node.js event listener in another source file

Question

I am trying to design a scenario where on a particular event getting triggered, I wanted a few listeners to perform some task. Trying to also manage S.R.P of code, I want to have the listeners in a different source file. I want to know if this is possible using event Emitter. Does event emitter only work on a single source file?

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

exports.saveScheme = function (req, res) {  

var dal = dalFactory.createDAL(constants.SCHEME);
return new Promise.resolve(dal.PromiseSave(req.body))
    .then(function(data){
        var schemeId = data._id;

        em.addListener('FirstEvent', function (data) {
            console.log('First subscriber: ' + data);
        });
        em.emit('FirstEvent', 'Test event emitter');

    }).catch(function(error){
        console.log(error);
    }); 
};

My other source file is

var emitter = require('events').EventEmitter;
var em = new emitter();

//Subscribe FirstEvent
em.on('FirstEvent', function (data) {
    console.log('First subscriber: ' + data);
});

Answer 1

Every eventEmitter object you create is a new instance so events fired from the first one won't be triggered in the second, so the answer to your question is - no, it's not possible. However, there are other solutions:

I think the best one is to create a centralized common eventEmitter, like so:

//firstFile.js
var common = require('./common');
var commonEmitter = common.commonEmitter;

exports.saveScheme = function (req, res) {  

var dal = dalFactory.createDAL(constants.SCHEME);
return new Promise.resolve(dal.PromiseSave(req.body))
    .then(function(data){
        var schemeId = data._id;

        commonEmitter.addListener('FirstEvent', function (data) {
            console.log('First subscriber: ' + data);
        });
        commonEmitter.emit('FirstEvent', 'Test event emitter');

    }).catch(function(error){
        console.log(error);
    }); 
};



//secondFile.js
var common = require('./common');
var commonEmitter = common.commonEmitter;

//Subscribe FirstEvent
commonEmitter.on('FirstEvent', function (data) {
    console.log('First subscriber: ' + data);
});


//common.js
var events = require('events');
var em = new events.EventEmitter();
module.exports.commonEmitter = em;

But if you want the source file to "know" each other - You can do something like this:

//firstFile.js
var events = require('events');
var em = new events.EventEmitter();

exports.saveScheme = function (req, res) {  

var dal = dalFactory.createDAL(constants.SCHEME);
return new Promise.resolve(dal.PromiseSave(req.body))
    .then(function(data){
        var schemeId = data._id;

        em.addListener('FirstEvent', function (data) {
            console.log('First subscriber: ' + data);
        });
        em.emit('FirstEvent', 'Test event emitter');

    }).catch(function(error){
        console.log(error);
    }); 
};
exports.emitter = em;



//secondFile.js
var firstFile = require('./firstFile');
var firstFileEmitter = firstFile.emitter;

//Subscribe FirstEvent
firstFileEmitter.on('FirstEvent', function (data) {
    console.log('First subscriber: ' + data);
});