js实现浏览器右键菜单，屏蔽默认菜单

<div id="mouse" style="width:500px;height:200px;background:#E8FFE8;border:2px solid #336699;"></div><div id="menu" style="display:none; position: absolute; color:red; border-radius: 3px;background-color: #666;">  <div style="padding:6px 6px 6px 6px;">    <a href="http://www.baidu.com">撤回消息</a>   </div></div><script>function bindMouseEvent(el){    var args = [].slice.call(arguments),    el = el || document;    args[0] = function(){},    args[1] = args[1] || args[0],    args[2] = args[2] || args[0],    args[3] = args[3] || args[0],    el.onmousedown = function(e){        e = e || window.event;        var button = e.button;        if ( !e.which && isFinite(button) ) {            e.which  = [0,1,3,0,2,0,0,0][button];         }        args[e.which](e);    }}var el = document.getElementById("mouse");var ex = document.getElementById("explanation");var menu = document.getElementById("menu");var left = function(){    menu.style.display = 'none';}var middle = function(){    menu.style.display = 'none';}var right = function(ev){    var ev= ev || event;    var scrollTop=document.documentElement.scrollTop || document.body.scrollTop;          menu.style.left = ev.clientX+scrollTop+'px';    menu.style.top = ev.clientY+scrollTop+'px';    menu.style.display = 'block';}bindMouseEvent(el,left,middle,right);document.oncontextmenu=function(ev){   return false;    //屏蔽右键菜单}</script>