阻止事件冒泡

<div style="height:30px;line-height:30px;background:#FF0;text-align:center;" id="zz"><a href="http://www.baidu.com">阻止事件冒泡</a></div>
    <script type="text/javascript">
        var $ = function(id){
                return document.getElementById(id);
            }
            
        $('zz').onclick = function(e){
                $('zz').innerHTML += "，事件已经点击了！";
                var e = e||window.event;
                    if (e.stopPropagation)
                    {
                        
                        e.stopPropagation();    // 阻止冒泡
                        e.preventDefault();        // 阻止默认事件
                    }
                    else
                    {
                        e.cancelBubble =true;    // 阻止冒泡
                        e.returnValue = false;    // 阻止默认事件
                    }
                    
            }
        document.documentElement.onclick = function(e){
                $('zz').innerHTML += "，冒泡没阻止成功！";
            }
    </script>