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Class: LogToEvTransport

logging/custom_transport.LogToEvTransport

Hierarchy

  • TransportStream

    LogToEvTransport

Constructors

constructor

new LogToEvTransport(opts?)

Parameters

NameType
opts?any

Overrides

TransportStream.constructor

Properties

closed

Readonly closed: boolean

Is true after 'close' has been emitted.

Since

v8.0.0

Inherited from

TransportStream.closed


destroyed

destroyed: boolean

Is true after writable.destroy() has been called.

Since

v8.0.0

Inherited from

TransportStream.destroyed


errored

Readonly errored: Error

Returns error if the stream has been destroyed with an error.

Since

v18.0.0

Inherited from

TransportStream.errored


format

Optional format: Format

Inherited from

TransportStream.format


handleExceptions

Optional handleExceptions: boolean

Inherited from

TransportStream.handleExceptions


handleRejections

Optional handleRejections: boolean

Inherited from

TransportStream.handleRejections


level

Optional level: string

Inherited from

TransportStream.level


silent

Optional silent: boolean

Inherited from

TransportStream.silent


writable

Readonly writable: boolean

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

Since

v11.4.0

Inherited from

TransportStream.writable


writableCorked

Readonly writableCorked: number

Number of times writable.uncork() needs to be called in order to fully uncork the stream.

Since

v13.2.0, v12.16.0

Inherited from

TransportStream.writableCorked


writableEnded

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.

Since

v12.9.0

Inherited from

TransportStream.writableEnded


writableFinished

Readonly writableFinished: boolean

Is set to true immediately before the 'finish' event is emitted.

Since

v12.6.0

Inherited from

TransportStream.writableFinished


writableHighWaterMark

Readonly writableHighWaterMark: number

Return the value of highWaterMark passed when creating this Writable.

Since

v9.3.0

Inherited from

TransportStream.writableHighWaterMark


writableLength

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.

Since

v9.4.0

Inherited from

TransportStream.writableLength


writableNeedDrain

Readonly writableNeedDrain: boolean

Is true if the stream's buffer has been full and stream will emit 'drain'.

Since

v15.2.0, v14.17.0

Inherited from

TransportStream.writableNeedDrain


writableObjectMode

Readonly writableObjectMode: boolean

Getter for the property objectMode of a given Writable stream.

Since

v12.3.0

Inherited from

TransportStream.writableObjectMode


captureRejectionSymbol

Static Readonly captureRejectionSymbol: typeof captureRejectionSymbol

Inherited from

TransportStream.captureRejectionSymbol


captureRejections

Static captureRejections: boolean

Sets or gets the default captureRejection value for all emitters.

Inherited from

TransportStream.captureRejections


defaultMaxListeners

Static defaultMaxListeners: number

Inherited from

TransportStream.defaultMaxListeners


errorMonitor

Static Readonly errorMonitor: typeof errorMonitor

This symbol shall be used to install a listener for only monitoring 'error' events. Listeners installed using this symbol are called before the regular 'error' listeners are called.

Installing a listener using this symbol does not change the behavior once an 'error' event is emitted, therefore the process will still crash if no regular 'error' listener is installed.

Inherited from

TransportStream.errorMonitor

Methods

_construct

Optional _construct(callback): void

Parameters

NameType
callback(error?: Error) => void

Returns

void

Inherited from

TransportStream._construct


_destroy

_destroy(error, callback): void

Parameters

NameType
errorError
callback(error?: Error) => void

Returns

void

Inherited from

TransportStream._destroy


_final

_final(callback): void

Parameters

NameType
callback(error?: Error) => void

Returns

void

Inherited from

TransportStream._final


_write

_write(chunk, encoding, callback): void

Parameters

NameType
chunkany
encodingBufferEncoding
callback(error?: Error) => void

Returns

void

Inherited from

TransportStream._write


_writev

Optional _writev(chunks, callback): void

Parameters

NameType
chunks{ chunk: any ; encoding: BufferEncoding }[]
callback(error?: Error) => void

Returns

void

Inherited from

TransportStream._writev


addListener

addListener(event, listener): LogToEvTransport

Event emitter The defined events on documents including:

  1. close
  2. drain
  3. error
  4. finish
  5. pipe
  6. unpipe

Parameters

NameType
event"close"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.addListener

addListener(event, listener): LogToEvTransport

Parameters

NameType
event"drain"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.addListener

addListener(event, listener): LogToEvTransport

Parameters

NameType
event"error"
listener(err: Error) => void

Returns

LogToEvTransport

Inherited from

TransportStream.addListener

addListener(event, listener): LogToEvTransport

Parameters

NameType
event"finish"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.addListener

addListener(event, listener): LogToEvTransport

Parameters

NameType
event"pipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.addListener

addListener(event, listener): LogToEvTransport

Parameters

NameType
event"unpipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.addListener

addListener(event, listener): LogToEvTransport

Parameters

NameType
eventstring | symbol
listener(...args: any[]) => void

Returns

LogToEvTransport

Inherited from

TransportStream.addListener


close

Optional close(): void

Returns

void

Inherited from

TransportStream.close


cork

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 implementingwritable._writev() may have an adverse effect on throughput.

See also: writable.uncork(), writable._writev().

Since

v0.11.2

Returns

void

Inherited from

TransportStream.cork


destroy

destroy(error?): LogToEvTransport

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 towrite() 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().

Since

v8.0.0

Parameters

NameTypeDescription
error?ErrorOptional, an error to emit with 'error' event.

Returns

LogToEvTransport

Inherited from

TransportStream.destroy


emit

emit(event): boolean

Parameters

NameType
event"close"

Returns

boolean

Inherited from

TransportStream.emit

emit(event): boolean

Parameters

NameType
event"drain"

Returns

boolean

Inherited from

TransportStream.emit

emit(event, err): boolean

Parameters

NameType
event"error"
errError

Returns

boolean

Inherited from

TransportStream.emit

emit(event): boolean

Parameters

NameType
event"finish"

Returns

boolean

Inherited from

TransportStream.emit

emit(event, src): boolean

Parameters

NameType
event"pipe"
srcReadable

Returns

boolean

Inherited from

TransportStream.emit

emit(event, src): boolean

Parameters

NameType
event"unpipe"
srcReadable

Returns

boolean

Inherited from

TransportStream.emit

emit(event, ...args): boolean

Parameters

NameType
eventstring | symbol
...argsany[]

Returns

boolean

Inherited from

TransportStream.emit


end

end(cb?): LogToEvTransport

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!'.
const fs = require('fs');
const file = fs.createWriteStream('example.txt');
file.write('hello, ');
file.end('world!');
// Writing more now is not allowed!

Since

v0.9.4

Parameters

NameType
cb?() => void

Returns

LogToEvTransport

Inherited from

TransportStream.end

end(chunk, cb?): LogToEvTransport

Parameters

NameType
chunkany
cb?() => void

Returns

LogToEvTransport

Inherited from

TransportStream.end

end(chunk, encoding, cb?): LogToEvTransport

Parameters

NameType
chunkany
encodingBufferEncoding
cb?() => void

Returns

LogToEvTransport

Inherited from

TransportStream.end


eventNames

eventNames(): (string | symbol)[]

Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or Symbols.

const EventEmitter = require('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) ]

Since

v6.0.0

Returns

(string | symbol)[]

Inherited from

TransportStream.eventNames


getMaxListeners

getMaxListeners(): number

Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to defaultMaxListeners.

Since

v1.0.0

Returns

number

Inherited from

TransportStream.getMaxListeners


listenerCount

listenerCount(eventName): number

Returns the number of listeners listening to the event named eventName.

Since

v3.2.0

Parameters

NameTypeDescription
eventNamestring | symbolThe name of the event being listened for

Returns

number

Inherited from

TransportStream.listenerCount


listeners

listeners(eventName): Function[]

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] ]

Since

v0.1.26

Parameters

NameType
eventNamestring | symbol

Returns

Function[]

Inherited from

TransportStream.listeners


log

log(info, callback): any

Parameters

NameType
infoany
callbackany

Returns

any

Overrides

TransportStream.log


logv

Optional logv(info, next): any

Parameters

NameType
infoany
next() => void

Returns

any

Inherited from

TransportStream.logv


off

off(eventName, listener): LogToEvTransport

Alias for emitter.removeListener().

Since

v10.0.0

Parameters

NameType
eventNamestring | symbol
listener(...args: any[]) => void

Returns

LogToEvTransport

Inherited from

TransportStream.off


on

on(event, listener): LogToEvTransport

Parameters

NameType
event"close"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.on

on(event, listener): LogToEvTransport

Parameters

NameType
event"drain"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.on

on(event, listener): LogToEvTransport

Parameters

NameType
event"error"
listener(err: Error) => void

Returns

LogToEvTransport

Inherited from

TransportStream.on

on(event, listener): LogToEvTransport

Parameters

NameType
event"finish"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.on

on(event, listener): LogToEvTransport

Parameters

NameType
event"pipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.on

on(event, listener): LogToEvTransport

Parameters

NameType
event"unpipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.on

on(event, listener): LogToEvTransport

Parameters

NameType
eventstring | symbol
listener(...args: any[]) => void

Returns

LogToEvTransport

Inherited from

TransportStream.on


once

once(event, listener): LogToEvTransport

Parameters

NameType
event"close"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.once

once(event, listener): LogToEvTransport

Parameters

NameType
event"drain"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.once

once(event, listener): LogToEvTransport

Parameters

NameType
event"error"
listener(err: Error) => void

Returns

LogToEvTransport

Inherited from

TransportStream.once

once(event, listener): LogToEvTransport

Parameters

NameType
event"finish"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.once

once(event, listener): LogToEvTransport

Parameters

NameType
event"pipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.once

once(event, listener): LogToEvTransport

Parameters

NameType
event"unpipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.once

once(event, listener): LogToEvTransport

Parameters

NameType
eventstring | symbol
listener(...args: any[]) => void

Returns

LogToEvTransport

Inherited from

TransportStream.once


pipe

pipe<T>(destination, options?): T

Type parameters

NameType
Textends WritableStream<T>

Parameters

NameType
destinationT
options?Object
options.end?boolean

Returns

T

Inherited from

TransportStream.pipe


prependListener

prependListener(event, listener): LogToEvTransport

Parameters

NameType
event"close"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependListener

prependListener(event, listener): LogToEvTransport

Parameters

NameType
event"drain"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependListener

prependListener(event, listener): LogToEvTransport

Parameters

NameType
event"error"
listener(err: Error) => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependListener

prependListener(event, listener): LogToEvTransport

Parameters

NameType
event"finish"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependListener

prependListener(event, listener): LogToEvTransport

Parameters

NameType
event"pipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependListener

prependListener(event, listener): LogToEvTransport

Parameters

NameType
event"unpipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependListener

prependListener(event, listener): LogToEvTransport

Parameters

NameType
eventstring | symbol
listener(...args: any[]) => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependListener


prependOnceListener

prependOnceListener(event, listener): LogToEvTransport

Parameters

NameType
event"close"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependOnceListener

prependOnceListener(event, listener): LogToEvTransport

Parameters

NameType
event"drain"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependOnceListener

prependOnceListener(event, listener): LogToEvTransport

Parameters

NameType
event"error"
listener(err: Error) => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependOnceListener

prependOnceListener(event, listener): LogToEvTransport

Parameters

NameType
event"finish"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependOnceListener

prependOnceListener(event, listener): LogToEvTransport

Parameters

NameType
event"pipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependOnceListener

prependOnceListener(event, listener): LogToEvTransport

Parameters

NameType
event"unpipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependOnceListener

prependOnceListener(event, listener): LogToEvTransport

Parameters

NameType
eventstring | symbol
listener(...args: any[]) => void

Returns

LogToEvTransport

Inherited from

TransportStream.prependOnceListener


rawListeners

rawListeners(eventName): Function[]

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

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');

Since

v9.4.0

Parameters

NameType
eventNamestring | symbol

Returns

Function[]

Inherited from

TransportStream.rawListeners


removeAllListeners

removeAllListeners(event?): LogToEvTransport

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.

Since

v0.1.26

Parameters

NameType
event?string | symbol

Returns

LogToEvTransport

Inherited from

TransportStream.removeAllListeners


removeListener

removeListener(event, listener): LogToEvTransport

Parameters

NameType
event"close"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.removeListener

removeListener(event, listener): LogToEvTransport

Parameters

NameType
event"drain"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.removeListener

removeListener(event, listener): LogToEvTransport

Parameters

NameType
event"error"
listener(err: Error) => void

Returns

LogToEvTransport

Inherited from

TransportStream.removeListener

removeListener(event, listener): LogToEvTransport

Parameters

NameType
event"finish"
listener() => void

Returns

LogToEvTransport

Inherited from

TransportStream.removeListener

removeListener(event, listener): LogToEvTransport

Parameters

NameType
event"pipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.removeListener

removeListener(event, listener): LogToEvTransport

Parameters

NameType
event"unpipe"
listener(src: Readable) => void

Returns

LogToEvTransport

Inherited from

TransportStream.removeListener

removeListener(event, listener): LogToEvTransport

Parameters

NameType
eventstring | symbol
listener(...args: any[]) => void

Returns

LogToEvTransport

Inherited from

TransportStream.removeListener


setDefaultEncoding

setDefaultEncoding(encoding): LogToEvTransport

The writable.setDefaultEncoding() method sets the default encoding for a Writable stream.

Since

v0.11.15

Parameters

NameTypeDescription
encodingBufferEncodingThe new default encoding

Returns

LogToEvTransport

Inherited from

TransportStream.setDefaultEncoding


setMaxListeners

setMaxListeners(n): LogToEvTransport

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 toInfinity (or 0) to indicate an unlimited number of listeners.

Returns a reference to the EventEmitter, so that calls can be chained.

Since

v0.3.5

Parameters

NameType
nnumber

Returns

LogToEvTransport

Inherited from

TransportStream.setMaxListeners


uncork

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() usingprocess.nextTick(). Doing so allows batching of allwritable.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().

Since

v0.11.2

Returns

void

Inherited from

TransportStream.uncork


write

write(chunk, callback?): 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 thehighWaterMark 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.

Since

v0.9.4

Parameters

NameTypeDescription
chunkanyOptional data to write. For streams not operating in object mode, chunk must be a string, Buffer or Uint8Array. For object mode streams, chunk may be any JavaScript value other than null.
callback?(error: Error) => voidCallback for when this chunk of data is flushed.

Returns

boolean

false 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.

Inherited from

TransportStream.write

write(chunk, encoding, callback?): boolean

Parameters

NameType
chunkany
encodingBufferEncoding
callback?(error: Error) => void

Returns

boolean

Inherited from

TransportStream.write


fromWeb

Static fromWeb(writableStream, options?): Writable

A utility method for creating a Writable from a web WritableStream.

Since

v17.0.0

Parameters

NameType
writableStreamWritableStream<any>
options?Pick<WritableOptions, "signal" | "decodeStrings" | "highWaterMark" | "objectMode">

Returns

Writable

Inherited from

TransportStream.fromWeb


getEventListeners

Static getEventListeners(emitter, name): Function[]

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

For EventEmitters this behaves exactly the same as calling .listeners on the emitter.

For EventTargets this is the only way to get the event listeners for the event target. This is useful for debugging and diagnostic purposes.

const { getEventListeners, EventEmitter } = require('events');

{
const ee = new EventEmitter();
const listener = () => console.log('Events are fun');
ee.on('foo', listener);
getEventListeners(ee, 'foo'); // [listener]
}
{
const et = new EventTarget();
const listener = () => console.log('Events are fun');
et.addEventListener('foo', listener);
getEventListeners(et, 'foo'); // [listener]
}

Since

v15.2.0, v14.17.0

Parameters

NameType
emitterEventEmitter | DOMEventTarget
namestring | symbol

Returns

Function[]

Inherited from

TransportStream.getEventListeners


listenerCount

Static listenerCount(emitter, eventName): number

A class method that returns the number of listeners for the given eventNameregistered on the given emitter.

const { EventEmitter, listenerCount } = require('events');
const myEmitter = new EventEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(listenerCount(myEmitter, 'event'));
// Prints: 2

Since

v0.9.12

Deprecated

Since v3.2.0 - Use listenerCount instead.

Parameters

NameTypeDescription
emitterEventEmitterThe emitter to query
eventNamestring | symbolThe event name

Returns

number

Inherited from

TransportStream.listenerCount


on

Static on(emitter, eventName, options?): AsyncIterableIterator<any>

const { on, EventEmitter } = require('events');

(async () => {
const ee = new EventEmitter();

// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});

for await (const event of on(ee, 'foo')) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();

Returns an AsyncIterator that iterates eventName events. It will throw if the EventEmitter emits 'error'. It removes all listeners when exiting the loop. The value returned by each iteration is an array composed of the emitted event arguments.

An AbortSignal can be used to cancel waiting on events:

const { on, EventEmitter } = require('events');
const ac = new AbortController();

(async () => {
const ee = new EventEmitter();

// Emit later on
process.nextTick(() => {
ee.emit('foo', 'bar');
ee.emit('foo', 42);
});

for await (const event of on(ee, 'foo', { signal: ac.signal })) {
// The execution of this inner block is synchronous and it
// processes one event at a time (even with await). Do not use
// if concurrent execution is required.
console.log(event); // prints ['bar'] [42]
}
// Unreachable here
})();

process.nextTick(() => ac.abort());

Since

v13.6.0, v12.16.0

Parameters

NameTypeDescription
emitterEventEmitter-
eventNamestringThe name of the event being listened for
options?StaticEventEmitterOptions-

Returns

AsyncIterableIterator<any>

that iterates eventName events emitted by the emitter

Inherited from

TransportStream.on


once

Static once(emitter, eventName, options?): Promise<any[]>

Creates a Promise that is fulfilled when the EventEmitter emits the given event or that is rejected if the EventEmitter emits 'error' while waiting. The Promise will resolve with an array of all the arguments emitted to the given event.

This method is intentionally generic and works with the web platform EventTarget interface, which has no special'error' event semantics and does not listen to the 'error' event.

const { once, EventEmitter } = require('events');

async function run() {
const ee = new EventEmitter();

process.nextTick(() => {
ee.emit('myevent', 42);
});

const [value] = await once(ee, 'myevent');
console.log(value);

const err = new Error('kaboom');
process.nextTick(() => {
ee.emit('error', err);
});

try {
await once(ee, 'myevent');
} catch (err) {
console.log('error happened', err);
}
}

run();

The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the 'error' event itself, then it is treated as any other kind of event without special handling:

const { EventEmitter, once } = require('events');

const ee = new EventEmitter();

once(ee, 'error')
.then(([err]) => console.log('ok', err.message))
.catch((err) => console.log('error', err.message));

ee.emit('error', new Error('boom'));

// Prints: ok boom

An AbortSignal can be used to cancel waiting for the event:

const { EventEmitter, once } = require('events');

const ee = new EventEmitter();
const ac = new AbortController();

async function foo(emitter, event, signal) {
try {
await once(emitter, event, { signal });
console.log('event emitted!');
} catch (error) {
if (error.name === 'AbortError') {
console.error('Waiting for the event was canceled!');
} else {
console.error('There was an error', error.message);
}
}
}

foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!

Since

v11.13.0, v10.16.0

Parameters

NameType
emitterNodeEventTarget
eventNamestring | symbol
options?StaticEventEmitterOptions

Returns

Promise<any[]>

Inherited from

TransportStream.once

Static once(emitter, eventName, options?): Promise<any[]>

Parameters

NameType
emitterDOMEventTarget
eventNamestring
options?StaticEventEmitterOptions

Returns

Promise<any[]>

Inherited from

TransportStream.once


setMaxListeners

Static setMaxListeners(n?, ...eventTargets): void

const {
setMaxListeners,
EventEmitter
} = require('events');

const target = new EventTarget();
const emitter = new EventEmitter();

setMaxListeners(5, target, emitter);

Since

v15.4.0

Parameters

NameTypeDescription
n?numberA non-negative number. The maximum number of listeners per EventTarget event.
...eventTargets(EventEmitter | DOMEventTarget)[]-

Returns

void

Inherited from

TransportStream.setMaxListeners


toWeb

Static toWeb(streamWritable): WritableStream<any>

A utility method for creating a web WritableStream from a Writable.

Since

v17.0.0

Parameters

NameType
streamWritableWritable

Returns

WritableStream<any>

Inherited from

TransportStream.toWeb