ee-first

What is ee-first?

The ee-first package is a utility for Node.js that allows you to wait for multiple EventEmitter or Stream instances to emit an event or error and then execute a callback. It is particularly useful when you need to listen for an event from multiple sources and want to take action only after the first one occurs.

What are ee-first's main functionalities?

Listening for the first event or error from multiple emitters

This feature allows you to pass an array of arrays, where each sub-array contains an EventEmitter instance followed by one or more event names. The callback function is then executed when the first event from any of the listed emitters is emitted.

const first = require('ee-first');

const stream1 = getSomeReadableStream();
const stream2 = getAnotherReadableStream();

const thunk = first([
  [stream1, 'end', 'error'],
  [stream2, 'end', 'error']
], function (err, ee, event, args) {
  // This function will be called when one of the streams emits 'end' or 'error'
  // `ee` is the event emitter that fired
  // `event` is the string name of the event that fired
  // `args` is an array of the arguments that were passed to the event
});

Other packages similar to ee-first

event-promise

The event-promise package provides a way to wait for an event to be emitted using promises. It is similar to ee-first in that it deals with events, but it works with individual emitters and events rather than a collection of them.

await-event

Await-event is another package that allows you to wait for an event to be emitted, but it is designed to be used with async/await syntax for a single EventEmitter. Unlike ee-first, it does not handle multiple emitters.

event-to-promise

Event-to-promise converts events to promises, similar to event-promise. It allows you to wait for an event on an EventEmitter, but it does not provide the functionality to listen to multiple emitters and act on the first event like ee-first does.

README

EE First

Get the first event in a set of event emitters and event pairs, then clean up after itself.

Install

$ npm install ee-first

API

var first = require('ee-first')

first(arr, listener)

Invoke listener on the first event from the list specified in arr. arr is an array of arrays, with each array in the format [ee, ...event]. listener will be called only once, the first time any of the given events are emitted. If error is one of the listened events, then if that fires first, the listener will be given the err argument.

The listener is invoked as listener(err, ee, event, args), where err is the first argument emitted from an error event, if applicable; ee is the event emitter that fired; event is the string event name that fired; and args is an array of the arguments that were emitted on the event.

var ee1 = new EventEmitter()
var ee2 = new EventEmitter()

first([
  [ee1, 'close', 'end', 'error'],
  [ee2, 'error']
], function (err, ee, event, args) {
  // listener invoked
})

.cancel()

The group of listeners can be cancelled before being invoked and have all the event listeners removed from the underlying event emitters.

var thunk = first([
  [ee1, 'close', 'end', 'error'],
  [ee2, 'error']
], function (err, ee, event, args) {
  // listener invoked
})

// cancel and clean up
thunk.cancel()