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I am trying to emit from one EventEmitter to another EventEmitter, or find an alternative solution. The code below doesn't function.

Multiple emitter example

var events = require('events');

var eventEmitterOne = new events.EventEmitter();
var eventEmitterTwo = new events.EventEmitter();

eventEmitterTwo.on('fireEvent', function() {
     console.log('event fired');
});

eventEmitterOne.emit('fireEvent');

I'm looking to find out if the following is possible and whats changes I would need to make to the following code to make it functional. Or is there another way of emitting events across multiple emitters. Thanks for your time.

I am trying to emit from one EventEmitter to another EventEmitter, or find an alternative solution. The code below doesn't function.

Multiple emitter example

var events = require('events');

var eventEmitterOne = new events.EventEmitter();
var eventEmitterTwo = new events.EventEmitter();

eventEmitterTwo.on('fireEvent', function() {
     console.log('event fired');
});

eventEmitterOne.emit('fireEvent');

I'm looking to find out if the following is possible and whats changes I would need to make to the following code to make it functional. Or is there another way of emitting events across multiple emitters. Thanks for your time.

• javascript
• node.js
• eventemitter

Share Improve this question Follow asked Jul 12, 2013 at 18:04 Gerard DownesGerard Downes 6431111 silver badges2525 bronze badges 1

• 2 EventEmitters are independent from each other. They can have multiple listeners on the same event, but each emitter will emit its events only to its listeners, not to other emitters. However, you can add listeners automatically to multiple emitters by listening to the newListener event. – Zeta Commented Jul 12, 2013 at 18:08

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2 Answers 2

Sorted by: Reset to default 8

The issue is that the two EventEmitters are separate objects.

When you call:

var eventEmitterOne = new events.EventEmitter();
var eventEmitterTwo = new events.EventEmitter();

You’re creating two separate EventEmitter objects. This means that when you emit events to one, you cannot trigger them by firing events on the other.

There’s nothing wrong with your code, just your understanding of what should be happening.

The way I like to do this is by wrapping things in my own EventEmitter module. This way I have a "global" emitter object, with some simple function wrappers for emitting and registering events. This allows many different modules to share the same set of events, register events for other modules to fire, and so on.

var eventEmitter = new (require('events').EventEmitter)();

function emitEvent(str) {
    'use strict';
    eventEmitter.emit(str);
}

function registerEvent(str, callback) {
    'use strict';
    eventEmitter.on(str, callback);
}

function registerEventOnce(str, callback) {
    'use strict';
    eventEmitter.once(str, callback);
}

exports.emitEvent = emitEvent;
exports.registerEvent = registerEvent;
exports.registerEventOnce = registerEventOnce;

Just throw the above code into a file called EventFileName.js. And its use is very simple.

var customEventEmitter = require('./EventFileName');
customEventEmitter.registerEvent('fireEvent', someCallback);
customEventEmitter.emitEvent('fireEvent');

The other answer cannot emit event with arguments. So here is the improvement:

'use strict';

var eventEmitter = new (require('events').EventEmitter)();

function emitEvent(...args) {
    eventEmitter.emit(...args);
}

function registerEvent(str, callback) {
    eventEmitter.on(str, callback);
}

function registerEventOnce(str, callback) {
    eventEmitter.once(str, callback);
}

exports.emit = emitEvent;
exports.on = registerEvent;
exports.once = registerEventOnce;

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