tessl/npm-p-event

Promisify an event by waiting for it to be emitted with support for async iteration and advanced event handling

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p-event

Name: tessl/npm-p-event
Author: tessl

p-event is a JavaScript library that promisifies event-based APIs by waiting for events to be emitted. It converts Node.js EventEmitter and DOM event patterns into Promise-based APIs for use with async/await, supporting advanced features like timeout handling, event filtering, cancellation, and async iteration.

Package Information

Package Name: p-event
Package Type: npm
Language: JavaScript (with TypeScript definitions)
Installation: npm install p-event

Core Imports

ES Modules:

import { pEvent, pEventMultiple, pEventIterator, TimeoutError } from 'p-event';

// Import specific types (TypeScript only)
import type { 
  Emitter, 
  CancelablePromise, 
  Options, 
  MultiArgumentsOptions,
  FilterFunction 
} from 'p-event';

CommonJS:

const { pEvent, pEventMultiple, pEventIterator, TimeoutError } = require('p-event');

Basic Usage

import { pEvent } from 'p-event';
import { EventEmitter } from 'node:events';

// Basic event promisification
const emitter = new EventEmitter();

try {
  // Wait for a single event
  const result = await pEvent(emitter, 'finish');
  console.log('Event emitted with:', result);
} catch (error) {
  // Handle error events or timeouts
  console.error('Event error:', error);
}

// DOM events in browser
await pEvent(document, 'DOMContentLoaded');
console.log('DOM ready');

Architecture

p-event is built around three core functions that provide different event handling patterns:

Single Event Promises: pEvent converts a single event emission into a Promise
Multiple Event Collection: pEventMultiple collects multiple event emissions into an array
Async Iteration: pEventIterator provides async iterator for continuous event streams
Universal Compatibility: Automatic detection of listener methods (on/off, addEventListener/removeEventListener)
Cancellation Support: All returned promises include .cancel() method for cleanup

Capabilities

Single Event Promisification

Core functionality for converting a single event emission into a Promise with full cancellation support.

function pEvent<EventName extends string | symbol, EmittedType extends unknown[]>(
  emitter: Emitter<EventName, EmittedType>,
  event: string | symbol | ReadonlyArray<string | symbol>,
  options: MultiArgumentsOptions<EmittedType>
): CancelablePromise<EmittedType>;

function pEvent<EventName extends string | symbol, EmittedType>(
  emitter: Emitter<EventName, [EmittedType]>,
  event: string | symbol | ReadonlyArray<string | symbol>,
  filter: FilterFunction<EmittedType>
): CancelablePromise<EmittedType>;

function pEvent<EventName extends string | symbol, EmittedType>(
  emitter: Emitter<EventName, [EmittedType]>,
  event: string | symbol | ReadonlyArray<string | symbol>,
  options?: Options<EmittedType>
): CancelablePromise<EmittedType>;

Usage Examples:

import { pEvent } from 'p-event';
import fs from 'node:fs';

// Basic usage
const stream = fs.createReadStream('file.txt');
await pEvent(stream, 'open');
console.log('File opened');

// With filter function
const result = await pEvent(emitter, 'data', value => value > 100);

// With options
const result = await pEvent(emitter, 'finish', {
  timeout: 5000,
  rejectionEvents: ['error', 'close'],
  multiArgs: true
});

// Cancellation
const promise = pEvent(emitter, 'finish');
// Later...
promise.cancel(); // Removes listeners and prevents settlement

Multiple Event Collection

Collects multiple event emissions before resolving to an array of values.

function pEventMultiple<EventName extends string | symbol, EmittedType extends unknown[]>(
  emitter: Emitter<EventName, EmittedType>,
  event: string | symbol | ReadonlyArray<string | symbol>,
  options: MultipleMultiArgumentsOptions<EmittedType>
): CancelablePromise<EmittedType[]>;

function pEventMultiple<EventName extends string | symbol, EmittedType>(
  emitter: Emitter<EventName, [EmittedType]>,
  event: string | symbol | ReadonlyArray<string | symbol>,
  options: MultipleOptions<EmittedType>
): CancelablePromise<EmittedType[]>;

type MultipleOptions<EmittedType extends unknown | unknown[]> = {
  /** Number of times the event needs to be emitted before promise resolves */
  readonly count: number;
  /** Whether to resolve the promise immediately (returned array will be mutated) */
  readonly resolveImmediately?: boolean;
} & Options<EmittedType>;

type MultipleMultiArgumentsOptions<EmittedType extends unknown[]> = {
  readonly multiArgs: true;
} & MultipleOptions<EmittedType>;

Usage Examples:

import { pEventMultiple } from 'p-event';

// Collect 3 events
const results = await pEventMultiple(emitter, 'data', { count: 3 });
console.log(results); // [value1, value2, value3]

// Immediate resolution with mutable array
const promise = pEventMultiple(emitter, 'message', {
  count: Infinity,
  resolveImmediately: true
});
const results = await promise;
// results array is mutated as events are emitted

Async Event Iteration

Creates an async iterator for continuous event stream processing with automatic cleanup.

function pEventIterator<EventName extends string | symbol, EmittedType extends unknown[]>(
  emitter: Emitter<EventName, EmittedType>,
  event: string | symbol | ReadonlyArray<string | symbol>,
  options: IteratorMultiArgumentsOptions<EmittedType>
): AsyncIterableIterator<EmittedType>;

function pEventIterator<EventName extends string | symbol, EmittedType>(
  emitter: Emitter<EventName, [EmittedType]>,
  event: string | symbol | ReadonlyArray<string | symbol>,
  filter: FilterFunction<EmittedType>
): AsyncIterableIterator<EmittedType>;

function pEventIterator<EventName extends string | symbol, EmittedType>(
  emitter: Emitter<EventName, [EmittedType]>,
  event: string | symbol | ReadonlyArray<string | symbol>,
  options?: IteratorOptions<EmittedType>
): AsyncIterableIterator<EmittedType>;

type IteratorOptions<EmittedType extends unknown | unknown[]> = {
  /** Maximum number of events before iterator ends @default Infinity */
  readonly limit?: number;
  /** Events that will end the iterator @default [] */
  readonly resolutionEvents?: ReadonlyArray<string | symbol>;
} & Options<EmittedType>;

type IteratorMultiArgumentsOptions<EmittedType extends unknown[]> = {
  multiArgs: true;
} & IteratorOptions<EmittedType>;

Event Iteration

Base Types and Interfaces

type AddRemoveListener<EventName extends string | symbol, Arguments extends unknown[]> = (
  event: EventName,
  listener: (...arguments: Arguments) => void
) => void;

type Emitter<EventName extends string | symbol, EmittedType extends unknown[]> = {
  on?: AddRemoveListener<EventName, EmittedType>;
  addListener?: AddRemoveListener<EventName, EmittedType>;
  addEventListener?: AddRemoveListener<EventName, EmittedType>;
  off?: AddRemoveListener<EventName, EmittedType>;
  removeListener?: AddRemoveListener<EventName, EmittedType>;
  removeEventListener?: AddRemoveListener<EventName, EmittedType>;
};

type FilterFunction<ElementType extends unknown | unknown[]> = (
  value: ElementType
) => boolean;

type CancelablePromise<ResolveType> = {
  cancel(): void;
} & Promise<ResolveType>;

type Options<EmittedType extends unknown | unknown[]> = {
  /** Events that will reject the promise. @default ['error'] */
  readonly rejectionEvents?: ReadonlyArray<string | symbol>;
  /** Return array of all arguments from callback instead of just first argument. @default false */
  readonly multiArgs?: boolean;
  /** Time in milliseconds before timing out. @default Infinity */
  readonly timeout?: number;
  /** Filter function for accepting an event */
  readonly filter?: FilterFunction<EmittedType>;
  /** AbortSignal to abort waiting for the event */
  readonly signal?: AbortSignal;
};

type MultiArgumentsOptions<EmittedType extends unknown[]> = {
  readonly multiArgs: true;
} & Options<EmittedType>;

Error Handling

TimeoutError is exported from the p-timeout dependency:

export {TimeoutError} from 'p-timeout';

Usage:

import { pEvent, TimeoutError } from 'p-event';

try {
  await pEvent(emitter, 'finish', { timeout: 1000 });
} catch (error) {
  if (error instanceof TimeoutError) {
    console.log('Promise timed out');
  } else {
    console.log('Other error:', error);
  }
}

Install with Tessl CLI

npx tessl i tessl/npm-p-event

Workspace: tessl
Visibility: Public
Created: 6 months ago
Last updated: about 1 month ago
Describes: pkg:npm/p-event@6.0.x
Publish Source: CLI
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