现在打开默认是向右滚动的，如果改成向左滚动。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<style>
*{
margin: 0;
padding: 0;
}
#div1{
width: 640px;
height: 120px;
margin: 100px auto;
background-color: #646464;
position: relative;
overflow: hidden;
}
#div1 ul{
position:absolute;
left:0;
top:0;
overflow: hidden;
background-color: #3b7796;
}
#div1 ul li{
float: left;
width: 160px;
height: 120px;
list-style: none;
}
</style>
<script>
window.onload = function(){
var oDiv = document.getElementById('div1');
var oUl = document.getElementById('ul1');
var speed = 2;//初始化速度
oUl.innerHTML += oUl.innerHTML;//图片内容*2-----参考图（2）
var oLi= document.getElementsByTagName('li');
oUl.style.width = oLi.length*160+'px';//设置ul的宽度使图片可以放下
var oBtn1 = document.getElementById('btn1');
var oBtn2 = document.getElementById('btn2');
function move(){
if(oUl.offsetLeft<-(oUl.offsetWidth/2)){//向左滚动，当靠左的图4移出边框时
oUl.style.left = 0;
}
if(oUl.offsetLeft > 0){//向右滚动，当靠右的图1移出边框时
oUl.style.left = -(oUl.offsetWidth/2)+'px';
}
oUl.style.left = oUl.offsetLeft + speed + 'px';
}
oBtn1.addEventListener('click',function(){
speed = -2;
},false);
oBtn2.addEventListener('click',function(){
speed = 2;
},false);
var timer = setInterval(move,30);//全局变量 ，保存返回的定时器
oDiv.addEventListener('mouseout', function () {
timer = setInterval(move,30);
},false);
oDiv.addEventListener('mousemove', function () {
clearInterval(timer);//鼠标移入清除定时器
},false);
}
</script>
</head>
<body>
<input id="btn1" type="button" value="向左">
<input id="btn2" type="button" value="向右">
<div id="div1">
<ul id="ul1">
<li><img src="img/img_1.jpg"></li>
<li><img src="img/img_2.jpg"></li>
<li><img src="img/img_3.jpg"></li>
<li><img src="img/img_4.jpg"></li>
</ul>
</div>
</body>
</html>
