                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /网页定位导航特效

第二个for循环里，为什么items只能遍历到它的第二个元素，求大神帮忙看看代码错在哪儿?代码过多，删除了一部分

<!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>
    //注意掌握正则表达式
    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, "");
		}
	}
	function addClass(obj,cls){
        if(!hasClass(obj,cls)){
        obj.className +=" "+cls; 
        }
    }
	
    //定义getByClassName函数，让函数实现给对象增加class
    //注意传入参数对象、函数内部for循环的使用以及if判断语句中的条件的书写
    function getByClassName(obj,cls){
        var elements=obj.getElementsByTagName("*");
        var result=[];
        for(var j=0;j<elements.length;j++){
            if(elements[j].className==cls){
                result.push(elements[j]);
            }
        }
        return result;
    }
    //主要js
    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;
                }
            }
            if(currentId){
                for(var i=0;i<menus.length;i++){
                    var menu=menus[i];
                    var href=menu.href.split("#");
                    if(href[href.length-1]!=currentId){
                        removeClass(menu,"current");
                    }else{
                        addClass(menu,"current");
                    }
                }
            }
        }
    }	 				
      //请补充此处代码，给正确的menu下的a元素class赋值current
</script>
</head>
</html>