没用Math.round()方法，为什么没问题
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>javascript_move</title>
<style>
*{margin: 0;padding: 0}
#box4{background-color: green;width: 200px;height: 200px;opacity: 0.3;margin: 20px;float: left;}
</style>
<script type="text/javascript">
window.onload=function(){
var movepart3=document.getElementsByTagName('div');
for(var i=0;i<movepart3.length;i++){
movepart3[i].timer=null;
movepart3[i].onmouseover=function(){
startmove3(this,100,'opacity');
}
movepart3[i].onmouseout=function(){
startmove3(this,30,'opacity');
}
}
}
function startmove3(box3,target,attr){
clearInterval(box3.timer);
box3.timer=setInterval(function(){
var a=0;
if(attr=='opacity'){
a=parseFloat(getStyle(box3,attr))*100;//这里没用Math.round();
}else{
a=parseInt(getStyle(box3,attr));
}
var speed=(target-a)/8;
speed=speed>0?Math.ceil(speed):Math.floor(speed);
if(a==target){
clearInterval(box3.timer);
}
else{
if(attr=='opacity'){
box3.style.opacity=(a+speed)/100;
console.log(box3.style.opacity);//我这里加了断点，测试opacity当前值
box3.style.filter="alpha(opacity="+(a+speed)+")";
}
else{
box3.style[attr]=a+speed+"px";
}
}
},30);
}
function getStyle(obj,attr){
if(obj.currentStyle){
return obj.currentStyle[attr];
}else{
return getComputedStyle(obj,false)[attr];
}
}
</script>
</head>
<body>
<div id="box4"></div>
<div id="box4"></div>
<div id="box4"></div>
<div id="box4"></div>
</body>
</html>没用Math.round()竟然没问题，奇了怪了，什么情况~？变量名有点奇怪，请答题的大大将就下。代码复制另存html就可以运行了。
下面是console.log()测试的opacity值：
