eventEmitterExample.js

/* Polyfill indexOf. */
var indexOf;

if (typeof Array.prototype.indexOf === 'function') {
    indexOf = function (haystack, needle) {
        return haystack.indexOf(needle);
    };
} else {
    indexOf = function (haystack, needle) {
        var i = 0, length = haystack.length, idx = -1, found = false;

        while (i < length && !found) {
            if (haystack[i] === needle) {
                idx = i;
                found = true;
            }

            i++;
        }

        return idx;
    };
};


/* Polyfill EventEmitter. */
var EventEmitter = function () {
    this.events = {};
};

EventEmitter.prototype.on = function (event, listener) {
    if (typeof this.events[event] !== 'object') {
        this.events[event] = [];
    }

    this.events[event].push(listener);
};

EventEmitter.prototype.removeListener = function (event, listener) {
    var idx;

    if (typeof this.events[event] === 'object') {
        idx = indexOf(this.events[event], listener);

        if (idx > -1) {
            this.events[event].splice(idx, 1);
        }
    }
};

EventEmitter.prototype.emit = function (event) {
    var i, listeners, length, args = [].slice.call(arguments, 1);

    if (typeof this.events[event] === 'object') {
        listeners = this.events[event].slice();
        length = listeners.length;

        for (i = 0; i < length; i++) {
            listeners[i].apply(this, args);
        }
    }
};

EventEmitter.prototype.once = function (event, listener) {
    this.on(event, function g () {
        this.removeListener(event, g);
        listener.apply(this, arguments);
    });
};














































// create an emitter instance
var emitter = new EventEmitter();


// Attach a listener - when this eventName is fired from the emitter, run this function/action
emitter.on("hello", function() {
    console.log("world");
});

// And again
emitter.on("hello", function() {
    console.log("world1");
});

// Fire the event (AKA tell any listeners that this "thing" happened and run their function/action)
emitter.emit("hello");

// Wait a second before firing the event
setTimeout(function() {
    emitter.emit("hello");
}, 1000);


// A Dog class that fires out an event when the speak method is run
function Dog() {
    this.speak = function() {
        emitter.emit("hello");
    };
}

// Create a dog and tell it to speak after a second
setTimeout(function() {
    new Dog().speak();
}, 1000);


// Toy version/example of our future state - we'll initialize an instance and pass it into our UI
function State() {
    this._emitter = new Emitter();
}

State.prototype.on = function(eventName, fn) {
      this._emitter.on(eventName, fn);
};

new State().on("event", function() {});