offsetWidth前添加负号有什么意义呢？我去掉这个负号时我的代码就出错
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>Document</title>
<style type="text/css">
body,img,a,div,ul,li{margin: 0px;padding: 0px;}
#div1{
width: 600px;
height: 100px;
background: red;
position: relative;
overflow: hidden;
margin:0px auto;
margin-top: 100px;
}
#div1 ul{
position: absolute;
left: 0;
top: 0;
}
#div1 ul li{
list-style: none;
float: left;
width: 150px;
height: 100px;
}
#div1 ul li img{
width: 150px;
height: 100px;
}
a{
display:block;
width: 50px;
height: 50px;
background: orange;
float: left;
margin:;
}
</style>
<script type="text/javascript">
window.onload=function(){
var oDiv=document.getElementById('div1');
var oUl=document.getElementById('ul1');
var ali=document.getElementsByTagName('li');
oUl.innerHTML+=oUl.innerHTML;
oUl.style.width=ali[0].offsetWidth*ali.length+'px';
var time=null;
var speed=2;
function move(){
if(oUl.offsetLeft<-oUl.offsetWidth/2){
oUl.style.left='0';
}
if(oUl.offsetLeft>0){
oUl.style.left=-oUl.offsetWidth/2+'px';
}
oUl.style.left=oUl.offsetLeft+speed+'px';
}
time=setInterval(move,30);
oDiv.onmousemove=function(){
clearInterval(time);
};
oDiv.onmouseout=function(){
time=setInterval(move,30);
};
document.getElementsByTagName('a')[0].onclick=function(){
speed=-2;
};
document.getElementsByTagName('a')[1].onclick=function(){
speed=2;
};
};
</script>
</head>
<body>
<div id="div1">
<ul id="ul1">
<li ><img src="img/0.jpg"></li>
<li><img src="img/1.jpg"></li>
<li><img src="img/2.jpg"></li>
<li><img src="img/3.jpg"></li>
</ul>
</div>
<a href="javascript:;">向左走</a>
<a href="javascript:;">向右走</a>
</body>
</html>
qq_小柯_12回答
-
echo_kinchao
因为是要算定位啊 -
慕男婶
因为 oUl.offsetLeft 得到的结果可能是负值。所以，在offsetWidth前面加了一个符号来比较大小。注意：offsetWidth只能是正值。因为取的是宽度嘛，宽度哪儿有负值？如果不加的话，正数是永远大于负数的
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相关分类
JavaScript