ClientRequest.constructor constructor | Node.js http module | Bun

ClientRequest.constructor constructor | Node.js http module | BunBuildDocsReferenceGuidesBlogDiscord/node:http/ClientRequest/constructorCoconstructor

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constructor

http.ClientRequest.constructorNot implemented in Bun

constructor ClientRequest(url: string | URL | ClientRequestArgs,cb?: (res: IncomingMessage) => void): ClientRequest;Referenced typesinterface URLhash: stringhost: stringhostname: stringhref: stringreadonly origin: stringpassword: stringpathname: stringport: stringprotocol: stringsearch: stringreadonly searchParams: URLSearchParamsusername: stringtoJSON(): string;interface ClientRequestArgs_defaultAgent?: Agentagent?: boolean | Agentauth?: null | stringcreateConnection?: (options: ClientRequestArgs, oncreate: (err: null | Error, socket: Duplex) => void) => undefined | null | DuplexdefaultPort?: string | numberfamily?: numberheaders?: readonly string[] | OutgoingHttpHeadershints?: numberOne or more supported getaddrinfo flags. Multiple flags may be passed by bitwise ORing their values.

host?: null | stringhostname?: null | stringinsecureHTTPParser?: booleanjoinDuplicateHeaders?: booleanlocalAddress?: stringlocalPort?: numberlookup?: LookupFunctionmaxHeaderSize?: numbermethod?: stringpath?: null | stringport?: null | string | numberprotocol?: null | stringsetDefaultHeaders?: booleansetHost?: booleansignal?: AbortSignalsocketPath?: stringtimeout?: numberuniqueHeaders?: string | string[][]class ClientRequestThis object is created internally and returned from request. It represents an in-progress request whose header has already been queued. The header is still mutable using the setHeader(name, value), getHeader(name), removeHeader(name) API. The actual header will be sent along with the first data chunk or when calling request.end().

To get the response, add a listener for 'response' to the request object. 'response' will be emitted from the request object when the response headers have been received. The 'response' event is executed with one argument which is an instance of IncomingMessage.

During the 'response' event, one can add listeners to the response object; particularly to listen for the 'data' event.

If no 'response' handler is added, then the response will be entirely discarded. However, if a 'response' event handler is added, then the data from the response object must be consumed, either by calling response.read() whenever there is a 'readable' event, or by adding a 'data' handler, or by calling the .resume() method. Until the data is consumed, the 'end' event will not fire. Also, until the data is read it will consume memory that can eventually lead to a 'process out of memory' error.

For backward compatibility, res will only emit 'error' if there is an 'error' listener registered.

Set Content-Length header to limit the response body size. If response.strictContentLength is set to true, mismatching the Content-Length header value will result in an Error being thrown, identified by code:``'ERR_HTTP_CONTENT_LENGTH_MISMATCH'.

Content-Length value should be in bytes, not characters. Use Buffer.byteLength() to determine the length of the body in bytes.

chunkedEncoding: booleanreadonly closed: booleanIs true after 'close' has been emitted.

destroyed: booleanIs true after writable.destroy() has been called.

readonly errored: null | ErrorReturns error if the stream has been destroyed with an error.

readonly headersSent: booleanRead-only. true if the headers were sent, otherwise false.

host: stringThe request host.

maxHeadersCount: numberLimits maximum response headers count. If set to 0, no limit will be applied.

method: stringThe request method.

path: stringThe request path.

protocol: stringThe request protocol.

readonly req: IncomingMessage { res.write('hello\n'); res.end(); }) .listen(3000); setInterval(() => { // Adapting a keep-alive agent http.get('http://localhost:3000', { agent }, (res) => { res.on('data', (data) => { // Do nothing }); }); }, 5000); // Sending request on 5s interval so it's easy to hit idle timeout ``` By marking a request whether it reused socket or not, we can do automatic error retry base on it. ```js import http from 'node:http'; const agent = new http.Agent({ keepAlive: true }); function retriableRequest() { const req = http .get('http://localhost:3000', { agent }, (res) => { // ... }) .on('error', (err) => { // Check if retry is needed if (req.reusedSocket && err.code === 'ECONNRESET') { retriableRequest(); } }); } retriableRequest(); ```" data-algolia-static="false" data-algolia-merged="false" data-type="Property">reusedSocket: booleanWhen sending request through a keep-alive enabled agent, the underlying socket might be reused. But if server closes connection at unfortunate time, client may run into a 'ECONNRESET' error.

import http from 'node:http'; const agent = new http.Agent({ keepAlive: true }); // Server has a 5 seconds keep-alive timeout by default http .createServer((req, res) => { res.write('hello\n'); res.end(); }) .listen(3000); setInterval(() => { // Adapting a keep-alive agent http.get('http://localhost:3000', { agent }, (res) => { res.on('data', (data) => { // Do nothing }); }); }, 5000); // Sending request on 5s interval so it's easy to hit idle timeout By marking a request whether it reused socket or not, we can do automatic error retry base on it.

import http from 'node:http'; const agent = new http.Agent({ keepAlive: true }); function retriableRequest() { const req = http .get('http://localhost:3000', { agent }, (res) => { // ... }) .on('error', (err) => { // Check if retry is needed if (req.reusedSocket && err.code === 'ECONNRESET') { retriableRequest(); } }); } retriableRequest(); sendDate: booleanshouldKeepAlive: booleanreadonly socket: null | SocketReference to the underlying socket. Usually, users will not want to access this property.

After calling outgoingMessage.end(), this property will be nulled.

useChunkedEncodingByDefault: booleanwritable: booleanIs true if it is safe to call writable.write(), which means the stream has not been destroyed, errored, or ended.

readonly writableAborted: booleanReturns whether the stream was destroyed or errored before emitting 'finish'.

readonly writableCorked: numberNumber of times writable.uncork() needs to be called in order to fully uncork the stream.

readonly writableEnded: booleanIs 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: booleanIs set to true immediately before the 'finish' event is emitted.

readonly writableHighWaterMark: numberReturn the value of highWaterMark passed when creating this Writable.

readonly writableLength: numberThis 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: booleanIs true if the stream's buffer has been full and stream will emit 'drain'.

readonly writableObjectMode: booleanGetter 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;_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](): Promisevoid>;Calls writable.destroy() with an AbortError and returns a promise that fulfills when the stream is finished.

[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. } } addListenerE extends keyof ClientRequestEventMap>(eventName: E,listener: (...args: ClientRequestEventMap[E]) => void): this;Alias for emitter.on(eventName, listener).

addListener(eventName: string | symbol,listener: (...args: any[]) => void): this;addTrailers(headers: OutgoingHttpHeaders | readonly [string, string][]): void;Adds HTTP trailers (headers but at the end of the message) to the message.

Trailers will only be emitted if the message is chunked encoded. If not, the trailers will be silently discarded.

HTTP requires the Trailer header to be sent to emit trailers, with a list of header field names in its value, e.g.

message.writeHead(200, { 'Content-Type': 'text/plain', 'Trailer': 'Content-MD5' }); message.write(fileData); message.addTrailers({ 'Content-MD5': '7895bf4b8828b55ceaf47747b4bca667' }); message.end(); Attempting to set a header field name or value that contains invalid characters will result in a TypeError being thrown.

appendHeader(name: string,value: string | readonly string[]): this;Append a single header value to the header object.

If the value is an array, this is equivalent to calling this method multiple times.

If there were no previous values for the header, this is equivalent to calling outgoingMessage.setHeader(name, value).

Depending of the value of options.uniqueHeaders when the client request or the server were created, this will end up in the header being sent multiple times or a single time with values joined using ; .

@param nameHeader name

@param valueHeader value

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 writable stream has ended and subsequent calls to write() or end() will result in an ERR_STREAM_DESTROYED error. This is a destructive and immediate way to destroy a stream. Previous calls to write() may not have drained, and may trigger an ERR_STREAM_DESTROYED error. Use end() instead of destroy if data should flush before close, or wait for the 'drain' event before destroying the stream.

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 writable._destroy().

@param errorOptional, an error to emit with 'error' event.

emitE extends keyof ClientRequestEventMap>(eventName: E,...args: ClientRequestEventMap[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(cb?: () => void): this;Calling the writable.end() method signals that no more data will be written to the Writable. The optional chunk and encoding arguments allow one final additional chunk of data to be written immediately before closing the stream.

Calling the write method after calling end will raise an error.

// Write 'hello, ' and then end with 'world!'. import fs from 'node:fs'; const file = fs.createWriteStream('example.txt'); file.write('hello, '); file.end('world!'); // Writing more now is not allowed! end(chunk: any,cb?: () => void): this;Calling the writable.end() method signals that no more data will be written to the Writable. The optional chunk and encoding arguments allow one final additional chunk of data to be written immediately before closing the stream.

Calling the write method after calling end will raise an error.

// Write 'hello, ' and then end with 'world!'. import fs from 'node:fs'; const file = fs.createWriteStream('example.txt'); file.write('hello, '); file.end('world!'); // Writing more now is not allowed! @param chunkOptional data to write. For streams not operating in object mode, chunk must be a {string}, {Buffer}, {TypedArray} or {DataView}. For object mode streams, chunk may be any JavaScript value other than null.

end(chunk: any,encoding: BufferEncoding,cb?: () => void): this;Calling the writable.end() method signals that no more data will be written to the Writable. The optional chunk and encoding arguments allow one final additional chunk of data to be written immediately before closing the stream.

Calling the write method after calling end will raise an error.

// Write 'hello, ' and then end with 'world!'. import fs from 'node:fs'; const file = fs.createWriteStream('example.txt'); file.write('hello, '); file.end('world!'); // Writing more now is not allowed! @param chunkOptional data to write. For streams not operating in object mode, chunk must be a {string}, {Buffer}, {TypedArray} or {DataView}. For object mode streams, chunk may be any JavaScript value other than null.

@param encodingThe encoding if chunk is a string

{}); myEE.on('bar', () => {}); const sym = Symbol('symbol'); myEE.on(sym, () => {}); console.log(myEE.eventNames()); // Prints: [ 'foo', 'bar', Symbol(symbol) ] ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">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) ] flushHeaders(): void;Flushes the message headers.

For efficiency reason, Node.js normally buffers the message headers until outgoingMessage.end() is called or the first chunk of message data is written. It then tries to pack the headers and data into a single TCP packet.

It is usually desired (it saves a TCP round-trip), but not when the first data is not sent until possibly much later. outgoingMessage.flushHeaders() bypasses the optimization and kickstarts the message.

getHeader(name: string): undefined | string | number | string[];Gets the value of the HTTP header with the given name. If that header is not set, the returned value will be undefined.

@param nameName of header

getHeaderNames(): string[];Returns an array containing the unique names of the current outgoing headers. All names are lowercase.

getHeaders(): OutgoingHttpHeaders;Returns a shallow copy of the current outgoing headers. Since a shallow copy is used, array values may be mutated without additional calls to various header-related HTTP module methods. The keys of the returned object are the header names and the values are the respective header values. All header names are lowercase.

The object returned by the outgoingMessage.getHeaders() method does not prototypically inherit from the JavaScript Object. This means that typical Object methods such as obj.toString(), obj.hasOwnProperty(), and others are not defined and will not work.

outgoingMessage.setHeader('Foo', 'bar'); outgoingMessage.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']); const headers = outgoingMessage.getHeaders(); // headers === { foo: 'bar', 'set-cookie': ['foo=bar', 'bar=baz'] } getMaxListeners(): number;Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to events.defaultMaxListeners.

getRawHeaderNames(): string[];Returns an array containing the unique names of the current outgoing raw headers. Header names are returned with their exact casing being set.

request.setHeader('Foo', 'bar'); request.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']); const headerNames = request.getRawHeaderNames(); // headerNames === ['Foo', 'Set-Cookie'] hasHeader(name: string): boolean;Returns true if the header identified by name is currently set in the outgoing headers. The header name is case-insensitive.

const hasContentType = outgoingMessage.hasHeader('content-type'); listenerCountE extends keyof ClientRequestEventMap>(eventName: E,listener?: (...args: ClientRequestEventMap[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 eventNameThe name of the event being listened for

@param listenerThe event handler function

listenerCount(eventName: string | symbol,listener?: (...args: any[]) => void): number; { console.log('someone connected!'); }); console.log(util.inspect(server.listeners('connection'))); // Prints: [ [Function] ] ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">listenersE extends keyof ClientRequestEventMap>(eventName: E): (...args: ClientRequestEventMap[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[];offE extends keyof ClientRequestEventMap>(eventName: E,listener: (...args: ClientRequestEventMap[E]) => void): this;Alias for emitter.removeListener().

off(eventName: string | symbol,listener: (...args: any[]) => void): this; { 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. ```js 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 ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">onE extends keyof ClientRequestEventMap>(eventName: E,listener: (...args: ClientRequestEventMap[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 eventNameThe name of the event.

@param listenerThe callback function

on(eventName: string | symbol,listener: (...args: any[]) => void): this; { 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. ```js 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 ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">onceE extends keyof ClientRequestEventMap>(eventName: E,listener: (...args: ClientRequestEventMap[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 eventNameThe name of the event.

@param listenerThe callback function

once(eventName: string | symbol,listener: (...args: any[]) => void): this;onSocket(socket: Socket): void;pipeT extends WritableStream>(destination: T,options?: PipeOptions): T; { console.log('someone connected!'); }); ``` Returns a reference to the `EventEmitter`, so that calls can be chained." data-algolia-static="false" data-algolia-merged="false" data-type="Method">prependListenerE extends keyof ClientRequestEventMap>(eventName: E,listener: (...args: ClientRequestEventMap[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 eventNameThe name of the event.

@param listenerThe callback function

prependListener(eventName: string | symbol,listener: (...args: any[]) => void): this; { console.log('Ah, we have our first user!'); }); ``` Returns a reference to the `EventEmitter`, so that calls can be chained." data-algolia-static="false" data-algolia-merged="false" data-type="Method">prependOnceListenerE extends keyof ClientRequestEventMap>(eventName: E,listener: (...args: ClientRequestEventMap[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 eventNameThe name of the event.

@param listenerThe callback function

prependOnceListener(eventName: string | symbol,listener: (...args: any[]) => void): this; 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'); ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">rawListenersE extends keyof ClientRequestEventMap>(eventName: E): (...args: ClientRequestEventMap[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[];removeAllListenersE extends keyof ClientRequestEventMap>(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;removeHeader(name: string): void;Removes a header that is queued for implicit sending.

outgoingMessage.removeHeader('Content-Encoding'); @param nameHeader name

{ 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. ```js 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: ```js 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." data-algolia-static="false" data-algolia-merged="false" data-type="Method">removeListenerE extends keyof ClientRequestEventMap>(eventName: E,listener: (...args: ClientRequestEventMap[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;setDefaultEncoding(encoding: BufferEncoding): this;The writable.setDefaultEncoding() method sets the default encoding for a Writable stream.

@param encodingThe new default encoding

setHeader(name: string,value: string | number | readonly string[]): this;Sets a single header value. If the header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings to send multiple headers with the same name.

@param nameHeader name

@param valueHeader value

{ const headers = new Headers({ 'Content-Type': 'text/html' }); res.setHeaders(headers); res.writeHead(200, { 'Content-Type': 'text/plain' }); res.end('ok'); }); ```" data-algolia-static="false" data-algolia-merged="false" data-type="Method">setHeaders(headers: Headers | Mapstring, string | number | readonly string[]>): this;Sets multiple header values for implicit headers. headers must be an instance of Headers or Map, if a header already exists in the to-be-sent headers, its value will be replaced.

const headers = new Headers({ foo: 'bar' }); outgoingMessage.setHeaders(headers); or

const headers = new Map([['foo', 'bar']]); outgoingMessage.setHeaders(headers); When headers have been set with outgoingMessage.setHeaders(), they will be merged with any headers passed to response.writeHead(), with the headers passed to response.writeHead() given precedence.

// Returns content-type = text/plain const server = http.createServer((req, res) => { const headers = new Headers({ 'Content-Type': 'text/html' }); res.setHeaders(headers); res.writeHead(200, { 'Content-Type': 'text/plain' }); res.end('ok'); }); 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): void;Once a socket is assigned to this request and is connected socket.setNoDelay() will be called.

setSocketKeepAlive(enable?: boolean,initialDelay?: number): void;Once a socket is assigned to this request and is connected socket.setKeepAlive() will be called.

setTimeout(timeout: number,callback?: () => void): this;Once a socket is assigned to this request and is connected socket.setTimeout() will be called.

@param timeoutMilliseconds before a request times out.

@param callbackOptional function to be called when a timeout occurs. Same as binding to the 'timeout' event.

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. ```js 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()`." data-algolia-static="false" data-algolia-merged="false" data-type="Method">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().

{ console.log('Write completed, do more writes now.'); }); ``` A `Writable` stream in object mode will always ignore the `encoding` argument." data-algolia-static="false" data-algolia-merged="false" data-type="Method">write(chunk: any,callback?: (error: undefined | null | Error) => void): boolean;The writable.write() method writes some data to the stream, and calls the supplied callback once the data has been fully handled. If an error occurs, the callback will be called with the error as its first argument. The callback is called asynchronously and before 'error' is emitted.

The return value is true if the internal buffer is less than the highWaterMark configured when the stream was created after admitting chunk. If false is returned, further attempts to write data to the stream should stop until the 'drain' event is emitted.

While a stream is not draining, calls to write() will buffer chunk, and return false. Once all currently buffered chunks are drained (accepted for delivery by the operating system), the 'drain' event will be emitted. Once write() returns false, do not write more chunks until the 'drain' event is emitted. While calling write() on a stream that is not draining is allowed, Node.js will buffer all written chunks until maximum memory usage occurs, at which point it will abort unconditionally. Even before it aborts, high memory usage will cause poor garbage collector performance and high RSS (which is not typically released back to the system, even after the memory is no longer required). Since TCP sockets may never drain if the remote peer does not read the data, writing a socket that is not draining may lead to a remotely exploitable vulnerability.

Writing data while the stream is not draining is particularly problematic for a Transform, because the Transform streams are paused by default until they are piped or a 'data' or 'readable' event handler is added.

If the data to be written can be generated or fetched on demand, it is recommended to encapsulate the logic into a Readable and use pipe. However, if calling write() is preferred, it is possible to respect backpressure and avoid memory issues using the 'drain' event:

function write(data, cb) { if (!stream.write(data)) { stream.once('drain', cb); } else { process.nextTick(cb); } } // Wait for cb to be called before doing any other write. write('hello', () => { console.log('Write completed, do more writes now.'); }); A Writable stream in object mode will always ignore the encoding argument.

@param chunkOptional data to write. For streams not operating in object mode, chunk must be a {string}, {Buffer}, {TypedArray} or {DataView}. For object mode streams, chunk may be any JavaScript value other than null.

@param callbackCallback for when this chunk of data is flushed.

@returnsfalse if the stream wishes for the calling code to wait for the 'drain' event to be emitted before continuing to write additional data; otherwise true.

write(chunk: any,encoding: BufferEncoding,callback?: (error: undefined | null | Error) => void): boolean;The writable.write() method writes some data to the stream, and calls the supplied callback once the data has been fully handled. If an error occurs, the callback will be called with the error as its first argument. The callback is called asynchronously and before 'error' is emitted.

The return value is true if the internal buffer is less than the highWaterMark configured when the stream was created after admitting chunk. If false is returned, further attempts to write data to the stream should stop until the 'drain' event is emitted.

While a stream is not draining, calls to write() will buffer chunk, and return false. Once all currently buffered chunks are drained (accepted for delivery by the operating system), the 'drain' event will be emitted. Once write() returns false, do not write more chunks until the 'drain' event is emitted. While calling write() on a stream that is not draining is allowed, Node.js will buffer all written chunks until maximum memory usage occurs, at which point it will abort unconditionally. Even before it aborts, high memory usage will cause poor garbage collector performance and high RSS (which is not typically released back to the system, even after the memory is no longer required). Since TCP sockets may never drain if the remote peer does not read the data, writing a socket that is not draining may lead to a remotely exploitable vulnerability.

Writing data while the stream is not draining is particularly problematic for a Transform, because the Transform streams are paused by default until they are piped or a 'data' or 'readable' event handler is added.

If the data to be written can be generated or fetched on demand, it is recommended to encapsulate the logic into a Readable and use pipe. However, if calling write() is preferred, it is possible to respect backpressure and avoid memory issues using the 'drain' event:

function write(data, cb) { if (!stream.write(data)) { stream.once('drain', cb); } else { process.nextTick(cb); } } // Wait for cb to be called before doing any other write. write('hello', () => { console.log('Write completed, do more writes now.'); }); A Writable stream in object mode will always ignore the encoding argument.

@param chunkOptional data to write. For streams not operating in object mode, chunk must be a {string}, {Buffer}, {TypedArray} or {DataView}. For object mode streams, chunk may be any JavaScript value other than null.

@param encodingThe encoding, if chunk is a string.

@param callbackCallback for when this chunk of data is flushed.

@returnsfalse if the stream wishes for the calling code to wait for the 'drain' event to be emitted before continuing to write additional data; otherwise true.

static fromWeb(writableStream: WritableStream,options?: PickWritableOptionsWritable>, 'signal' | 'decodeStrings' | 'highWaterMark' | 'objectMode'>): Writable;A utility method for creating a Writable from a web WritableStream.

static toWeb(streamWritable: WritableStream): WritableStream;A utility method for creating a web WritableStream from a Writable.

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