mitm-core / Proxy

Class: Proxy

Defined in: src/lib/Proxy.ts:73

The main proxy server implementation.

Hierarchy

View Summary

Extends

• TypedEventEmitter<ProxyEventMap>

Implements

• IProxy

Constructors

Constructor

new Proxy(options?): Proxy

Defined in: src/lib/Proxy.ts:345

Creates and configures a proxy instance.

Uses the provided HTTP server or creates a new one, applies the configured defaults, initializes plugin event handling, registers middleware pipelines, binds proxy events, and registers the global proxy configuration.

Parameters

options?

ProxyOptions = {}

Configuration options for the proxy instance.

Returns

Proxy

Remarks

• Certificate caching is enabled by default.
• Response caching is disabled by default.
• Default processing pipelines are enabled by default.
• Handshake timeout defaults to 10 seconds.
• Upstream timeout defaults to 30 seconds.
• Plugin execution timeout defaults to 10 seconds.
• If no root CA credentials are provided, empty key and certificate values are used.

Example

const proxy = new Proxy({
  useResponseCache: true,
  handshakeTimeoutMs: 15_000,
  upstreamTimeoutMs: 45_000,
});

Overrides

TypedEventEmitter<ProxyEventMap>.constructor

Properties

listeners

listeners: any

Defined in: src/lib/Proxy.ts:312

Returns the registered listeners for the specified event.

The returned callbacks are typed according to the event's argument tuple.

Type Param

K

The event key.

Param

event

The event whose listeners should be retrieved.

Returns

An array of listener callbacks.

Overrides

TypedEventEmitter.listeners

---

captureRejections

static captureRejections: boolean

Defined in: node_modules/@types/node/events.d.ts:416

Value: boolean

Change the default captureRejections option on all new EventEmitter objects.

Since

v13.4.0, v12.16.0

Inherited from

TypedEventEmitter.captureRejections

---

captureRejectionSymbol

readonly static captureRejectionSymbol: typeof captureRejectionSymbol

Defined in: node_modules/@types/node/events.d.ts:409

Value: Symbol.for('nodejs.rejection')

See how to write a custom rejection handler.

Since

v13.4.0, v12.16.0

Inherited from

TypedEventEmitter.captureRejectionSymbol

---

defaultMaxListeners

static defaultMaxListeners: number

Defined in: node_modules/@types/node/events.d.ts:455

By default, a maximum of 10 listeners can be registered for any single event. This limit can be changed for individual EventEmitter instances using the emitter.setMaxListeners(n) method. To change the default for allEventEmitter instances, the events.defaultMaxListeners property can be used. If this value is not a positive number, a RangeError is thrown.

Take caution when setting the events.defaultMaxListeners because the change affects all EventEmitter instances, including those created before the change is made. However, calling emitter.setMaxListeners(n) still has precedence over events.defaultMaxListeners.

This is not a hard limit. The EventEmitter instance will allow more listeners to be added but will output a trace warning to stderr indicating that a "possible EventEmitter memory leak" has been detected. For any single EventEmitter, the emitter.getMaxListeners() and emitter.setMaxListeners() methods can be used to temporarily avoid this warning:

import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', () => {
  // do stuff
  emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});

The --trace-warnings command-line flag can be used to display the stack trace for such warnings.

The emitted warning can be inspected with process.on('warning') and will have the additional emitter, type, and count properties, referring to the event emitter instance, the event's name and the number of attached listeners, respectively. Its name property is set to 'MaxListenersExceededWarning'.

Since

v0.11.2

Inherited from

TypedEventEmitter.defaultMaxListeners

---

errorMonitor

readonly static errorMonitor: typeof errorMonitor

Defined in: node_modules/@types/node/events.d.ts:402

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.

Since

v13.6.0, v12.17.0

Inherited from

TypedEventEmitter.errorMonitor

Methods

[captureRejectionSymbol]()?

optional [captureRejectionSymbol]<K>(error, event, ...args): void

Defined in: node_modules/@types/node/events.d.ts:103

Type Parameters

K

K

Parameters

error

Error

event

string | symbol

args

...AnyRest

Returns

void

Inherited from

TypedEventEmitter.[captureRejectionSymbol]

---

addListener()

addListener<K>(event, listener): this

Defined in: src/lib/Proxy.ts:287

Type Parameters

K

K extends keyof ProxyEventMap

Parameters

event

K

listener

ProxyEventMap[K] extends any[] ? (...args) => void | Promise<void> : never

Returns

this

Overrides

TypedEventEmitter.addListener

---

address()

address(): string | AddressInfo | null

Defined in: src/lib/Proxy.ts:589

Returns

string | AddressInfo | null

---

emit()

emit<K>(event, ...args): boolean

Defined in: src/core/event/EventBus.ts:85

Emits the specified event synchronously.

Registered listeners are invoked according to Node.js EventEmitter semantics. This method does not wait for promises returned by listeners.

Type Parameters

K

K extends "error" | "connection:open" | "connect:request" | "connect:before" | "connect:established" | "http:request" | "https:request" | "ws:request" | "ws:established" | "ws:client-message" | "ws:upstream-message" | "ws:close" | "ws:error"

The event key.

Parameters

event

K

The event to emit.

args

...ProxyEventMap[K] extends any[] ? any[any] : []

Arguments associated with the event.

Returns

boolean

true if the event had listeners, otherwise false.

Inherited from

TypedEventEmitter.emit

---

emitAsync()

emitAsync<K>(eventName, ...args): Promise<void>

Defined in: src/core/event/EventBus.ts:168

Executes all listeners for an event concurrently and asynchronously.

Each listener is invoked, and its return value is normalized to a promise. This method waits for all listener promises to settle before completing, even if one or more listeners reject.

If no listeners are registered, the method resolves immediately.

If a single listener rejects, its rejection reason is thrown directly. If multiple listeners reject, an aggregate error is thrown containing their error messages.

Type Parameters

K

K extends keyof ProxyEventMap

The event key.

Parameters

eventName

K

The event to emit.

args

...ProxyEventMap[K] extends any[] ? any[any] : never[]

Arguments associated with the event.

Returns

Promise<void>

A promise that resolves when all listeners succeed.

Throws

The rejection reason when one listener fails, or an aggregate error when multiple listeners fail.

Inherited from

TypedEventEmitter.emitAsync

---

eventNames()

eventNames(): (string | symbol)[]

Defined in: node_modules/@types/node/events.d.ts:958

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

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) ]

Returns

(string | symbol)[]

Since

v6.0.0

Inherited from

TypedEventEmitter.eventNames

---

getMaxListeners()

getMaxListeners(): number

Defined in: node_modules/@types/node/events.d.ts:810

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

Returns

number

Since

v1.0.0

Inherited from

TypedEventEmitter.getMaxListeners

---

listen()

listen(port, callback?): Promise<void>

Defined in: src/lib/Proxy.ts:510

Starts the proxy's HTTP server.

Parameters

port

number

Port to listen on. Use 0 to request an available port.

callback?

() => void | Promise<void>

Optional callback invoked after the server starts.

Returns

Promise<void>

A promise representing startup.

Implementation of

IProxy.listen

---

listenerCount()

listenerCount(eventName, listener?): number

Defined in: src/core/event/EventBus.ts:123

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.

Parameters

eventName

string | symbol

The name of the event being listened for

listener?

(...args) => void

The event handler function

Returns

number

Since

v3.2.0

Inherited from

TypedEventEmitter.listenerCount

---

off()

off<K>(event, listener): this

Defined in: src/lib/Proxy.ts:277

Removes a previously registered listener for the specified event.

The listener must match the callback registered with the emitter.

Type Parameters

K

K extends keyof ProxyEventMap

The event key.

Parameters

event

K

The event from which to remove the listener.

listener

ProxyEventMap[K] extends any[] ? (...args) => void | Promise<void> : never

The listener callback to remove.

Returns

this

This emitter instance for method chaining.

Overrides

TypedEventEmitter.off

---

on()

on<K>(event, listener): this

Defined in: src/lib/Proxy.ts:257

Registers a listener for the specified event.

The listener's parameters are inferred from the argument tuple associated with the event in the event map.

Type Parameters

K

K extends keyof ProxyEventMap

The event key.

Parameters

event

K

The event to listen for.

listener

ProxyEventMap[K] extends any[] ? (...args) => void | Promise<void> : never

The callback invoked when the event is emitted.

Returns

this

This emitter instance for method chaining.

Overrides

TypedEventEmitter.on

---

once()

once<K>(event, listener): this

Defined in: src/lib/Proxy.ts:267

Registers a listener that is invoked at most once for the specified event.

The listener's parameters are inferred from the event's argument tuple.

Type Parameters

K

K extends keyof ProxyEventMap

The event key.

Parameters

event

K

The event to listen for.

listener

ProxyEventMap[K] extends any[] ? (...args) => void | Promise<void> : never

The callback invoked the first time the event is emitted.

Returns

this

This emitter instance for method chaining.

Overrides

TypedEventEmitter.once

---

prependListener()

prependListener<K>(eventName, listener): this

Defined in: node_modules/@types/node/events.d.ts:922

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.

Type Parameters

K

K

Parameters

eventName

string | symbol

The name of the event.

listener

(...args) => void

The callback function

Returns

this

Since

v6.0.0

Inherited from

TypedEventEmitter.prependListener

---

prependOnceListener()

prependOnceListener<K>(eventName, listener): this

Defined in: node_modules/@types/node/events.d.ts:938

Adds a one-timelistener 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.

Type Parameters

K

K

Parameters

eventName

string | symbol

The name of the event.

listener

(...args) => void

The callback function

Returns

this

Since

v6.0.0

Inherited from

TypedEventEmitter.prependOnceListener

---

rawListeners()

rawListeners<K>(eventName): Function[]

Defined in: node_modules/@types/node/events.d.ts:854

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');

Type Parameters

K

K

Parameters

eventName

string | symbol

Returns

Function[]

Since

v9.4.0

Inherited from

TypedEventEmitter.rawListeners

---

removeAllListeners()

removeAllListeners(event?): this

Defined in: src/lib/Proxy.ts:305

Removes all listeners for the specified event, or all events when no event is provided.

Parameters

event?

"error" | "connection:open" | "connect:request" | "connect:before" | "connect:established" | "http:request" | "https:request" | "ws:request" | "ws:established" | "ws:client-message" | "ws:upstream-message" | "ws:close" | "ws:error"

The event whose listeners should be removed. If omitted, listeners for all events are removed.

Returns

this

This emitter instance for method chaining.

Overrides

TypedEventEmitter.removeAllListeners

---

removeListener()

removeListener<K>(event, listener): this

Defined in: src/lib/Proxy.ts:296

Type Parameters

K

K extends keyof ProxyEventMap

Parameters

event

K

listener

ProxyEventMap[K] extends any[] ? (...args) => void | Promise<void> : never

Returns

this

Overrides

TypedEventEmitter.removeListener

---

setMaxListeners()

setMaxListeners(n): this

Defined in: node_modules/@types/node/events.d.ts:804

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.

Parameters

n

number

Returns

this

Since

v0.3.5

Inherited from

TypedEventEmitter.setMaxListeners

---

stop()

stop(shutdownTimeoutMs?): Promise<void>

Defined in: src/lib/Proxy.ts:576

Gracefully shuts down the proxy, allowing active requests to drain until the shutdown timeout expires before forcing cleanup.

Parameters

shutdownTimeoutMs?

number = 1500

Maximum time to wait for active requests. Defaults to 1500 ms.

Returns

Promise<void>

A promise that resolves when shutdown completes.

Implementation of

IProxy.stop

---

unuse()

unuse(plugin): this

Defined in: src/lib/Proxy.ts:494

Unregisters a plugin before the proxy starts. Does nothing if the plugin is not registered.

Parameters

plugin

BasePlugin<any>

Plugin to unregister.

Returns

this

The current proxy instance for chaining.

Throws

If the proxy is starting, running, or has been stopped.

Implementation of

IProxy.unuse

---

use()

use<K>(plugin): this

Defined in: src/lib/Proxy.ts:473

Registers a plugin before the proxy starts. Duplicate registration of the same plugin instance is ignored.

Type Parameters

K

K extends keyof PluginEventMap

Parameters

plugin

BasePlugin<K>

Plugin to register.

Returns

this

The current proxy instance for chaining.

Throws

If the proxy is starting, running, or has been stopped.

Implementation of

IProxy.use

---

addAbortListener()

static addAbortListener(signal, resource): Disposable

Defined in: node_modules/@types/node/events.d.ts:394

Listens once to the abort event on the provided signal.

Listening to the abort event on abort signals is unsafe and may lead to resource leaks since another third party with the signal can call e.stopImmediatePropagation(). Unfortunately Node.js cannot change this since it would violate the web standard. Additionally, the original API makes it easy to forget to remove listeners.

This API allows safely using AbortSignals in Node.js APIs by solving these two issues by listening to the event such that stopImmediatePropagation does not prevent the listener from running.

Returns a disposable so that it may be unsubscribed from more easily.

import { addAbortListener } from 'node:events';

function example(signal) {
  signal.addEventListener('abort', (e) => e.stopImmediatePropagation());
  // addAbortListener() returns a disposable, so the `using` keyword ensures
  // the abort listener is automatically removed when this scope exits.
  using _ = addAbortListener(signal, (e) => {
    // Do something when signal is aborted.
  });
}

Parameters

signal

AbortSignal

resource

(event) => void

Returns

Disposable

Disposable that removes the abort listener.

Since

v20.5.0

Inherited from

TypedEventEmitter.addAbortListener

---

getEventListeners()

static getEventListeners(emitter, name): Function[]

Defined in: node_modules/@types/node/events.d.ts:319

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.

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

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

Parameters

emitter

EventEmitter<DefaultEventMap> | EventTarget

name

string | symbol

Returns

Function[]

Since

v15.2.0, v14.17.0

Inherited from

TypedEventEmitter.getEventListeners

---

getMaxListeners()

static getMaxListeners(emitter): number

Defined in: node_modules/@types/node/events.d.ts:348

Returns the currently set max amount of listeners.

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

For EventTargets this is the only way to get the max event listeners for the event target. If the number of event handlers on a single EventTarget exceeds the max set, the EventTarget will print a warning.

import { getMaxListeners, setMaxListeners, EventEmitter } from 'node:events';

{
  const ee = new EventEmitter();
  console.log(getMaxListeners(ee)); // 10
  setMaxListeners(11, ee);
  console.log(getMaxListeners(ee)); // 11
}
{
  const et = new EventTarget();
  console.log(getMaxListeners(et)); // 10
  setMaxListeners(11, et);
  console.log(getMaxListeners(et)); // 11
}

Parameters

emitter

EventEmitter<DefaultEventMap> | EventTarget

Returns

number

Since

v19.9.0

Inherited from

TypedEventEmitter.getMaxListeners

---

listenerCount()

Call Signature

static listenerCount(emitter, eventName): number

Defined in: node_modules/@types/node/events.d.ts:290

Returns the number of registered listeners for the event named eventName.

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

For EventTargets this is the only way to obtain the listener count. This can be useful for debugging and diagnostic purposes.

Parameters

emitter

EventEmitter

eventName

string | symbol

Returns

number

Since

v0.9.12

Inherited from

TypedEventEmitter.listenerCount

Call Signature

static listenerCount(emitter, eventName): number

Defined in: node_modules/@types/node/events.d.ts:291

Returns the number of registered listeners for the event named eventName.

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

For EventTargets this is the only way to obtain the listener count. This can be useful for debugging and diagnostic purposes.

Parameters

emitter

EventTarget

eventName

string

Returns

number

Since

v0.9.12

Inherited from

TypedEventEmitter.listenerCount

---

on()

Call Signature

static on(emitter, eventName, options?): AsyncIterator<any[]>

Defined in: node_modules/@types/node/events.d.ts:270

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

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:

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

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());

Use the close option to specify an array of event names that will end the iteration:

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

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

for await (const event of on(ee, 'foo', { close: ['close'] })) {
  console.log(event); // prints ['bar'] [42]
}
// the loop will exit after 'close' is emitted
console.log('done'); // prints 'done'

Parameters

emitter

EventEmitter

eventName

string | symbol

options?

StaticEventEmitterIteratorOptions

Returns

AsyncIterator<any[]>

An AsyncIterator that iterates eventName events emitted by the emitter

Since

v13.6.0, v12.16.0

Inherited from

TypedEventEmitter.on

Call Signature

static on(emitter, eventName, options?): AsyncIterator<any[]>

Defined in: node_modules/@types/node/events.d.ts:275

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

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:

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

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());

Use the close option to specify an array of event names that will end the iteration:

import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

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

for await (const event of on(ee, 'foo', { close: ['close'] })) {
  console.log(event); // prints ['bar'] [42]
}
// the loop will exit after 'close' is emitted
console.log('done'); // prints 'done'

Parameters

emitter

EventTarget

eventName

string

options?

StaticEventEmitterIteratorOptions

Returns

AsyncIterator<any[]>

An AsyncIterator that iterates eventName events emitted by the emitter

Since

v13.6.0, v12.16.0

Inherited from

TypedEventEmitter.on

---

once()

Call Signature

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

Defined in: node_modules/@types/node/events.d.ts:184

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.

import { once, EventEmitter } from 'node:events';
import process from 'node:process';

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.error('error happened', err);
}

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:

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

const ee = new EventEmitter();

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

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

// Prints: ok boom

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

import { EventEmitter, once } from 'node: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!

Parameters

emitter

EventEmitter

eventName

string | symbol

options?

StaticEventEmitterOptions

Returns

Promise<any[]>

Since

v11.13.0, v10.16.0

Inherited from

TypedEventEmitter.once

Call Signature

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

Defined in: node_modules/@types/node/events.d.ts:189

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.

import { once, EventEmitter } from 'node:events';
import process from 'node:process';

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.error('error happened', err);
}

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:

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

const ee = new EventEmitter();

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

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

// Prints: ok boom

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

import { EventEmitter, once } from 'node: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!

Parameters

emitter

EventTarget

eventName

string

options?

StaticEventEmitterOptions

Returns

Promise<any[]>

Since

v11.13.0, v10.16.0

Inherited from

TypedEventEmitter.once

---

setMaxListeners()

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

Defined in: node_modules/@types/node/events.d.ts:363

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

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

setMaxListeners(5, target, emitter);

Parameters

n?

number

A non-negative number. The maximum number of listeners per EventTarget event.

eventTargets

...(EventEmitter<DefaultEventMap> | EventTarget)[]

Zero or more {EventTarget} or {EventEmitter} instances. If none are specified, n is set as the default max for all newly created {EventTarget} and {EventEmitter} objects.

Returns

void

Since

v15.4.0

Inherited from

TypedEventEmitter.setMaxListeners