promise-once-events

This module provides promisified version of standard EventEmitter class, except that once method returns Promise object which is fulfilled when emit method is called.

Requirements

This module requires Node >= 4. For Node < 6 --harmony flag is required.

Installation

npm install promise-once-events

Usage

promise-once-events can be a base class for custom event emitter.

const PromiseOnceEvents = require('promise-once-events')
 
class MyEmitter extends PromiseOnceEvents {}
 
const emitter = new MyEmitter()

Method once returns Promise object which is fulfilled when emit method is called and then result is an Arguments object which contains arguments from emit method.

// As promise
emitter.once('event').then(result => {
  // result is object Arguments
  console.log('an event occurred with arguments:', result)
})
 
emitter.emit('event', 'a', 'b')

It also works with async/await syntax:

// As promise
const result = await emitter.once('event')
// result is object Arguments
console.log('an event occurred with arguments:', result)

If the last argument for once method is a callback then it works as for original EventEmitter.once method.

// With callback
emitter.once('event', (a, b) => {
  console.log('an event occurred with arguments:', [a, b])
})
 
emitter.emit('event', 'a', 'b')

Overriding EventEmitter

PromiseOnceEvents can be used as a replacement for EventEmitter for existing objects.

Example:

const readable = fs.createReadStream(process.argv[2] || __filename)
 
readable.once = PromiseOnceEvents.prototype.once
 
readable.on('data', (chunk) => {
  console.log(`Received ${chunk.length} bytes of data.`)
})
 
await readable.once('end')
console.log('There will be no more data.')

Promise

This module uses any-promise and any ES6 Promise library or polyfill is supported.

Ie. bluebird can be used as Promise library for this module, if it is registered before.

require('any-promise/register/bluebird')
const PromiseOnceEvents = require('promise-once-events')

License

MIT

promise-once-events