callback is a listener for the 'connect' event.
readonly destroyed: boolean
See writable.destroyed for further details.
readonly errored: null | Error
Returns error if the stream has been destroyed with an error.
readonly localAddress?: string
The string representation of the local IP address the remote client is connecting on. For example, in a server listening on '0.0.0.0', if a client connects on '192.168.1.1', the value of socket.localAddress would be'192.168.1.1'.
readonly localFamily?: string
The string representation of the local IP family. 'IPv4' or 'IPv6'.
readonly localPort?: number
The numeric representation of the local port. For example, 80 or 21.
readonly pending: boolean
This is true if the socket is not connected yet, either because .connect()has not yet been called or because it is still in the process of connecting (see socket.connecting).
readable: boolean
Is true if it is safe to call read, which means the stream has not been destroyed or emitted 'error' or 'end'.
readonly readableAborted: boolean
Returns whether the stream was destroyed or errored before emitting 'end'.
readonly readableDidRead: boolean
Returns whether 'data' has been emitted.
readonly readableEncoding: null | BufferEncoding
Getter for the property encoding of a given Readable stream. The encoding property can be set using the setEncoding method.
readonly readableEnded: boolean
Becomes true when 'end' event is emitted.
readableFlowing: null | boolean
This property reflects the current state of a Readable stream as described in the Three states section.
readonly readableHighWaterMark: number
Returns the value of highWaterMark passed when creating this Readable.
readonly readableLength: number
This property contains the number of bytes (or objects) in the queue ready to be read. The value provides introspection data regarding the status of the highWaterMark.
readonly readableObjectMode: boolean
Getter for the property objectMode of a given Readable stream.
readonly readyState: SocketReadyState
This property represents the state of the connection as a string.
If the socket is connecting, socket.readyState is opening.
If the socket is readable and writable, it is open.
If the socket is readable and not writable, it is readOnly.
If the socket is not readable and writable, it is writeOnly.
Otherwise, it is closed.
readonly remoteAddress: undefined | string
The string representation of the remote IP address. For example,'74.125.127.100' or '2001:4860:a005::68'. Value may be undefined if the socket is destroyed (for example, if the client disconnected).
readonly remoteFamily: undefined | string
The string representation of the remote IP family. 'IPv4' or 'IPv6'. Value may be undefined if the socket is destroyed (for example, if the client disconnected).
readonly remotePort: undefined | number
The numeric representation of the remote port. For example, 80 or 21. Value may be undefined if the socket is destroyed (for example, if the client disconnected).
readonly server: null | Server
Reference to the server that accepted the socket. This is null for sockets that were not accepted by a server.
readonly timeout?: number
The socket timeout in milliseconds as set by socket.setTimeout(). It is undefined if a timeout has not been set.
writable: boolean
Is true if it is safe to call writable.write(), which means the stream has not been destroyed, errored, or ended.
readonly writableAborted: boolean
Returns whether the stream was destroyed or errored before emitting 'finish'.
readonly writableCorked: number
Number of times writable.uncork() needs to be called in order to fully uncork the stream.
readonly writableEnded: boolean
Is true after writable.end() has been called. This property does not indicate whether the data has been flushed, for this use writable.writableFinished instead.
readonly writableFinished: boolean
Is set to true immediately before the 'finish' event is emitted.
readonly writableHighWaterMark: number
Return the value of highWaterMark passed when creating this Writable.
readonly writableLength: number
This property contains the number of bytes (or objects) in the queue ready to be written. The value provides introspection data regarding the status of the highWaterMark.
readonly writableNeedDrain: boolean
Is true if the stream's buffer has been full and stream will emit 'drain'.
readonly writableObjectMode: boolean
Getter for the property objectMode of a given Writable stream.
_construct(
callback: (error?: null | Error) => void
): void;
_destroy(
error: null | Error,
callback: (error?: null | Error) => void
): void;
_final(
callback: (error?: null | Error) => void
): void;
_read(
size: number
): void;
_write(
chunk: any,
encoding: BufferEncoding,
callback: (error?: null | Error) => void
): void;
_writev(
chunks: { chunk: any; encoding: BufferEncoding }[],
callback: (error?: null | Error) => void
): void;
[Symbol.asyncDispose](): Promise<void>;
Calls readable.destroy() with an AbortError and returns a promise that fulfills when the stream is finished.
[Symbol.asyncIterator](): AsyncIterator<any>;
@returns
AsyncIterator to fully consume the stream.

[events.captureRejectionSymbol](

error: Error,

event: string | symbol,

...args: any[]

): void;

import { EventEmitter, captureRejectionSymbol } from 'node:events';

class MyClass extends EventEmitter {
  constructor() {
    super({ captureRejections: true });
  }

  [captureRejectionSymbol](err, event, ...args) {
    console.log('rejection happened for', event, 'with', err, ...args);
    this.destroy(err);
  }

  destroy(err) {
    // Tear the resource down here.
  }
}

[toAsyncStreamable](): ByteReadableStream;
When the --experimental-stream-iter flag is enabled, Readable streams implement the Stream.toAsyncStreamable protocol, enabling efficient consumption by the stream/iter API.
This provides a batched async iterator that drains the stream's internal buffer into Uint8Array[] batches, amortizing the per-chunk Promise overhead of the standard Symbol.asyncIterator path. For byte-mode streams, chunks are yielded directly as Buffer instances (which are Uint8Array subclasses). For object-mode or encoded streams, each chunk is normalized to Uint8Array before batching.
The returned iterator is tagged as a validated source, so from() passes it through without additional normalization.
import { Readable } from 'node:stream'; import { text, from } from 'node:stream/iter'; const readable = new Readable({ read() { this.push('hello'); this.push(null); }, }); // Readable is automatically consumed via toAsyncStreamable console.log(await text(from(readable))); // 'hello'
Without the --experimental-stream-iter flag, calling this method throws ERR_STREAM_ITER_MISSING_FLAG.
addListener<E extends keyof SocketEventMap>(
eventName: E,
listener: (...args: SocketEventMap[E]) => void
): this;
Alias for emitter.on(eventName, listener).
addListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
address(): {} | AddressInfo;
Returns the bound address, the address family name and port of the socket as reported by the operating system:{ port: 12346, family: 'IPv4', address: '127.0.0.1' }

compose(

stream: WritableStream | WritableStream<any> | TransformStream<any, any> | (source: any) => void,

options?: Abortable

): Duplex;

import { Readable } from 'node:stream';

async function* splitToWords(source) {
  for await (const chunk of source) {
    const words = String(chunk).split(' ');

    for (const word of words) {
      yield word;
    }
  }
}

const wordsStream = Readable.from(['text passed through', 'composed stream']).compose(splitToWords);
const words = await wordsStream.toArray();

console.log(words); // prints ['text', 'passed', 'through', 'composed', 'stream']

readable.compose(s) is equivalent to stream.compose(readable, s).

This method also allows for an AbortSignal to be provided, which will destroy the composed stream when aborted.

See stream.compose(...streams) for more information.

@returns

a stream composed with the stream stream.

connect(
options: SocketConnectOpts,
connectionListener?: () => void
): this;
Initiate a connection on a given socket.
Possible signatures:
socket.connect(options[, connectListener])
socket.connect(path[, connectListener]) for IPC connections.
socket.connect(port[, host][, connectListener]) for TCP connections.
Returns: net.Socket The socket itself.
This function is asynchronous. When the connection is established, the 'connect' event will be emitted. If there is a problem connecting, instead of a 'connect' event, an 'error' event will be emitted with the error passed to the 'error' listener. The last parameter connectListener, if supplied, will be added as a listener for the 'connect' event once.
This function should only be used for reconnecting a socket after'close' has been emitted or otherwise it may lead to undefined behavior.
connect(
port: number,
host: string,
connectionListener?: () => void
): this;
Initiate a connection on a given socket.
Possible signatures:
socket.connect(options[, connectListener])
socket.connect(path[, connectListener]) for IPC connections.
socket.connect(port[, host][, connectListener]) for TCP connections.
Returns: net.Socket The socket itself.
This function is asynchronous. When the connection is established, the 'connect' event will be emitted. If there is a problem connecting, instead of a 'connect' event, an 'error' event will be emitted with the error passed to the 'error' listener. The last parameter connectListener, if supplied, will be added as a listener for the 'connect' event once.
This function should only be used for reconnecting a socket after'close' has been emitted or otherwise it may lead to undefined behavior.
connect(
port: number,
connectionListener?: () => void
): this;
Initiate a connection on a given socket.
Possible signatures:
socket.connect(options[, connectListener])
socket.connect(path[, connectListener]) for IPC connections.
socket.connect(port[, host][, connectListener]) for TCP connections.
Returns: net.Socket The socket itself.
This function is asynchronous. When the connection is established, the 'connect' event will be emitted. If there is a problem connecting, instead of a 'connect' event, an 'error' event will be emitted with the error passed to the 'error' listener. The last parameter connectListener, if supplied, will be added as a listener for the 'connect' event once.
This function should only be used for reconnecting a socket after'close' has been emitted or otherwise it may lead to undefined behavior.
connect(
path: string,
connectionListener?: () => void
): this;
Initiate a connection on a given socket.
Possible signatures:
socket.connect(options[, connectListener])
socket.connect(path[, connectListener]) for IPC connections.
socket.connect(port[, host][, connectListener]) for TCP connections.
Returns: net.Socket The socket itself.
This function is asynchronous. When the connection is established, the 'connect' event will be emitted. If there is a problem connecting, instead of a 'connect' event, an 'error' event will be emitted with the error passed to the 'error' listener. The last parameter connectListener, if supplied, will be added as a listener for the 'connect' event once.
This function should only be used for reconnecting a socket after'close' has been emitted or otherwise it may lead to undefined behavior.
cork(): void;
The writable.cork() method forces all written data to be buffered in memory. The buffered data will be flushed when either the uncork or end methods are called.
The primary intent of writable.cork() is to accommodate a situation in which several small chunks are written to the stream in rapid succession. Instead of immediately forwarding them to the underlying destination, writable.cork() buffers all the chunks until writable.uncork() is called, which will pass them all to writable._writev(), if present. This prevents a head-of-line blocking situation where data is being buffered while waiting for the first small chunk to be processed. However, use of writable.cork() without implementing writable._writev() may have an adverse effect on throughput.
See also: writable.uncork(), writable._writev().
destroy(
error?: Error
): this;
Destroy the stream. Optionally emit an 'error' event, and emit a 'close' event (unless emitClose is set to false). After this call, the readable stream will release any internal resources and subsequent calls to push() will be ignored.
Once destroy() has been called any further calls will be a no-op and no further errors except from _destroy() may be emitted as 'error'.
Implementors should not override this method, but instead implement readable._destroy().
@param error
Error which will be passed as payload in 'error' event
destroySoon(): void;
Destroys the socket after all data is written. If the finish event was already emitted the socket is destroyed immediately. If the socket is still writable it implicitly calls socket.end().
drop(
limit: number,
options?: Abortable
): Readable;
This method returns a new stream with the first limit chunks dropped from the start.
@param limit
the number of chunks to drop from the readable.
@returns
a stream with limit chunks dropped from the start.

emit<E extends keyof SocketEventMap>(

eventName: E,

...args: SocketEventMap[E]

): boolean;

Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments to each.

Returns true if the event had listeners, false otherwise.

import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();

// First listener
myEmitter.on('event', function firstListener() {
  console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
  console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
  const parameters = args.join(', ');
  console.log(`event with parameters ${parameters} in third listener`);
});

console.log(myEmitter.listeners('event'));

myEmitter.emit('event', 1, 2, 3, 4, 5);

// Prints:
// [
//   [Function: firstListener],
//   [Function: secondListener],
//   [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener

emit(

eventName: string | symbol,

...args: any[]

): boolean;

end(
callback?: () => void
): this;
Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data.
See writable.end() for further details.
@param callback
Optional callback for when the socket is finished.
@returns
The socket itself.
end(
buffer: string | Uint8Array<ArrayBufferLike>,
callback?: () => void
): this;
Half-closes the socket, with one final chunk of data.
@param callback
Optional callback for when the socket is finished.
@returns
The socket itself.
end(
str: string | Uint8Array<ArrayBufferLike>,
encoding?: BufferEncoding,
callback?: () => void
): this;
Half-closes the socket, with one final chunk of data.
@param encoding
Only used when data is string.
@param callback
Optional callback for when the socket is finished.
@returns
The socket itself.

eventNames(): string | symbol[];

Returns an array listing the events for which the emitter has registered listeners.

import { EventEmitter } from 'node:events';

const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});

const sym = Symbol('symbol');
myEE.on(sym, () => {});

console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]

every(
fn: (data: any, options?: Abortable) => boolean | Promise<boolean>,
options?: Pick<ReadableOperatorOptions, 'signal' | 'concurrency'>
): Promise<boolean>;
This method is similar to Array.prototype.every and calls fn on each chunk in the stream to check if all awaited return values are truthy value for fn. Once an fn call on a chunk awaited return value is falsy, the stream is destroyed and the promise is fulfilled with false. If all of the fn calls on the chunks return a truthy value, the promise is fulfilled with true.
@param fn
a function to call on each chunk of the stream. Async or not.
@returns
a promise evaluating to true if fn returned a truthy value for every one of the chunks.
filter(
fn: (data: any, options?: Abortable) => boolean | Promise<boolean>,
options?: ReadableOperatorOptions
): Readable;
This method allows filtering the stream. For each chunk in the stream the fn function will be called and if it returns a truthy value, the chunk will be passed to the result stream. If the fn function returns a promise - that promise will be awaited.
@param fn
a function to filter chunks from the stream. Async or not.
@returns
a stream filtered with the predicate fn.
find<T>(
fn: (data: any, options?: Abortable) => data is T,
options?: Pick<ReadableOperatorOptions, 'signal' | 'concurrency'>
): Promise<undefined | T>;
This method is similar to Array.prototype.find and calls fn on each chunk in the stream to find a chunk with a truthy value for fn. Once an fn call's awaited return value is truthy, the stream is destroyed and the promise is fulfilled with value for which fn returned a truthy value. If all of the fn calls on the chunks return a falsy value, the promise is fulfilled with undefined.
@param fn
a function to call on each chunk of the stream. Async or not.
@returns
a promise evaluating to the first chunk for which fn evaluated with a truthy value, or undefined if no element was found.
find(
fn: (data: any, options?: Abortable) => boolean | Promise<boolean>,
options?: Pick<ReadableOperatorOptions, 'signal' | 'concurrency'>
): Promise<any>;
This method is similar to Array.prototype.find and calls fn on each chunk in the stream to find a chunk with a truthy value for fn. Once an fn call's awaited return value is truthy, the stream is destroyed and the promise is fulfilled with value for which fn returned a truthy value. If all of the fn calls on the chunks return a falsy value, the promise is fulfilled with undefined.
@param fn
a function to call on each chunk of the stream. Async or not.
@returns
a promise evaluating to the first chunk for which fn evaluated with a truthy value, or undefined if no element was found.
flatMap(
fn: (data: any, options?: Abortable) => any,
options?: Pick<ReadableOperatorOptions, 'signal' | 'concurrency'>
): Readable;
This method returns a new stream by applying the given callback to each chunk of the stream and then flattening the result.
It is possible to return a stream or another iterable or async iterable from fn and the result streams will be merged (flattened) into the returned stream.
@param fn
a function to map over every chunk in the stream. May be async. May be a stream or generator.
@returns
a stream flat-mapped with the function fn.
forEach(
fn: (data: any, options?: Abortable) => void | Promise<void>,
options?: Pick<ReadableOperatorOptions, 'signal' | 'concurrency'>
): Promise<void>;
This method allows iterating a stream. For each chunk in the stream the fn function will be called. If the fn function returns a promise - that promise will be awaited.
This method is different from for await...of loops in that it can optionally process chunks concurrently. In addition, a forEach iteration can only be stopped by having passed a signal option and aborting the related AbortController while for await...of can be stopped with break or return. In either case the stream will be destroyed.
This method is different from listening to the 'data' event in that it uses the readable event in the underlying machinary and can limit the number of concurrent fn calls.
@param fn
a function to call on each chunk of the stream. Async or not.
@returns
a promise for when the stream has finished.
getMaxListeners(): number;
Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to events.defaultMaxListeners.
getTypeOfService(): number;
Returns the current Type of Service (TOS) field for IPv4 packets or Traffic Class for IPv6 packets for this socket.
setTypeOfService() may be called before the socket is connected; the value will be cached and applied when the socket establishes a connection. getTypeOfService() will return the currently set value even before connection.
On some platforms (e.g., Linux), certain TOS/ECN bits may be masked or ignored, and behavior can differ between IPv4 and IPv6 or dual-stack sockets. Callers should verify platform-specific semantics.
@returns
The current TOS value.
isPaused(): boolean;
The readable.isPaused() method returns the current operating state of the Readable. This is used primarily by the mechanism that underlies the readable.pipe() method. In most typical cases, there will be no reason to use this method directly.
const readable = new stream.Readable(); readable.isPaused(); // === false readable.pause(); readable.isPaused(); // === true readable.resume(); readable.isPaused(); // === false
iterator(
options?: ReadableIteratorOptions
): AsyncIterator<any>;
The iterator created by this method gives users the option to cancel the destruction of the stream if the for await...of loop is exited by return, break, or throw, or if the iterator should destroy the stream if the stream emitted an error during iteration.
listenerCount<E extends keyof SocketEventMap>(
eventName: E,
listener?: (...args: SocketEventMap[E]) => void
): number;
Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.
@param eventName
The name of the event being listened for
@param listener
The event handler function
listenerCount(
eventName: string | symbol,
listener?: (...args: any[]) => void
): number;
listeners<E extends keyof SocketEventMap>(
eventName: E
): (...args: SocketEventMap[E]) => void[];
Returns a copy of the array of listeners for the event named eventName.
server.on('connection', (stream) => { console.log('someone connected!'); }); console.log(util.inspect(server.listeners('connection'))); // Prints: [ [Function] ]
listeners(
eventName: string | symbol
): (...args: any[]) => void[];
map(
fn: (data: any, options?: Abortable) => any,
options?: ReadableOperatorOptions
): Readable;
This method allows mapping over the stream. The fn function will be called for every chunk in the stream. If the fn function returns a promise - that promise will be awaited before being passed to the result stream.
@param fn
a function to map over every chunk in the stream. Async or not.
@returns
a stream mapped with the function fn.
off<E extends keyof SocketEventMap>(
eventName: E,
listener: (...args: SocketEventMap[E]) => void
): this;
Alias for emitter.removeListener().
off(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
on<E extends keyof SocketEventMap>(
eventName: E,
listener: (...args: SocketEventMap[E]) => void
): this;
Adds the listener function to the end of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
server.on('connection', (stream) => { console.log('someone connected!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.on('foo', () => console.log('a')); myEE.prependListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
on(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
once<E extends keyof SocketEventMap>(
eventName: E,
listener: (...args: SocketEventMap[E]) => void
): this;
Adds a one-time listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.
server.once('connection', (stream) => { console.log('Ah, we have our first user!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
By default, event listeners are invoked in the order they are added. The emitter.prependOnceListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.
import { EventEmitter } from 'node:events'; const myEE = new EventEmitter(); myEE.once('foo', () => console.log('a')); myEE.prependOnceListener('foo', () => console.log('b')); myEE.emit('foo'); // Prints: // b // a
@param eventName
The name of the event.
@param listener
The callback function
once(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
pause(): this;
Pauses the reading of data. That is, 'data' events will not be emitted. Useful to throttle back an upload.
@returns
The socket itself.
pipe<T extends WritableStream>(
destination: T,
options?: PipeOptions
): T;
prependListener<E extends keyof SocketEventMap>(
eventName: E,
listener: (...args: SocketEventMap[E]) => void
): this;
Adds the listener function to the beginning of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.
server.prependListener('connection', (stream) => { console.log('someone connected!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function
prependListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
prependOnceListener<E extends keyof SocketEventMap>(
eventName: E,
listener: (...args: SocketEventMap[E]) => void
): this;
Adds a one-time listener function for the event named eventName to the beginning of the listeners array. The next time eventName is triggered, this listener is removed, and then invoked.
server.prependOnceListener('connection', (stream) => { console.log('Ah, we have our first user!'); });
Returns a reference to the EventEmitter, so that calls can be chained.
@param eventName
The name of the event.
@param listener
The callback function
prependOnceListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
push(
chunk: any,
encoding?: BufferEncoding
): boolean;

rawListeners<E extends keyof SocketEventMap>(

eventName: E

): (...args: SocketEventMap[E]) => void[];

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');

// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');

rawListeners(

eventName: string | symbol

): (...args: any[]) => void[];

read(
size?: number
): any;
The readable.read() method reads data out of the internal buffer and returns it. If no data is available to be read, null is returned. By default, the data is returned as a Buffer object unless an encoding has been specified using the readable.setEncoding() method or the stream is operating in object mode.
The optional size argument specifies a specific number of bytes to read. If size bytes are not available to be read, null will be returned unless the stream has ended, in which case all of the data remaining in the internal buffer will be returned.
If the size argument is not specified, all of the data contained in the internal buffer will be returned.
The size argument must be less than or equal to 1 GiB.
The readable.read() method should only be called on Readable streams operating in paused mode. In flowing mode, readable.read() is called automatically until the internal buffer is fully drained.
const readable = getReadableStreamSomehow(); // 'readable' may be triggered multiple times as data is buffered in readable.on('readable', () => { let chunk; console.log('Stream is readable (new data received in buffer)'); // Use a loop to make sure we read all currently available data while (null !== (chunk = readable.read())) { console.log(`Read ${chunk.length} bytes of data...`); } }); // 'end' will be triggered once when there is no more data available readable.on('end', () => { console.log('Reached end of stream.'); });
Each call to readable.read() returns a chunk of data, or null. The chunks are not concatenated. A while loop is necessary to consume all data currently in the buffer. When reading a large file .read() may return null, having consumed all buffered content so far, but there is still more data to come not yet buffered. In this case a new 'readable' event will be emitted when there is more data in the buffer. Finally the 'end' event will be emitted when there is no more data to come.
Therefore to read a file's whole contents from a readable, it is necessary to collect chunks across multiple 'readable' events:
const chunks = []; readable.on('readable', () => { let chunk; while (null !== (chunk = readable.read())) { chunks.push(chunk); } }); readable.on('end', () => { const content = chunks.join(''); });
A Readable stream in object mode will always return a single item from a call to readable.read(size), regardless of the value of the size argument.
If the readable.read() method returns a chunk of data, a 'data' event will also be emitted.
Calling read after the 'end' event has been emitted will return null. No runtime error will be raised.
@param size
Optional argument to specify how much data to read.
reduce<T>(
fn: (previous: any, data: any, options?: Abortable) => T
): Promise<T>;
This method calls fn on each chunk of the stream in order, passing it the result from the calculation on the previous element. It returns a promise for the final value of the reduction.
If no initial value is supplied the first chunk of the stream is used as the initial value. If the stream is empty, the promise is rejected with a TypeError with the ERR_INVALID_ARGS code property.
The reducer function iterates the stream element-by-element which means that there is no concurrency parameter or parallelism. To perform a reduce concurrently, you can extract the async function to readable.map method.
@param fn
a reducer function to call over every chunk in the stream. Async or not.
@returns
a promise for the final value of the reduction.
reduce<T>(
fn: (previous: T, data: any, options?: Abortable) => T,
initial: T,
options?: Abortable
): Promise<T>;
This method calls fn on each chunk of the stream in order, passing it the result from the calculation on the previous element. It returns a promise for the final value of the reduction.
If no initial value is supplied the first chunk of the stream is used as the initial value. If the stream is empty, the promise is rejected with a TypeError with the ERR_INVALID_ARGS code property.
The reducer function iterates the stream element-by-element which means that there is no concurrency parameter or parallelism. To perform a reduce concurrently, you can extract the async function to readable.map method.
@param fn
a reducer function to call over every chunk in the stream. Async or not.
@param initial
the initial value to use in the reduction.
@returns
a promise for the final value of the reduction.
ref(): this;
Opposite of unref(), calling ref() on a previously unrefed socket will not let the program exit if it's the only socket left (the default behavior). If the socket is refed calling ref again will have no effect.
@returns
The socket itself.
removeAllListeners<E extends keyof SocketEventMap>(
eventName?: E
): this;
Removes all listeners, or those of the specified eventName.
It is bad practice to remove listeners added elsewhere in the code, particularly when the EventEmitter instance was created by some other component or module (e.g. sockets or file streams).
Returns a reference to the EventEmitter, so that calls can be chained.
removeAllListeners(
eventName?: string | symbol
): this;
removeListener<E extends keyof SocketEventMap>(
eventName: E,
listener: (...args: SocketEventMap[E]) => void
): this;
Removes the specified listener from the listener array for the event named eventName.
const callback = (stream) => { console.log('someone connected!'); }; server.on('connection', callback); // ... server.removeListener('connection', callback);
removeListener() will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified eventName, then removeListener() must be called multiple times to remove each instance.
Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution will not remove them from emit() in progress. Subsequent events behave as expected.
import { EventEmitter } from 'node:events'; class MyEmitter extends EventEmitter {} const myEmitter = new MyEmitter(); const callbackA = () => { console.log('A'); myEmitter.removeListener('event', callbackB); }; const callbackB = () => { console.log('B'); }; myEmitter.on('event', callbackA); myEmitter.on('event', callbackB); // callbackA removes listener callbackB but it will still be called. // Internal listener array at time of emit [callbackA, callbackB] myEmitter.emit('event'); // Prints: // A // B // callbackB is now removed. // Internal listener array [callbackA] myEmitter.emit('event'); // Prints: // A
Because listeners are managed using an internal array, calling this will change the position indexes of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the emitter.listeners() method will need to be recreated.
When a single function has been added as a handler multiple times for a single event (as in the example below), removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:
import { EventEmitter } from 'node:events'; const ee = new EventEmitter(); function pong() { console.log('pong'); } ee.on('ping', pong); ee.once('ping', pong); ee.removeListener('ping', pong); ee.emit('ping'); ee.emit('ping');
Returns a reference to the EventEmitter, so that calls can be chained.
removeListener(
eventName: string | symbol,
listener: (...args: any[]) => void
): this;
resetAndDestroy(): this;
Close the TCP connection by sending an RST packet and destroy the stream. If this TCP socket is in connecting status, it will send an RST packet and destroy this TCP socket once it is connected. Otherwise, it will call socket.destroy with an ERR_SOCKET_CLOSED Error. If this is not a TCP socket (for example, a pipe), calling this method will immediately throw an ERR_INVALID_HANDLE_TYPE Error.
resume(): this;
Resumes reading after a call to socket.pause().
@returns
The socket itself.
setDefaultEncoding(
encoding: BufferEncoding
): this;
The writable.setDefaultEncoding() method sets the default encoding for a Writable stream.
@param encoding
The new default encoding
setEncoding(
encoding?: BufferEncoding
): this;
Set the encoding for the socket as a Readable Stream. See readable.setEncoding() for more information.
@returns
The socket itself.
setKeepAlive(
options: SetKeepAliveOptions
): this;
Configure keep-alive using an options object. See socket.setKeepAlive() for a description of each property.
socket.setKeepAlive({ enable: true, initialDelay: 1000, interval: 1000, count: 10 });
@returns
The socket itself.
setKeepAlive(
enable?: boolean,
initialDelay?: number,
interval?: number,
count?: number
): this;
Configure keep-alive using positional arguments. See socket.setKeepAlive() for a description of each argument.
@param enable
Default: false
@param initialDelay
Default: 0
@param interval
Default: 1000
@param count
Default: 10
@returns
The socket itself.
setMaxListeners(
n: number
): this;
By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default that helps finding memory leaks. The emitter.setMaxListeners() method allows the limit to be modified for this specific EventEmitter instance. The value can be set to Infinity (or 0) to indicate an unlimited number of listeners.
Returns a reference to the EventEmitter, so that calls can be chained.
setNoDelay(
noDelay?: boolean
): this;
Enable/disable the use of Nagle's algorithm.
When a TCP connection is created, it will have Nagle's algorithm enabled.
Nagle's algorithm delays data before it is sent via the network. It attempts to optimize throughput at the expense of latency.
Passing true for noDelay or not passing an argument will disable Nagle's algorithm for the socket. Passing false for noDelay will enable Nagle's algorithm.
@returns
The socket itself.
setTimeout(
timeout: number,
callback?: () => void
): this;
Sets the socket to timeout after timeout milliseconds of inactivity on the socket. By default net.Socket do not have a timeout.
When an idle timeout is triggered the socket will receive a 'timeout' event but the connection will not be severed. The user must manually call socket.end() or socket.destroy() to end the connection.
socket.setTimeout(3000); socket.on('timeout', () => { console.log('socket timeout'); socket.end(); });
If timeout is 0, then the existing idle timeout is disabled.
The optional callback parameter will be added as a one-time listener for the 'timeout' event.
@returns
The socket itself.
setTypeOfService(
tos: number
): this;
Sets the Type of Service (TOS) field for IPv4 packets or Traffic Class for IPv6 Packets sent from this socket. This can be used to prioritize network traffic.
setTypeOfService() may be called before the socket is connected; the value will be cached and applied when the socket establishes a connection. getTypeOfService() will return the currently set value even before connection.
On some platforms (e.g., Linux), certain TOS/ECN bits may be masked or ignored, and behavior can differ between IPv4 and IPv6 or dual-stack sockets. Callers should verify platform-specific semantics.
@param tos
The TOS value to set (0-255).
@returns
The socket itself.
some(
fn: (data: any, options?: Abortable) => boolean | Promise<boolean>,
options?: Pick<ReadableOperatorOptions, 'signal' | 'concurrency'>
): Promise<boolean>;
This method is similar to Array.prototype.some and calls fn on each chunk in the stream until the awaited return value is true (or any truthy value). Once an fn call on a chunk awaited return value is truthy, the stream is destroyed and the promise is fulfilled with true. If none of the fn calls on the chunks return a truthy value, the promise is fulfilled with false.
@param fn
a function to call on each chunk of the stream. Async or not.
@returns
a promise evaluating to true if fn returned a truthy value for at least one of the chunks.
take(
limit: number,
options?: Abortable
): Readable;
This method returns a new stream with the first limit chunks.
@param limit
the number of chunks to take from the readable.
@returns
a stream with limit chunks taken.
toArray(
options?: Abortable
): Promise<any[]>;
This method allows easily obtaining the contents of a stream.
As this method reads the entire stream into memory, it negates the benefits of streams. It's intended for interoperability and convenience, not as the primary way to consume streams.
@returns
a promise containing an array with the contents of the stream.
uncork(): void;
The writable.uncork() method flushes all data buffered since cork was called.
When using writable.cork() and writable.uncork() to manage the buffering of writes to a stream, defer calls to writable.uncork() using process.nextTick(). Doing so allows batching of all writable.write() calls that occur within a given Node.js event loop phase.
stream.cork(); stream.write('some '); stream.write('data '); process.nextTick(() => stream.uncork());
If the writable.cork() method is called multiple times on a stream, the same number of calls to writable.uncork() must be called to flush the buffered data.
stream.cork(); stream.write('some '); stream.cork(); stream.write('data '); process.nextTick(() => { stream.uncork(); // The data will not be flushed until uncork() is called a second time. stream.uncork(); });
See also: writable.cork().

unpipe(

destination?: WritableStream

): this;

The readable.unpipe() method detaches a Writable stream previously attached using the pipe method.

If the destination is not specified, then all pipes are detached.

If the destination is specified, but no pipe is set up for it, then the method does nothing.

import fs from 'node:fs';
const readable = getReadableStreamSomehow();
const writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt',
// but only for the first second.
readable.pipe(writable);
setTimeout(() => {
  console.log('Stop writing to file.txt.');
  readable.unpipe(writable);
  console.log('Manually close the file stream.');
  writable.end();
}, 1000);

@param destination

Optional specific stream to unpipe

unref(): this;
Calling unref() on a socket will allow the program to exit if this is the only active socket in the event system. If the socket is already unrefed callingunref() again will have no effect.
@returns
The socket itself.
unshift(
chunk: any,
encoding?: BufferEncoding
): void;
Passing chunk as null signals the end of the stream (EOF) and behaves the same as readable.push(null), after which no more data can be written. The EOF signal is put at the end of the buffer and any buffered data will still be flushed.
The readable.unshift() method pushes a chunk of data back into the internal buffer. This is useful in certain situations where a stream is being consumed by code that needs to "un-consume" some amount of data that it has optimistically pulled out of the source, so that the data can be passed on to some other party.
The stream.unshift(chunk) method cannot be called after the 'end' event has been emitted or a runtime error will be thrown.
Developers using stream.unshift() often should consider switching to use of a Transform stream instead. See the API for stream implementers section for more information.
// Pull off a header delimited by \n\n. // Use unshift() if we get too much. // Call the callback with (error, header, stream). import { StringDecoder } from 'node:string_decoder'; function parseHeader(stream, callback) { stream.on('error', callback); stream.on('readable', onReadable); const decoder = new StringDecoder('utf8'); let header = ''; function onReadable() { let chunk; while (null !== (chunk = stream.read())) { const str = decoder.write(chunk); if (str.includes('\n\n')) { // Found the header boundary. const split = str.split(/\n\n/); header += split.shift(); const remaining = split.join('\n\n'); const buf = Buffer.from(remaining, 'utf8'); stream.removeListener('error', callback); // Remove the 'readable' listener before unshifting. stream.removeListener('readable', onReadable); if (buf.length) stream.unshift(buf); // Now the body of the message can be read from the stream. callback(null, header, stream); return; } // Still reading the header. header += str; } } }
Unlike push, stream.unshift(chunk) will not end the reading process by resetting the internal reading state of the stream. This can cause unexpected results if readable.unshift() is called during a read (i.e. from within a _read implementation on a custom stream). Following the call to readable.unshift() with an immediate push will reset the reading state appropriately, however it is best to simply avoid calling readable.unshift() while in the process of performing a read.
@param chunk
Chunk of data to unshift onto the read queue. For streams not operating in object mode, chunk must be a {string}, {Buffer}, {TypedArray}, {DataView} or null. For object mode streams, chunk may be any JavaScript value.
@param encoding
Encoding of string chunks. Must be a valid Buffer encoding, such as 'utf8' or 'ascii'.
wrap(
stream: ReadableStream
): this;
Prior to Node.js 0.10, streams did not implement the entire node:stream module API as it is currently defined. (See Compatibility for more information.)
When using an older Node.js library that emits 'data' events and has a pause method that is advisory only, the readable.wrap() method can be used to create a Readable stream that uses the old stream as its data source.
It will rarely be necessary to use readable.wrap() but the method has been provided as a convenience for interacting with older Node.js applications and libraries.
import { OldReader } from './old-api-module.js'; import { Readable } from 'node:stream'; const oreader = new OldReader(); const myReader = new Readable().wrap(oreader); myReader.on('readable', () => { myReader.read(); // etc. });
@param stream
An "old style" readable stream
write(
buffer: string | Uint8Array<ArrayBufferLike>,
cb?: (err?: null | Error) => void
): boolean;
Sends data on the socket. The second parameter specifies the encoding in the case of a string. It defaults to UTF8 encoding.
Returns true if the entire data was flushed successfully to the kernel buffer. Returns false if all or part of the data was queued in user memory.'drain' will be emitted when the buffer is again free.
The optional callback parameter will be executed when the data is finally written out, which may not be immediately.
See Writable stream write() method for more information.
write(
str: string | Uint8Array<ArrayBufferLike>,
encoding?: BufferEncoding,
cb?: (err?: null | Error) => void
): boolean;
Sends data on the socket, with an explicit encoding for string data.
@param encoding
Only used when data is string.
static from(
src: string | Blob | Promise<any> | ReadableStream | WritableStream | Iterable<any, any, any> | AsyncIterable<any, any, any> | (source: AsyncIterable<any>) => AsyncIterable<any> | (source: AsyncIterable<any>) => Promise<void> | ReadableWritablePair<any, any> | ReadableStream<any> | WritableStream<any>
): Duplex;
A utility method for creating duplex streams.
Stream converts writable stream into writable Duplex and readable stream to Duplex.
Blob converts into readable Duplex.
string converts into readable Duplex.
ArrayBuffer converts into readable Duplex.
AsyncIterable converts into a readable Duplex. Cannot yield null.
AsyncGeneratorFunction converts into a readable/writable transform Duplex. Must take a source AsyncIterable as first parameter. Cannot yield null.
AsyncFunction converts into a writable Duplex. Must return either null or undefined
Object ({ writable, readable }) converts readable and writable into Stream and then combines them into Duplex where the Duplex will write to the writable and read from the readable.
Promise converts into readable Duplex. Value null is ignored.
static fromWeb(
duplexStream: ReadableWritablePair,
options?: Pick<DuplexOptions<Duplex>, 'allowHalfOpen' | 'decodeStrings' | 'encoding' | 'highWaterMark' | 'objectMode' | 'signal'>
): Duplex;
A utility method for creating a Duplex from a web ReadableStream and WritableStream.
static toWeb(
streamDuplex: ReadWriteStream,
options?: DuplexToWebOptions
): ReadableWritablePair;
A utility method for creating a web ReadableStream and WritableStream from a Duplex.

worker_threads.Transferable

Referenced types

class ArrayBuffer

interface MessagePort

class AbortSignal

interface FileHandle

interface ReadableStream<R = any>

interface WritableStream<W = any>

interface TransformStream<I = any, O = any>

class Server

class Socket