event.srcElement.id为空

document.oncontextmenu = function (event)
{
var event = event || window.event;     

var clickID = event.srcElement.id+"";

}

clickID 为空，

原因：html代码：    <div id="XE1">
<img src="images/port_disable.png" width="40" height="35">
</div>

获取到的为image，加上parentElement即为XE1

解决方法：var event = event || window.event;     
var obj = event.srcElement || event.target;
var clickID = obj.parentElement.id+"";