obj.style.attr和obj.style[attr]有什么区别吗？为什么我用后者有效果，前者没效果？
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<style>
*{
margin:0;
padding:0;
}
div{
width:200px;
height: 80px;
background: red;
margin-bottom: 20px;
border: 4px solid black;
opacity: 0.3;
filter: alpha(opacity:30);
}
</style>
<script>
window.onload=function(){
var Li = document.getElementsByTagName("div")[0];
Li.onmouseover = function(){
startMove(this,'opacity',100)
};
Li.onmouseout = function() {
startMove(this, 'opacity', 30);
};
var timer = null;
function startMove(obj,attr,target){
clearInterval(timer);
timer = setInterval(function(){
var icur = 0;
if(attr == 'opacity'){
icur = parseFloat(getStyle(obj,attr))*100;
}else{
icur = parseInt(getStyle(obj,attr));
}
var speed = (target - icur)/8;
speed = speed > 0 ? Math.ceil(speed) : Math.floor(speed);
if(icur == target){
clearInterval(timer);
}
else{
if(attr == 'opacity'){
obj.style.filter = 'alpha(opacity:'+ (icur + speed)+')';
obj.style.opacity = (icur + speed)/100 ;
}else {
obj.style[attr] = icur + speed + "px";
}
}
},30)
}
function getStyle(obj,attr){
if(obj.currentStyle){
return obj.currentStyle[attr];
}else{
return getComputedStyle(obj,false)[attr];
}
}
}
</script>
</head>
<body>
<div></div>
</body>
</html>
