Event Delegation by Stedia and the MooTools Dev Team

README.js

// basic usage:

$('myParentElement').relayEvents({
    
    'a.menuitem':{
        'click': function(e){}
    },
    
    'input[name=phone]':{
        'keydown': function(e){},
        'keypress': function(e){}
    }
    
});

relayEvents.moo.js

/*

Event Delegation - really powerfull, if you can understant why :-)    
    
License: MIT-style license.
Copyright: Copyright (c) 2008 Daniel Steigerwald, daniel.steigerwald.cz

Example: http://daniel.steigerwald.cz/demos/delegated/default.htm

*/
(function(){
	
	function check(e, selector, fn){
		var target    = e.target,
			els       = this.getElements(selector),
			isOverOut = /^(mouseover|mouseout)$/.test(e.type);
		
		for (var i = els.length; i--; ){
			var el = els[i];
			if (el == target || el.hasChild(target)){
				if (isOverOut && !checkOverOut.call(el, e)) return;
				fn.call(el, e, el);
				return;
			}
		}
	}
	
	function checkOverOut(e){
		var    related = e.relatedTarget;
		return related         == undefined 
			|| related        !== false
			&& $type(this)    !=  'document'
			&& related        !=  this
			&& related.prefix !=  'xul'
			&& !this.hasChild(related);
	}
	
	Element.Properties.relayedEvents = {
		set: function(obj){
			this.relayEvents(obj);
		}
	};
	
	Element.implement({
		
		relayEvent: function(selector, type, fn){
			type = { mouseenter: 'mouseover', mouseleave: 'mouseout'}[type] || type;
			
			var revents = this.retrieve('$moo:revents');
			if (!revents) this.store('$moo:revents', revents = {});
			
			var sel = revents[selector] = revents[selector] || {};
			sel[type] = sel[type] || [];
			
			var fn = check.bindWithEvent(this, [selector, fn]);
			sel[type].push(fn);
			
			return this.addEvent(type, fn);
		},
		
		relayEvents: function(selector, events){
			if (/^(hash|object)$/.test($type(selector)))
				for (var sel in selector) this.relayEvents(sel, selector[sel]);
			else
				for (var type in events) this.relayEvent(selector, type, events[type]);
			return this;
		},
		
		unrelayEvents: function(selector){
			var events = this.retrieve('$moo:revents');
			if (events && events[selector]){
				for (var type in events[selector]){
					events[selector][type].each(function(fn){
						this.removeEvent(type, fn);
					}, this);
				}
			}
			return this;
		}
		
	});
	
})();