请大神帮忙看一下代码问题出在哪
字数不够 ，我把后面的HTML删了
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
<title>地狗购物网——网页定位导航效果</title>
<style>
* {
margin: 0;
padding: 0;
}
body {
font-size: 12px;
line-height: 1.7;
}
li {
list-style: none;
}
#content {
width: 800px;
margin: 0 auto;
padding: 20px;
}
#content h1 {
color: #0088bb;
}
#content .item {
padding: 20px;
margin-bottom: 20px;
border: 1px dotted #0088bb;
}
#content .item h2 {
font-size: 16px;
font-weight: bold;
border-bottom: 2px solid #0088bb;
margin-bottom: 10px;
}
#content .item li {
display: inline;
margin-right: 10px;
}
#content .item li a img {
width: 230px;
height: 230px;
border: none;
}
#menu {
position: fixed;
top: 100px;
left: 50%;
margin-left: 400px;
width: 80px;
}
#menu ul li a {
display: block;
margin: 5px 0;
font-size: 14px;
font-weight: bold;
color: #333;
width: 80px;
height: 50px;
line-height: 50px;
text-decoration: none;
text-align: center;
}
#menu ul li a:hover,
#menu ul li a.current {
color: #fff;
background: #0088bb;
}
/*ie6 hack*/
* html, * html body {
background-image: url(about:blank);
background-attachment: fixed;
}
* html #menu {
/*position: fixed;*/
position: absolute;
top: expression(((e=document.documentElement.scrollTop)?e:document.body.scrollTop)+100+'px');
}
</style>
<script>
//定义getByClassName函数，让函数实现根据class name获取对象并返回
// function getByClassName( obj, cls){
// var elements = obj.getElementsByTagName("*");
// var result = [];
// for (var i = 0;i<elements.length;i++){
// if(elements[i].className == cls ){
// result.push(elements[i]);
// }
// }
// return result;
// }
// function hasClass( obj, cls ){
// return obj.className.match(new RegExp("(\\s|^)" + cls + "(\\s|$)"));
// }
// function removeClass( obj, cls ){
// if( hasClass( obj, cls )){
// //remove
// var reg = new RegExp("(\\s|^)" + cls + "(\\s|$)");
// obj.className = obj.className.replace(reg, "");
// }
// }
// //定义getByClassName函数，让函数实现给对象增加class
// function addClass( obj, cls ){
// if( !hasClass( obj, cls )){
// obj.className += " " + cls;
// }
// }
//zhengque
function getByClassName(obj, cls){
var elements = obj.getElementsByTagName("*");
var result = [];
for(var i = 0; i < elements.length; i++){
if(elements[i].className == cls){
result.push(elements[i]);
}
}
return result;
}
function hasClass( obj, cls ){
return obj.className.match(new RegExp("(\\s|^)" + cls + "(\\s|$)"));
}
function removeClass( obj, cls ){
if( hasClass( obj, cls )){
//remove
var reg = new RegExp("(\\s|^)" + cls + "(\\s|$)");
obj.className = obj.className.replace(reg, "");
}
}
//定义getByClassName函数，让函数实现给对象增加class
function addClass(obj, cls){
if(!hasClass(obj, cls)){
obj.className += " " + cls;
}
}
window.onload = function(){
window.onscroll = function(){
var top = document.documentElement ? document.documentElement.scrollTop : document.body.scrollTop;
var menus = document.getElementById("menu").getElementsByTagName("a");
var items = getByClassName(document.getElementById("content"), "item");
var currentId = "";
for ( var i=0; i< items.length; i++ ){
var _item = items[i];
var _itemTop = _item.offsetTop;
if( top > _itemTop - 200 ){
currentId = _item.id;
} else {
break;
}
}
//请补充此处代码，给正确的menu下的a元素class赋值current
// if(currentId){
// for(var j = 0; j < menus.length; j++){
// var _menu = menus[j];
// var _href = _menu.href.split("#");
// if(_href[_href.length - 1] != currentId){
// removeClass(_menu, "current");
// } else {
// addClass(_menu, "current");
// }
// }
// }
//zhengque
if( currentId){
for (var j = 0;j < menus.length; j++){
var _menu = menus[j];
var _href = _menu.href.split("#");
if( _href[_href.length - 1] != currentId){
removeClass( _menu, "current");
}else{
addClass( _menu, "current");
}
}
}
}
}
</script>
</head>
<body>
<div id="menu">
<ul>
