event-done

Extension of EventEmitter which allows to pass callback that will be invoked when all listeners completed

Usage

1. We can have multiple listeners attached to the same event, but final callback will be called only once

   var EventDone = require('event-done').EventDone;
   var event = new EventDone();
    
   event.on('test', function (data, next) {
       console.log('I am listener one');
       next(null);
   });
    
   event.on('test', function (data, next) {
       console.log('I am listener two');
       next(null);
   });
    
   event.on('test', function (data, next) {
       console.log('I am listener three');
       setTimeout(next, 100);
   });
    
   event.emit('test', {some: 'data'}, function finish(error) {
       console.log('I am called only once after all three listeners');
       console.log('Error is empty:', error);
   });

2. Let's assume that one of listeners did not call it's callback. In this case final callback will be called with error of type EventDoneTimeoutError

   var EventDone = require('event-done').EventDone;
   var EventDoneTimeoutError = require('event-done').EventDoneTimeoutError;
   require('event-done').timeout = 100;
   console.log('Fallback timeout can be set to anything.',
       'Default is 30s and we set it to 100ms');
    
   var event = new EventDone();
    
   event.on('test', function (data, next) {
       console.log('I am listener one', 'Oops, I forgot to call "next"');
   });
    
   event.on('test', function (data, next) {
       console.log('I am listener two');
       next(null);
   });
    
   event.emit('test', {some: 'data'}, function finish(error) {
       console.log('I am called after 100ms "fallback" timeout');
       console.log('error is not empty and is instance if EventDoneTimeoutError:',
           error instanceof EventDoneTimeoutError);
   });

3. In case of any listener fails, final callback is instantly called with that error

   var EventDone = require('event-done').EventDone;
   var event = new EventDone();
    
   event.on('test', function (data, next) {
       console.log('I am listener one');
       next(new Error('OMFG!'));
   });
    
   event.on('test', function (data, next) {
       console.log('I am listener two',
           'I will still output this to console, but after final callback');
       next(null);
   });
    
   event.emit('test', {some: 'data'}, function finish(error) {
       console.log('I am called after first listener called');
       console.log('error is not empty and it is "OMFG!":',
           (error instanceof Error) && error.message === 'OMFG!');
   });