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/**
* Much of the Node.js core API is built around an idiomatic asynchronous
* event-driven architecture in which certain kinds of objects (called "emitters")
* emit named events that cause `Function` objects ("listeners") to be called.
*
* For instance: a `net.Server` object emits an event each time a peer
* connects to it; a `fs.ReadStream` emits an event when the file is opened;
* a `stream` emits an event whenever data is available to be read.
*
* All objects that emit events are instances of the `EventEmitter` class. These
* objects expose an `eventEmitter.on()` function that allows one or more
* functions to be attached to named events emitted by the object. Typically,
* event names are camel-cased strings but any valid JavaScript property key
* can be used.
*
* When the `EventEmitter` object emits an event, all of the functions attached
* to that specific event are called _synchronously_. Any values returned by the
* called listeners are _ignored_ and discarded.
*
* The following example shows a simple `EventEmitter` instance with a single
* listener. The `eventEmitter.on()` method is used to register listeners, while
* the `eventEmitter.emit()` method is used to trigger the event.
*
* ```js
* const EventEmitter = require('events');
*
* class MyEmitter extends EventEmitter {}
*
* const myEmitter = new MyEmitter();
* myEmitter.on('event', () => {
* console.log('an event occurred!');
* });
* myEmitter.emit('event');
* ```
* @see [source](https://github.com/nodejs/node/blob/v16.9.0/lib/events.js)
*/
declare module 'events' {
interface EventEmitterOptions {
/**
* Enables automatic capturing of promise rejection.
*/
captureRejections?: boolean | undefined;
}
interface NodeEventTarget {
once(eventName: string | symbol, listener: (...args: any[]) => void): this;
}
interface DOMEventTarget {
addEventListener(
eventName: string,
listener: (...args: any[]) => void,
opts?: {
once: boolean;
}
): any;
}
interface StaticEventEmitterOptions {
signal?: AbortSignal | undefined;
}
interface EventEmitter extends NodeJS.EventEmitter {}
/**
* The `EventEmitter` class is defined and exposed by the `events` module:
*
* ```js
* const EventEmitter = require('events');
* ```
*
* All `EventEmitter`s emit the event `'newListener'` when new listeners are
* added and `'removeListener'` when existing listeners are removed.
*
* It supports the following option:
* @since v0.1.26
*/
class EventEmitter {
constructor(options?: EventEmitterOptions);
/**
* 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](https://dom.spec.whatwg.org/#interface-eventtarget) interface, which has no special`'error'` event
* semantics and does not listen to the `'error'` event.
*
* ```js
* 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:
*
* ```js
* 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:
*
* ```js
* 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
*/
static once(emitter: NodeEventTarget, eventName: string | symbol, options?: StaticEventEmitterOptions): Promise<any[]>;
static once(emitter: DOMEventTarget, eventName: string, options?: StaticEventEmitterOptions): Promise<any[]>;
/**
* ```js
* 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:
*
* ```js
* 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
* @param eventName The name of the event being listened for
* @return that iterates `eventName` events emitted by the `emitter`
*/
static on(emitter: NodeJS.EventEmitter, eventName: string, options?: StaticEventEmitterOptions): AsyncIterableIterator<any>;
/**
* A class method that returns the number of listeners for the given `eventName`registered on the given `emitter`.
*
* ```js
* 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.
* @param emitter The emitter to query
* @param eventName The event name
*/
static listenerCount(emitter: NodeJS.EventEmitter, eventName: string | symbol): number;
/**
* Returns a copy of the array of listeners for the event named `eventName`.
*
* For `EventEmitter`s this behaves exactly the same as calling `.listeners` on
* the emitter.
*
* For `EventTarget`s this is the only way to get the event listeners for the
* event target. This is useful for debugging and diagnostic purposes.
*
* ```js
* 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
*/
static getEventListeners(emitter: DOMEventTarget | NodeJS.EventEmitter, name: string | symbol): Function[];
/**
* ```js
* const {
* setMaxListeners,
* EventEmitter
* } = require('events');
*
* const target = new EventTarget();
* const emitter = new EventEmitter();
*
* setMaxListeners(5, target, emitter);
* ```
* @since v15.4.0
* @param n A non-negative number. The maximum number of listeners per `EventTarget` event.
* @param eventsTargets 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.
*/
static setMaxListeners(n?: number, ...eventTargets: Array<DOMEventTarget | NodeJS.EventEmitter>): void;
/**
* 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.
*/
static readonly errorMonitor: unique symbol;
static readonly captureRejectionSymbol: unique symbol;
/**
* Sets or gets the default captureRejection value for all emitters.
*/
// TODO: These should be described using static getter/setter pairs:
static captureRejections: boolean;
static defaultMaxListeners: number;
}
import internal = require('node:events');
namespace EventEmitter {
// Should just be `export { EventEmitter }`, but that doesn't work in TypeScript 3.4
export { internal as EventEmitter };
export interface Abortable {
/**
* When provided the corresponding `AbortController` can be used to cancel an asynchronous action.
*/
signal?: AbortSignal | undefined;
}
}
global {
namespace NodeJS {
interface EventEmitter {
/**
* Alias for `emitter.on(eventName, listener)`.
* @since v0.1.26
*/
addListener(eventName: string | symbol, listener: (...args: any[]) => void): this;
/**
* Adds the `listener` function to the end of the listeners array for the
* event named `eventName`. No checks are made to see if the `listener` has
* already been added. Multiple calls passing the same combination of `eventName`and `listener` will result in the `listener` being added, and called, multiple
* times.
*
* ```js
* 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.
*
* ```js
* const myEE = new EventEmitter();
* myEE.on('foo', () => console.log('a'));
* myEE.prependListener('foo', () => console.log('b'));
* myEE.emit('foo');
* // Prints:
* // b
* // a
* ```
* @since v0.1.101
* @param eventName The name of the event.
* @param listener The callback function
*/
on(eventName: string | symbol, listener: (...args: any[]) => void): this;
/**
* Adds a **one-time**`listener` function for the event named `eventName`. The
* next time `eventName` is triggered, this listener is removed and then invoked.
*
* ```js
* 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.
*
* ```js
* const myEE = new EventEmitter();
* myEE.once('foo', () => console.log('a'));
* myEE.prependOnceListener('foo', () => console.log('b'));
* myEE.emit('foo');
* // Prints:
* // b
* // a
* ```
* @since v0.3.0
* @param eventName The name of the event.
* @param listener The callback function
*/
once(eventName: string | symbol, listener: (...args: any[]) => void): this;
/**
* Removes the specified `listener` from the listener array for the event named`eventName`.
*
* ```js
* 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.
*
* ```js
* 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 indices 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
* 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.
* @since v0.1.26
*/
removeListener(eventName: string | symbol, listener: (...args: any[]) => void): this;
/**
* Alias for `emitter.removeListener()`.
* @since v10.0.0
*/
off(eventName: string | symbol, listener: (...args: any[]) => void): 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.
* @since v0.1.26
*/
removeAllListeners(event?: string | symbol): this;
/**
* By default `EventEmitter`s 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.
* @since v0.3.5
*/
setMaxListeners(n: number): this;
/**
* Returns the current max listener value for the `EventEmitter` which is either
* set by `emitter.setMaxListeners(n)` or defaults to {@link defaultMaxListeners}.
* @since v1.0.0
*/
getMaxListeners(): number;
/**
* Returns a copy of the array of listeners for the event named `eventName`.
*
* ```js
* server.on('connection', (stream) => {
* console.log('someone connected!');
* });
* console.log(util.inspect(server.listeners('connection')));
* // Prints: [ [Function] ]
* ```
* @since v0.1.26
*/
listeners(eventName: string | symbol): Function[];
/**
* Returns a copy of the array of listeners for the event named `eventName`,
* including any wrappers (such as those created by `.once()`).
*
* ```js
* 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
*/
rawListeners(eventName: string | symbol): Function[];
/**
* 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.
*
* ```js
* const EventEmitter = require('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
* ```
* @since v0.1.26
*/
emit(eventName: string | symbol, ...args: any[]): boolean;
/**
* Returns the number of listeners listening to the event named `eventName`.
* @since v3.2.0
* @param eventName The name of the event being listened for
*/
listenerCount(eventName: string | symbol): number;
/**
* 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.
*
* ```js
* server.prependListener('connection', (stream) => {
* console.log('someone connected!');
* });
* ```
*
* Returns a reference to the `EventEmitter`, so that calls can be chained.
* @since v6.0.0
* @param eventName The name of the event.
* @param listener The callback function
*/
prependListener(eventName: string | symbol, listener: (...args: any[]) => void): this;
/**
* Adds a **one-time**`listener` function for the event named `eventName` to the_beginning_ of the listeners array. The next time `eventName` is triggered, this
* listener is removed, and then invoked.
*
* ```js
* server.prependOnceListener('connection', (stream) => {
* console.log('Ah, we have our first user!');
* });
* ```
*
* Returns a reference to the `EventEmitter`, so that calls can be chained.
* @since v6.0.0
* @param eventName The name of the event.
* @param listener The callback function
*/
prependOnceListener(eventName: string | symbol, listener: (...args: any[]) => void): this;
/**
* Returns an array listing the events for which the emitter has registered
* listeners. The values in the array are strings or `Symbol`s.
*
* ```js
* 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
*/
eventNames(): Array<string | symbol>;
}
}
}
export = EventEmitter;
}
declare module 'node:events' {
import events = require('events');
export = events;
}