js中利用立即执行函数实现京东大小图切换

<ul>
<li><img src="../../../img/练习/s1.jpg" alt=""></li>
<li><img src="../../../img/练习/s2.jpg" alt=""></li>
<li><img src="../../../img/练习/s3.jpg" alt=""></li>
</ul>
<script>
var img=document.getElementById('show_img');
var lis=document.getElementsByTagName('li');

for (var i=0;i<lis.length;i++){
!function (index) {
lis[index].onmouseover=function () {
img.src='../../../img/练习/b'+(index+1)+'.jpg';
}
}(i);
}
</script>