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@ethereumjs/util / AsyncEventEmitter

Class: AsyncEventEmitter<T>

Type parameters

Name Type
T extends EventMap

Hierarchy

  • EventEmitter

    ↳ AsyncEventEmitter

Table of contents

Constructors

Properties

Methods

Constructors

constructor

• new AsyncEventEmitter<T>(options?)

Type parameters

Name Type
T extends EventMap

Parameters

Name Type
options? EventEmitterOptions

Inherited from

EventEmitter.constructor

Defined in

node_modules/@types/node/ts4.8/events.d.ts:111

Properties

captureRejectionSymbol

▪ Static Readonly captureRejectionSymbol: typeof captureRejectionSymbol

Inherited from

EventEmitter.captureRejectionSymbol

Defined in

node_modules/@types/node/ts4.8/events.d.ts:328

captureRejections

▪ Static captureRejections: boolean

Sets or gets the default captureRejection value for all emitters.

Inherited from

EventEmitter.captureRejections

Defined in

node_modules/@types/node/ts4.8/events.d.ts:333

defaultMaxListeners

▪ Static defaultMaxListeners: number

Inherited from

EventEmitter.defaultMaxListeners

Defined in

node_modules/@types/node/ts4.8/events.d.ts:334

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

EventEmitter.errorMonitor

Defined in

node_modules/@types/node/ts4.8/events.d.ts:327

Methods

addListener

▸ addListener<E>(event, listener): AsyncEventEmitter<T>

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
listener T[E]

Returns

AsyncEventEmitter<T>

Overrides

EventEmitter.addListener

Defined in

packages/util/src/asyncEventEmitter.ts:173

after

▸ after<E>(event, target, listener): AsyncEventEmitter<T>

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
target T[E]
listener T[E]

Returns

AsyncEventEmitter<T>

Defined in

packages/util/src/asyncEventEmitter.ts:127

before

▸ before<E>(event, target, listener): AsyncEventEmitter<T>

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
target T[E]
listener T[E]

Returns

AsyncEventEmitter<T>

Defined in

packages/util/src/asyncEventEmitter.ts:123

emit

▸ emit<E>(event, ...args): boolean

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
...args Parameters<T[E]>

Returns

boolean

Overrides

EventEmitter.emit

Defined in

packages/util/src/asyncEventEmitter.ts:50

eventNames

▸ eventNames(): keyof T & string[]

Returns

keyof T & string[]

Overrides

EventEmitter.eventNames

Defined in

packages/util/src/asyncEventEmitter.ts:193

first

▸ first<E>(event, listener): AsyncEventEmitter<T>

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
listener T[E]

Returns

AsyncEventEmitter<T>

Defined in

packages/util/src/asyncEventEmitter.ts:105

getMaxListeners

▸ getMaxListeners(): number

Returns

number

Overrides

EventEmitter.getMaxListeners

Defined in

packages/util/src/asyncEventEmitter.ts:205

listenerCount

▸ listenerCount(event): number

Parameters

Name Type
event keyof T & string

Returns

number

Overrides

EventEmitter.listenerCount

Defined in

packages/util/src/asyncEventEmitter.ts:201

listeners

▸ listeners<E>(event): T[E][]

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string

Returns

T[E][]

Overrides

EventEmitter.listeners

Defined in

packages/util/src/asyncEventEmitter.ts:197

off

▸ off(eventName, listener): AsyncEventEmitter<T>

Alias for emitter.removeListener().

Since

v10.0.0

Parameters

Name Type
eventName string | symbol
listener (...args: any[]) => void

Returns

AsyncEventEmitter<T>

Inherited from

EventEmitter.off

Defined in

node_modules/@types/node/ts4.8/events.d.ts:499

on

▸ on<E>(event, listener): AsyncEventEmitter<T>

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
listener T[E]

Returns

AsyncEventEmitter<T>

Overrides

EventEmitter.on

Defined in

packages/util/src/asyncEventEmitter.ts:169

once

▸ once<E>(event, listener): AsyncEventEmitter<T>

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
listener T[E]

Returns

AsyncEventEmitter<T>

Overrides

EventEmitter.once

Defined in

packages/util/src/asyncEventEmitter.ts:79

prependListener

▸ prependListener<E>(event, listener): AsyncEventEmitter<T>

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
listener T[E]

Returns

AsyncEventEmitter<T>

Overrides

EventEmitter.prependListener

Defined in

packages/util/src/asyncEventEmitter.ts:177

prependOnceListener

▸ prependOnceListener<E>(event, listener): AsyncEventEmitter<T>

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
listener T[E]

Returns

AsyncEventEmitter<T>

Overrides

EventEmitter.prependOnceListener

Defined in

packages/util/src/asyncEventEmitter.ts:181

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

Name Type
eventName string | symbol

Returns

Function[]

Inherited from

EventEmitter.rawListeners

Defined in

node_modules/@types/node/ts4.8/events.d.ts:569

removeAllListeners

▸ removeAllListeners(event?): AsyncEventEmitter<T>

Parameters

Name Type
event? keyof T & string

Returns

AsyncEventEmitter<T>

Overrides

EventEmitter.removeAllListeners

Defined in

packages/util/src/asyncEventEmitter.ts:185

removeListener

▸ removeListener<E>(event, listener): AsyncEventEmitter<T>

Type parameters

Name Type
E extends string | number | symbol

Parameters

Name Type
event E & string
listener T[E]

Returns

AsyncEventEmitter<T>

Overrides

EventEmitter.removeListener

Defined in

packages/util/src/asyncEventEmitter.ts:189

setMaxListeners

▸ setMaxListeners(maxListeners): AsyncEventEmitter<T>

Parameters

Name Type
maxListeners number

Returns

AsyncEventEmitter<T>

Overrides

EventEmitter.setMaxListeners

Defined in

packages/util/src/asyncEventEmitter.ts:209

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

Name Type
emitter EventEmitter | _DOMEventTarget
name string | symbol

Returns

Function[]

Inherited from

EventEmitter.getEventListeners

Defined in

node_modules/@types/node/ts4.8/events.d.ts:299

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

Name Type Description
emitter EventEmitter The emitter to query
eventName string | symbol The event name

Returns

number

Inherited from

EventEmitter.listenerCount

Defined in

node_modules/@types/node/ts4.8/events.d.ts:271

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

Name Type Description
emitter EventEmitter -
eventName string The name of the event being listened for
options? StaticEventEmitterOptions -

Returns

AsyncIterableIterator<any>

that iterates eventName events emitted by the emitter

Inherited from

EventEmitter.on

Defined in

node_modules/@types/node/ts4.8/events.d.ts:254

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

Name Type
emitter _NodeEventTarget
eventName string | symbol
options? StaticEventEmitterOptions

Returns

Promise<any[]>

Inherited from

EventEmitter.once

Defined in

node_modules/@types/node/ts4.8/events.d.ts:194

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

Parameters

Name Type
emitter _DOMEventTarget
eventName string
options? StaticEventEmitterOptions

Returns

Promise<any[]>

Inherited from

EventEmitter.once

Defined in

node_modules/@types/node/ts4.8/events.d.ts:195

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

Name Type Description
n? number A non-negative number. The maximum number of listeners per EventTarget event.
...eventTargets (EventEmitter | _DOMEventTarget)[] -

Returns

void

Inherited from

EventEmitter.setMaxListeners

Defined in

node_modules/@types/node/ts4.8/events.d.ts:317