问个很简单的js程序有关问题

问个很简单的js程序问题
js代码中 两次alert(month[i]); 第一次就能输出 我想要的结果，第二次就是undefine了，我在想是不是作用域的问题。。 让那个onmouseover= function形成的闭包 所以里面就读取不到i的值了啊？ 请教高手 请改怎么改改。。。

JScript code

function monthList(data){    var month = new Array(data.January,data.February,data.March,data.April,data.May,data.June,data.July,data.August,data.September,data.October,data.November,data.December);//创建数组    var nianLi = document.getElementById("nianLi").getElementsByTagName("li");    var conTent = document.getElementById("content");    for(var i=0;i<month.length;i++){                //鼠标浮动到1-12月以后 弹出相应数字        nianLi[i].index = i+1;                alert(month[i]);        nianLi[i].onmouseover = function(){                        alert(month[i]);            conTent.innerHTML = ""+this.index+"月"+month[i];        }        nianLi[i].onmouseout = function(){            conTent.innerHTML = "";        }        }};monthList({    January:"出去玩",    February:"玩什么",    March:"玩玩玩",     April:"哈哈",     May:"呵呵",     June:"嘿嘿",     July:"嘻嘻",     August:"吼吼",     September:"好好玩",     October:"玩玩玩",     November:"呵呵呵",     December:"嘻嘻嘻"});

HTML code

<div class="nianLi">    <ul id="nianLi">        <li>1月</li>        <li>2月</li>        <li>3月</li>        <li>4月</li>        <li>5月</li>        <li>6月</li>        <li>7月</li>        <li>8月</li>        <li>9月</li>        <li>10月</li>        <li>11月</li>        <li>12月</li>    </ul>    <div style="clear:left"></div>    <div id="content"></div></div>

CSS code

ul,li{ padding:0; margin:0; list-style:none;}.nianLi{ width:162px; height:216px; position:relative;}.nianLi ul li{ width:50px; height:50px; float:left; text-align:center; font:100 12px/50px "\5B8B\4F53"; border:1px solid #000; margin:0 2px 2px 0; cursor:pointer;}#content{ position:absolute; width:80px; height:80px; border:1px solid #000; left:200px; top:0; padding:10px;}

JScript code

 nianLi[i].index = i+1;//和这个一样用呀，你这不是自己已经用了么？？ nianLi[i].month=month[i];//        nianLi[i].onmouseover = function(){            conTent.innerHTML = this.index+'月'+this.month;        }
[解决办法]
这样可以

function monthList(data){
   var month = new Array(data.January,data.February,data.March,data.April,data.May,data.June,data.July,data.August,data.September,data.October,data.November,data.December);//创建数组
   var nianLi = document.getElementById("nianLi").getElementsByTagName("li");
   var conTent = document.getElementById("content");
   for(var i=0;i<month.length;i++){
      
       //鼠标浮动到1-12月以后 弹出相应数字
       nianLi[i].index = i+1;
               alert(month[i]);
       (function(j) {
nianLi[i].onmouseover = function(){
                       alert(month[j]);alert(j);
           conTent.innerHTML = ""+this.index+"月"+month[j];
       } 
})(i);

       nianLi[i].onmouseout = function(){
           conTent.innerHTML = ""; 
 
       }
  
   }
};

monthList({
   January:"出去玩",
   February:"玩什么",
   March:"玩玩玩",  
   April:"哈哈",  
   May:"呵呵",  
   June:"嘿嘿",  
   July:"嘻嘻",  
   August:"吼吼",  
   September:"好好玩",  
   October:"玩玩玩",  
   November:"呵呵呵",  
   December:"嘻嘻嘻"
});

解释一下

这是闭包的问题

for(var i=0;i<month.length;i++){
      
       //鼠标浮动到1-12月以后 弹出相应数字
       nianLi[i].index = i+1;
               alert(month[i]);
       nianLi[i].onmouseover = function(){
                       alert(month[i]);
           conTent.innerHTML = ""+this.index+"月"+month[i];
       }
       nianLi[i].onmouseout = function(){
           conTent.innerHTML = "";
       }
  
   }

这样nianLi[i].onmouseover = function(){
                       alert(month[i]);
           conTent.innerHTML = ""+this.index+"月"+month[i];
       }形成了闭包，当访问外层函数i时alert(month[i])，当执行到nianLi[11].onmouseover = function(){
                       alert(month[11]);之后，再执行for循环中的i++，这时i=12，所以是undefined啊
[解决办法]
探讨


nianLi[i].onmouseover = (function(i){
      return function(){
                       alert(month[i]);
           conTent.innerHTML = ""+this.index+"月"+month[i];
       }
}(i);