Some java script snippets - Event Handler - part 1

This is the first part of a sample event handler. We will see the declaration here

Note: Copy the code into notepad or someother custom editor for more legibility

     var HANDLER = new EventHandler();
/**************************************************************************
Event Handler definition begins
**************************************************************************/
/* Cross browser event handler, that allows multiple handlers to handle the event */
function EventHandler () {    
    /* This is an array of eventHandler arrays, essentially a hashMap 
    defined using associative arrays.
    Example content at run time would be
    events["onload"] = ["adjustDiv", "centerAlignText"...];
    where righthand side is a array of event Handling functions
    */
    var eHandler = this;
    eHandler.events = [];
    
    function getHandlersForEventType(aEventType) {
        /* if this is the first time we are listening the event,
        create handlers array
        */        
        if(eHandler.events[aEventType]==undefined) {
            eHandler.events[aEventType] = [];
        }
        return eHandler.events[aEventType];
    }
    
    function detectEvent(event) {
        // grab the event object (IE uses a global event object)
        event = event || ((this.ownerDocument || this.document || this).parentWindow || window).event;
        return event;
    }
    
    function registerEventHandlerWithType(aEventType, handlerFnc){        
        var handlers = getHandlersForEventType(aEventType)
        handlers[handlerFnc] = handlerFnc;        
    }
    
    function unregisterEventHandlerWithType(aEventType, handlerFnc){
        var handlers = getHandlersForEventType(aEventType);
        /* if this handler is not registered*/
        if(handlers[handlerFnc]==undefined) {
            return;
        }    
        delete handlers[handlerFnc];    
    }
    
    function handleEvent(aEvent){
        aEvent = detectEvent(aEvent);        
        var handlers = getHandlersForEventType(aEvent.type);
        var diagMsg = "";
        for(var handle in handlers){     
            // construct the method call from the function name and pass parameter            
            eval(handle)(aEvent);
        }
        /* stop the event bubbling now, this ensures browser compatibility */
        if(typeof aEvent.cancelBubble != undefined){            
            // IE event model
            aEvent.cancelBubble = true;
        }        
        if (aEvent.stopPropagation){            
            // Gecko event model
            aEvent.stopPropagation();
        }
    }
    
    return {
        /* public methods that are being exposed */
        registerEventHandlerWithType: registerEventHandlerWithType,        
        unregisterEventHandlerWithType: unregisterEventHandlerWithType,
        handleEvent: handleEvent        
    }
}

/**************************************************************************
Event Handler definition ends
**************************************************************************/

function observeEvent(aEvent){    
    HANDLER.handleEvent(aEvent);
}