編程練習(xí)
運(yùn)用javascript知識(shí)，實(shí)現(xiàn)根據(jù)class name獲取對(duì)象并返回、給頁面元素增加class等功能函數(shù)，并實(shí)現(xiàn)在滾動(dòng)時(shí)根據(jù)滾動(dòng)條的位置自動(dòng)設(shè)置導(dǎo)航菜單的焦點(diǎn)。
溫馨提示 : 完成任務(wù)后，請(qǐng)驗(yàn)證是否與實(shí)踐描述效果一致，如一致，恭喜您，你已經(jīng)掌握此技能，否則，請(qǐng)重復(fù)學(xué)習(xí)此節(jié)內(nèi)容。
任務(wù)
1.定義getByClassName函數(shù)，讓函數(shù)實(shí)現(xiàn)根據(jù)class name獲取對(duì)象并返回
提示：先獲取obj中的所有標(biāo)簽，賦值給elements，然后遍歷elements，找到className相符的元素存入數(shù)組result，最后返回result
2.定義addClass函數(shù)，讓函數(shù)實(shí)現(xiàn)給對(duì)象增加class
提示：首先要判斷是否已經(jīng)有名為cls的class，如果沒有，添加即可
3.補(bǔ)充代碼，給正確的menu下的a元素class賦值current
提示：此處要遍歷menus，對(duì)menus中的每一個(gè)元素判斷href屬性值和currentId是否相符，并根據(jù)判斷結(jié)果決定是移除名為current的class，還是增加名為current的class。
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
<title>地狗購物網(wǎng)——網(wǎng)頁定位導(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>
//定義getByClassName函數(shù)，讓函數(shù)實(shí)現(xiàn)根據(jù)class name獲取對(duì)象并返回
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, "");
}
}
//定義getByClassName函數(shù)，讓函數(shù)實(shí)現(xiàn)給對(duì)象增加class
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;
}
}
//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>
<body>
<div id="menu">
<ul>
<!--運(yùn)用錨點(diǎn)，實(shí)現(xiàn)導(dǎo)航定位。-->
<li><a href="#" class="current">1F 男裝</a></li>
<li><a href="#">2F 女裝</a></li>
<li><a href="#">3F 美妝</a></li>
<li><a href="#">4F 數(shù)碼</a></li>
<li><a href="#">5F 母嬰</a></li>
</ul>
</div>
<div id="content">
<h1>地狗購物網(wǎng)</h1>
<div id="item1" class="item">
<h2>1F 男裝</h2>
<ul>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//53660fce0001111903990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//53660fce0001111903990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//53660fce0001111903990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//53660fce0001111903990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//53660fce0001111903990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//53660fce0001111903990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//53660fce0001111903990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//53660fce0001111903990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//53660fce0001111903990422.jpg" alt=""/></a></li>
</ul>
</div>
<div id="item2" class="item">
<h2>2F 女裝</h2>
<ul>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//5366104c0001e5c403990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//5366104c0001e5c403990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//5366104c0001e5c403990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//5366104c0001e5c403990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//5366104c0001e5c403990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//5366104c0001e5c403990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//5366104c0001e5c403990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//5366104c0001e5c403990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//5366104c0001e5c403990422.jpg" alt=""/></a></li>
</ul>
</div>
<div id="item3" class="item">
<h2>3F 美妝</h2>
<ul>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610820001cf5b03990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610820001cf5b03990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610820001cf5b03990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610820001cf5b03990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610820001cf5b03990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610820001cf5b03990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610820001cf5b03990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610820001cf5b03990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610820001cf5b03990422.jpg" alt=""/></a></li>
</ul>
</div>
<div id="item4" class="item">
<h2>4F 數(shù)碼</h2>
<ul>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610ac00012df703990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610ac00012df703990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610ac00012df703990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610ac00012df703990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610ac00012df703990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610ac00012df703990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610ac00012df703990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610ac00012df703990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610ac00012df703990422.jpg" alt=""/></a></li>
</ul>
</div>
<div id="item5" class="item">
<h2>5F 母嬰</h2>
<ul>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610cd0001f34603990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610cd0001f34603990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610cd0001f34603990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610cd0001f34603990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610cd0001f34603990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610cd0001f34603990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610cd0001f34603990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610cd0001f34603990422.jpg" alt=""/></a></li>
<li><a href="#"><img src="http://img1.sycdn.imooc.com//536610cd0001f34603990422.jpg" alt=""/></a></li>
</ul>
</div>
</div>
</body>
</html>
請(qǐng)驗(yàn)證，完成請(qǐng)求
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