events.d.ts

/**
 * 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/v18.0.0/lib/events.js)
 */
declare module 'events' {
    // NOTE: This class is in the docs but is **not actually exported** by Node.
    // If https://github.com/nodejs/node/issues/39903 gets resolved and Node
    // actually starts exporting the class, uncomment below.

    // import { EventListener, EventListenerObject } from '__dom-events';
    // /** The NodeEventTarget is a Node.js-specific extension to EventTarget that emulates a subset of the EventEmitter API. */
    // interface NodeEventTarget extends EventTarget {
    //     /**
    //      * Node.js-specific extension to the `EventTarget` class that emulates the equivalent `EventEmitter` API.
    //      * The only difference between `addListener()` and `addEventListener()` is that addListener() will return a reference to the EventTarget.
    //      */
    //     addListener(type: string, listener: EventListener | EventListenerObject, options?: { once: boolean }): this;
    //     /** Node.js-specific extension to the `EventTarget` class that returns an array of event `type` names for which event listeners are registered. */
    //     eventNames(): string[];
    //     /** Node.js-specific extension to the `EventTarget` class that returns the number of event listeners registered for the `type`. */
    //     listenerCount(type: string): number;
    //     /** Node.js-specific alias for `eventTarget.removeListener()`. */
    //     off(type: string, listener: EventListener | EventListenerObject): this;
    //     /** Node.js-specific alias for `eventTarget.addListener()`. */
    //     on(type: string, listener: EventListener | EventListenerObject, options?: { once: boolean }): this;
    //     /** Node.js-specific extension to the `EventTarget` class that adds a `once` listener for the given event `type`. This is equivalent to calling `on` with the `once` option set to `true`. */
    //     once(type: string, listener: EventListener | EventListenerObject): this;
    //     /**
    //      * Node.js-specific extension to the `EventTarget` class.
    //      * If `type` is specified, removes all registered listeners for `type`,
    //      * otherwise removes all registered listeners.
    //      */
    //     removeAllListeners(type: string): this;
    //     /**
    //      * Node.js-specific extension to the `EventTarget` class that removes the listener for the given `type`.
    //      * The only difference between `removeListener()` and `removeEventListener()` is that `removeListener()` will return a reference to the `EventTarget`.
    //      */
    //     removeListener(type: string, listener: EventListener | EventListenerObject): this;
    // }

    interface EventEmitterOptions {
        /**
         * Enables automatic capturing of promise rejection.
         */
        captureRejections?: boolean | undefined;
    }
    // Any EventTarget with a Node-style `once` function
    interface _NodeEventTarget {
        once(eventName: string | symbol, listener: (...args: any[]) => void): this;
    }
    // Any EventTarget with a DOM-style `addEventListener`
    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, v14.17.0
         */
        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;
}