Creating custom event in JavaScript...

First, define custom event.

    var CustomEvent = function() {
        //name of the event
        this.eventName = arguments[0];
        var mEventName = this.eventName;

        //function to call on event fire
        var eventAction = null;

        //subscribe a function to the event
        this.subscribe = function(fn) 
        {
            eventAction = fn;
        };

        //fire the event
        this.fire = function(sender, eventArgs) 
        {
            if(eventAction != null) 
            {
                eventAction(sender, eventArgs);
            }
            else 
            {
                alert('There was no function subscribed to the ' + mEventName + ' event!');
            }
        };
    };

Then create an event handler.

    var myEvent = new CustomEvent("helloworld event");
    myEvent.subscribe(event_triggered);

    function event_triggered(sender, eventArgs)
    {
        alert("hello world");
    }

Now, the triggering part.

    ...
    if(typeof(myEvent) != "undefined")
    {
        myEvent.fire(null, { 
            message: 'you just witnessed the firing of a custom event called ' + this.eventName + '!'
        });
    }
    ...