js实现选项卡代码

<div class="container">

        <ul id="box">

            <a href="#javascript">

                <li class="show">

                    <img src="https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1487161953058&di=fc5f3f927a478b1a63f6316924bf7667&imgtype=0&src=http%3A%2F%2Fwww.wallcoo.com%2Fanimal%2FMX069_Pretty_Puppies_puppy_garden_adventure%2Fwallpapers%2F1280x1024%2FGarden_adventure_of_the_little_puppy_photos_pictures_puppy_MIL56003.jpg" alt="">

                </li>

            </a>

            <a href="#javascript">

                <li>

                    <img src="http://www.wallcoo.com/animal/Pet-Miniature-Schnauzer/wallpapers/1280x1024/Miniature-Schnauzer-puppy-photo-83448_wallcoo.com.jpg" alt="">

                </li>

            </a>

            <a href="#javascript">

                <li>

                    <img src="http://tupian.enterdesk.com/2012/0831/zyz/04/1345599339UDIPTP.jpg" alt="">

                </li>

            </a>

        </ul>

        <div class="btn" id="btn">

            

            <span class="active"></span><i></i>

            <span ></span><i></i>

            <span ></span><i></i>

        </div>

    </div>

	*{
			margin: 0;
			padding: 0;
		}

		.container{

			width: 600px;
			height: 400px;
			border: 1px solid #b6b6b6;
			margin: 100px auto;
			position: relative;
		}
		
		.container ul li {

			list-style-type: none;
			width:600px;
			height: 400px;
			transition:1s;
			position: absolute;
			left: 0;
			top: 0;
			opacity: 0;
		}

		.container ul li.show{

			opacity: 1;
		}
		
		.container ul li img{
			
			width: 100%;
			height: 100%;	

		}

		.btn{

			position: absolute;
			z-index: 100;
			width: 600px;
			height: 30px;
			display: flex;
			bottom: 5%;
			justify-content:center;
		}

		.btn span{
			
			width: 30px;
			height: 30px;
			display: block;
			border-radius: 50%;
			background: #f99;
			opacity: 0.8;

		}
		.btn i {
			width: 20px;
			height: 20px;
		}

		.btn span.active{

			background: red;

		}
	

　　

var oBtn=document.getElementsByTagName('span');

var oli=document.getElementsByTagName('li')

console.log(oBtn.length)

for(var i=0;i<oBtn.length;i++){

 

oBtn[i].index=i;

oBtn[i].onmouseover=function(){

 

for(var i=0;i<oBtn.length;i++){

oBtn[i].className="";

oli[i].className=""

}

this.className="active";

oli[this.index].className="show"

}

}