A simple event emitter class.

EventEmitter.js

var EventEmitter = function(){
    var events = {};

    this.on = function(name, callback){
        name = name.toLowerCase();
        events[name] = events[name] || [];
        events[name].push(callback);

        return this;
    };

    this.off = function(name, callback){
        name = name.toLowerCase();
        if (name in events === false) return this;
        events[name].splice(events[name].indexOf(callback), 1);
        return this;
    };

    this.once = function(name, callback){
        var that = this;
        function disposable(){
            that.off(name, disposable);
            callback.apply(that, arguments);
        }

        this.on(name, disposable);
        
        return this;
    };

    this.trigger = function(name){
        var that = this,
            args = arguments;
        
        name = name.toLowerCase();

        if (name in events === false) return this;
        events[name].forEach(function(fn){
            fn.apply(that, [].slice.call(args, 1));
        });
        
        return this;
    };

    this.asyncTrigger = function(name){
        var args = arguments,
            that = this;
        setTimeout(function(){
            that.trigger.apply(that, args);
        }, 0);
        
        return this;
    };
};