JavaScript实现自定义右键菜单功能

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>右键菜单</title>
 <style type="text/css">
  *{
   margin: 0;
   padding: 0;
  }
  #menu{
   width: 254px;
   /*background-color: #ccc;*/
   font-size: 12px;
   position: fixed;
   top: 0px;
   left: 0px;
   /*height: 240px;*/
   /*padding-left: 26px;*/
   padding-top: 2px;
   border:1px solid #ccc;
   display: none;
  }
  #menu li{
   list-style: none;
   line-height: 25px;
   margin-left: -1px;
   padding-left: 26px;
  }
  #menu li:hover{
   background-color: #4281f4;
   color: #fff;
  }
 </style>
</head>
<body>
  <ul id="menu">
   <li>返回(B)</li>
   <li>前进(F)</li>
   <li>从新加载(R)</li>
   <li>另存为(A)</li>
   <li>打印(P)</li>
   <li>查看网页源代码(V)</li>
   <li>查看网页信息(I)</li>
   <li>审查元素(N)</li>
  </ul>
  <script type="text/javascript">
  var menu = document.getElementById("menu");

  document.oncontextmenu =function(e){
   var e = e ||window.event;//兼容
   console.log(e.clientX,e.clientY);
   console.log(e);
   //单击显示div
   menu.style.display = "block";
   //设置定义
   //判断鼠标坐标是否大于视口宽度-块本身宽度
   var cakLeft = (e.clientX > document.documentElement.clientWidth - menu.offsetWidth)?(document.documentElement.clientWidth - menu.offsetWidth):e.clientX;
   var cakTop = (e.clientY > document.documentElement.clientHeight - menu.offsetHeight)?(document.documentElement.clientHeight - menu.offsetHeight):e.clientY;
   menu.style.left = cakLeft + "px";
   menu.style.top = cakTop + "px";

  return false;
  }

   menu.onclick = function(e) {
  var e = e || window.event;
  e.cancelBubble = true;
  //阻止冒泡。
 }
  document.onclick = function() {
  menu.style.display = "none";
 }
  
  </script>
</body>
</html>