JavaScript 实现自定义鼠标右键菜单

<html>
 <head>
  <meta charset="gb2312" />
  <title></title>
  <style>
   #menu{
    border:solid 1px gray;
    width:100px;
    display:none;
    position:absolute;
    background-color:ghostwhite;
    margin: 0;
    padding: 0;
    list-style-type: none;
   }
   #menu>li{
    border-bottom: dashed 1px gray;
   }
  </style>
  <script type="text/javascript">
  window.onload=function(){
   var oUl=document.getElementById('menu');
    document.oncontextmenu=function(ev){
     var oEvent=ev||event;
     //一定要加px，要不然chrom不认
     oUl.style.top=oEvent.clientY+'px';
     oUl.style.left=oEvent.clientX+'px';
     oUl.style.display='block';
     return false;
    }
    document.onclick=function(){
     oUl.style.display='none';
    }
  };
  </script>
 </head>
 <body>
<ul id="menu">
 <li><a href="//www.jb51.net/" target="_blank">本站</a></li>
 <li><a href="//www.jb51.net/" target="_blank">本站</a></li>
 <li><a href="//www.jb51.net/" target="_blank">本站</a></li>
 <li><a href="//www.jb51.net/" target="_blank">本站</a></li>
</ul>
 </body>
</html>