js事件冒泡与阻止冒泡

<div id="dv">
		<div id="dv1">
			<div id="dv2"></div>
			
		</div>
		
	</div>
	</body>
	
	<script>
		function mm(id){
			return document.getElementById(id);
		}
		//事件冒泡
		mm("dv").onclick=function(e){
		
		console.log(e.target);	
		} 
		mm("dv1").onclick=function(){
		console.log(this.id);	
		//阻止事件冒泡
		
		window.event.cancelBubble=true;
		}
		
		mm("dv2").onclick=function(e){
		console.log(this.id);
		//不支持ie8浏览器
		e.stopPropagation();
		}
	</script>