alert(arr[i-1])弹出undefined.这证明document.getElementById("pop"+arr[i-1])无效的
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
 <script type="text/javascript">
    function $(id){
return document.getElementById(id);
}
function navs(){
var arr = [1,2,3];
var nav = $("nav").getElementsByTagName("li");
for(var i=0; i<nav.length; i++){
if(i == arr[i-1]){
nav[i].onmouseover = function(){
alert(arr[i-1])
document.getElementById("pop"+arr[i-1]).style.display="";
}
nav[i].onmouseout = function(){
document.getElementById("pop"+arr[i-1]).style.display="none";
}
}
}
}
window.onload = navs;

   </script>
   <style type="text/css">
    *{margin:0;padding:0;}
.wrap{margin:55px auto;width:600px;}
a{text-decoration: none}
ul{list-style:none outside none}
body{font-family:Arial, Helvetica, sans-serif;font-size:12px;font-weight:bold}
.nav li{float: left;width:105px;height:25px;}
.nav li.cur{ background:url(images/m2-act.gif) no-repeat;}
.pop{clear: both;background:pink;height:30px;}
.pop li{float: left;width:100px;height:35px;line-height:35px;}
   </style>
</head><body>
<div class="wrap">
<div class="nav" id="nav">
<ul>
<li><a href="">HOME</a></li>
<li><a href="">ABOUT US</a></li>
<li><a href="">SERVICES</a></li>
<li><a href="">SUPPORT</a></li>
<li><a href="">CONTACTS</a></li>
</ul>
</div>

<ul class="pop" id="pop1" style="display:none">
<li><a href="">公司概况</a>| </li>  
<li><a href="">资质荣誉</a>|</li>  
<li><a href="">媒体报道</a></li>
</ul>
<ul class="pop" id="pop2" style="display:none">
<li><a href="">公司概况</a>| </li>  
<li><a href="">资质荣誉</a>|</li>  
<li><a href="">媒体报道</a></li>
</ul>
<ul class="pop" id="pop3" style="display:none">
<li><a href="">公司概况</a>| </li>  
<li><a href="">资质荣誉</a>|</li>  
<li><a href="">媒体报道</a></li>
</ul>
</div>
</body>
</html>

解决方案 »

  1.   

    for(var i=0; i<nav.length; i++){
                    if(i == arr[i-1]){
                        nav[i].onmouseover = function(){
                        alert(arr[i-1])
    i-1=-1???
    i从0开始,0-1=-1,
    数组下标不能为负
      

  2.   

    ABOUT US
    SERVICES
    SUPPORT
    我只想让这3个下拉菜单
      

  3.   

    <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
     <script type="text/javascript">
        $(function(){
    var t;
    $("#nav ul li").each(function(index){
    $(this).mouseover(function(){
    $("#pop"+index).show()
    }).mouseout(function(){
    t = $("#pop"+index).hide()
    })
    })
    })    
     </script>
    延迟的机制就自己写一下吧。jq还是方便啊
      

  4.   

    改一下吧 
    你这样写每次都跳出 alert(arr[6-1])
    应该是 1-3 而不是 1-5 ,所以5永远是未定义滴
      

  5.   

    js 闭包 for(var i=0; i<nav.length; i++){
                    if(i == arr[i-1]){
                     ( function(i){
                           nav[i].onmouseover = function(){
                        alert(arr[i-1])
                            document.getElementById("pop"+arr[i-1]).style.display="";
                        }
                        nav[i].onmouseout = function(){
                            document.getElementById("pop"+arr[i-1]).style.display="none";
                        }
                      })(i);
                    }
                }
      

  6.   

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml">
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
    <title>无标题文档</title>
     <script type="text/javascript">
               function $(id){
                return document.getElementById(id);
            }
            function navs(){
                var arr = [1,2,3];
                var nav = $("nav").getElementsByTagName("li");
                for(var i=0; i<nav.length; i++){
                    if(i == arr[i-1]){
                        nav[i].onmouseover = function(){
                               return function(){
                                  alert(arr[i-1])
                            `   ` document.getElementById("pop"+arr[i-1]).style.display="";
                              }
                        }(i);
                        nav[i].onmouseout = function(){
                               return function(){
                                 document.getElementById("pop"+arr[i-1]).style.display="none";                          }
                        }(i);
                    }
                }
            }
            window.onload = navs;
            
       </script>
       <style type="text/css">
           *{margin:0;padding:0;}
        .wrap{margin:55px auto;width:600px;}
        a{text-decoration: none}
        ul{list-style:none outside none}
        body{font-family:Arial, Helvetica, sans-serif;font-size:12px;font-weight:bold}
        .nav li{float: left;width:105px;height:25px;}
        .nav li.cur{ background:url(images/m2-act.gif) no-repeat;}
        .pop{clear: both;background:pink;height:30px;}
        .pop li{float: left;width:100px;height:35px;line-height:35px;}
       </style>
    </head><body>
    <div class="wrap">
        <div class="nav" id="nav">
            <ul>
                <li><a href="">HOME</a></li>
                <li><a href="">ABOUT US</a></li>
                <li><a href="">SERVICES</a></li>
                <li><a href="">SUPPORT</a></li>
                <li><a href="">CONTACTS</a></li>
            </ul>
        </div>
        
                    <ul class="pop" id="pop1" style="display:none">
                        <li><a href="">公司概况</a>| </li>  
                        <li><a href="">资质荣誉</a>|</li>  
                        <li><a href="">媒体报道</a></li>
                    </ul>
                    <ul class="pop" id="pop2" style="display:none">
                        <li><a href="">公司概况</a>| </li>  
                        <li><a href="">资质荣誉</a>|</li>  
                        <li><a href="">媒体报道</a></li>
                    </ul>
                    <ul class="pop" id="pop3" style="display:none">
                        <li><a href="">公司概况</a>| </li>  
                        <li><a href="">资质荣誉</a>|</li>  
                        <li><a href="">媒体报道</a></li>
                    </ul>
    </div>
    </body>
    </html>