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{Event-Emitter}

The Question

Your REACTO question today is to implement a familiar Javascript concept:

the EventEmitter. It works like this:

You can create an EventEmitter:

var myEventEmitter = new EventEmitter();

And you can register listeners to different event strings with an on method:

myEventEmitter.on('anImportantEvent', function (eventDetails) {
  console.log('Something important just happened!', eventDetails);
});

These listeners get called when the created event emitter emits the event with related data:

myEventEmitter.emit('anImportantEvent', { location: 'Fullstack' });

You can also unregister a listener using a removeListener method:

var fn = function () {
  console.log('Cool, my event happened!');
};

// Listener is attached.
myEventEmitter.on('prestoBango', fn); 

// Listener is no longer attached and has moved on with its life.
myEventEmitter.removeListener('prestoBango', fn); 

 Overview of full functionality

var superbowl = new EventEmitter();

var cheer = function (data) {
  console.log('RAAAAAHHHH!!!! Go ' + data.scoringTeam);
};

var jeer = function (data) {
  console.log('BOOOOOO ' + data.scoringTeam);
};

superbowl.on('touchdown', cheer);
superbowl.on('touchdown', jeer);

superbowl.emit('touchdown', { scoringTeam: 'Patriots' }); 
// Both cheer and jeer are called with data.

superbowl.removeListener('touchdown', jeer);

superbowl.emit('touchdown', { scoringTeam: 'Seahawks' }); 
// Only cheer is called.

Answer

var EmmieEmitter = function () {
    this.events = {};
};

EmmieEmitter.prototype.emmieOn = function (eventStr, fn) {
    if (!this.events[eventStr]) {
        this.events[eventStr] = [];
    }

    this.events[eventStr].push(fn);

};

EmmieEmitter.prototype.emmieEmit = function (eventStr, eventData) {

    if (!this.events[eventStr]) {
        return;
    }

    this.events[eventStr].forEach(function (fn) {
        fn(eventData);
    });

};

EmmieEmitter.prototype.emmieRemoveListener = function (eventStr, fn) {

    var eventFns = this.events[eventStr];

    if (!eventFns) return;

    var i = eventFns.indexOf(fn);

    if (i === -1) return;

    eventFns.splice(i, 1);

};

1. Creating the constructor function

var EmmieEmitter = function () {
    this.events = {};
};

2. adding listeners

EmmieEmitter.prototype.emmieOn = function (eventStr, fn) {
    if (!this.events[eventStr]) {
        this.events[eventStr] = [];
    }

    this.events[eventStr].push(fn);

};

3. Emitting

EmmieEmitter.prototype.emmieEmit = function (eventStr, eventData) {

    if (!this.events[eventStr]) {
        return;
    }

    this.events[eventStr].forEach(function (fn) {
        fn(eventData);
    });

};

4. Remove Listeners

EmmieEmitter.prototype.emmieRemoveListener = function (eventStr, fn) {

    var eventFns = this.events[eventStr];

    if (!eventFns) return;

    var i = eventFns.indexOf(fn);

    if (i === -1) return;

    eventFns.splice(i, 1);

};

Conclusion  

EMIT ALLLLL THE EVENTSSSS

REPL