<div id="p_box" onclick="a()">
<div id=p_cont>
</div>
</div>

<div id="p_box" onclick="a()">
<div id="p_cont" onclick="stopBubble(this.id)">
</div>
</div>
function a(){
//這里是a事件的代碼
}
function stopBubble(e) {
if (e && e.stopPropagation) {//非IE瀏覽器
　　e.stopPropagation();
}
else {//IE瀏覽器
window.event.cancelBubble = true;
}
}