p-event

Promisify an event by waiting for it to be emitted

Useful when you need only one event emission and want to use it with promises or await it in an async function.

Install

$ npm install --save p-event

Usage

const pEvent = require('p-event');
const emitter = require('./some-event-emitter');

pEvent(emitter, 'finish')
	// Called when `emitter` emits a `finish` event
	.then(result => {
		console.log(result);
	})
	// Called when `emitter` emits an `error` event
	.catch(error => {
		console.error(error);
	});

const pEvent = require('p-event');

pEvent(document, 'DOMContentLoaded').then(() => {
	console.log('😎');
});

API

pEvent(emitter, event, [options])

Returns a Promise that is fulfilled when emitter emits an event matching event, or rejects if emitter emits any of the events defined in the rejectionEvents option.

The returned promise has a .cancel() method, which when called, removes the event listeners and causes the promise to never be settled.

emitter

Type: Object

Event emitter object.

Should have either a .on()/.addListener()/.addEventListener() and .off()/.removeListener()/.removeEventListener() method, like the Node.js EventEmitter and DOM events.

event

Type: string

Name of the event to listen to.

If the same event is defined both here and in rejectionEvents, this one takes priority.

options

Type: Object

rejectionEvents

Type: Array
Default: ['error']

Events that will reject the promise.

Before and after

const fs = require('fs');

function getOpenReadStream(file, callback) {
	const stream = fs.createReadStream(file);

	stream.on('open', () => {
		callback(null, stream);
	});

	stream.on('error', error => {
		callback(error);
	});
}

getOpenReadStream('unicorn.txt', (error, stream) => {
	if (error) {
		console.error(error);
		return;
	}

	console.log('File descriptor:', stream.fd);
	stream.pipe(process.stdout);
});

const fs = require('fs');
const pEvent = require('p-event');

async function getOpenReadStream(file) {
	const stream = fs.createReadStream(file);
	await pEvent(stream, 'open');
	return stream;
}

getOpenReadStream('unicorn.txt')
	.then(stream => {
		console.log('File descriptor:', stream.fd);
		stream.pipe(process.stdout);
	})
	.catch(console.error);

Related

• pify - Promisify a callback-style function
• p-map - Map over promises concurrently
• More…

License

MIT © Sindre Sorhus