JavaScript 实现自定义右键菜单及坐标获取

<!doctype html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>demo</title>
    <style type="text/css">
      html{
        height:100%;
      }
      body{
        height:100%;
      }
      #mydiv{
        width:300px;
        height:300px;
        background-color: #ff7400;
      }
      #ctxMenu{
        background-color: #ff7400;
        list-style-type: none;
        position: absolute;
        padding:0px;
        border:1px solid #000;
        visibility: hidden;
      }
    </style>
  </head>
  <body>
    <div id="mydiv"></div>
    <h2 id="show"></h2>
    <input type="text"id="txt"><span id="help"></span>
    <ul id="ctxMenu">
      <li>上传</li>
      <li>下载</li>
      <li>新建</li>
      <li>取消</li>
    </ul>
    <script type="text/javascript">
      var $=function(id){
        return document.getElementById(id);
      };
      var h2=$("show");
      var ctx=$("ctxMenu");
      var txt=$("txt");
      var help=$("help");
      /*
      txt.onfocus=function(){
        help.innerHTML="请输入金额";
      }
      txt.onkeydown=function(event){
        help.innerHTML="";
        var code=event.keyCode;
        if(!(code>=48&&code<=57||code>=96&&code<=105||code==46||code==8||code==13||code==37||code==39||code==110||code==190)){
          event.preventDefault();
        }
      }
      */
      document.body.oncontextmenu=function(event){
        event.preventDefault();
        var x=event.pageX;
        var y=event.pageY;
        ctx.style.left=x+"px";
        ctx.style.top=y+"px";
        ctx.style.visibility="visible";
      }
      document.body.onclick=function(){
        ctx.style.visibility="hidden";
      }
      /*
      document.body.onmousemove=function(event){
        var x=event.pageX;
        var y=event.pageY;
        h2.innerHTML=x+":"+y;
      }
      */
      window.onbeforeunload=function(){
        var v=$("txt").value;
        if(v){
          return "";
        }
      }
      $("mydiv").onclick=function(){
        $("show").innerHTML="click";
      };
      $("mydiv").ondblclick=function(){
        $("show").innerHTML="dblclick";
      };
      $("mydiv").onmouseover=function(){
        $("show").innerHTML="mouseover";
        this.style.backgroundColor="#2d2d2d";
      };
      $("mydiv").onmouseout=function(){
        $("show").innerHTML="mouseout";
        this.style.backgroundColor="pink";
      }
    </script>
  </body>
</html>