                        課程
                    
                        /前端開發(fā)
                        
                            /JavaScript
                        
                        /網(wǎng)頁(yè)定位導(dǎo)航特效

第二個(gè)for循環(huán)里，為什么items只能遍歷到它的第二個(gè)元素，求大神幫忙看看代碼錯(cuò)在哪兒?代碼過(guò)多，刪除了一部分

<!DOCTYPE?html>
<html>
<head>
<meta?charset="utf-8"/>
<title>地狗購(gòu)物網(wǎng)——網(wǎng)頁(yè)定位導(dǎo)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>
????//注意掌握正則表達(dá)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;?
????????}
????}
	
????//定義getByClassName函數(shù)，讓函數(shù)實(shí)現(xiàn)給對(duì)象增加class
????//注意傳入?yún)?shù)對(duì)象、函數(shù)內(nèi)部for循環(huán)的使用以及if判斷語(yǔ)句中的條件的書寫
????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");
????????????????????}
????????????????}
????????????}
????????}
????}	?				
??????//請(qǐng)補(bǔ)充此處代碼，給正確的menu下的a元素class賦值current
</script>
</head>
</html>