任务描述：
当鼠标移入“透明度”矩形时，该矩形透明度逐渐增加至不透明，移出该矩形，透明度逐渐恢复至初始值;同时该运动框架可以支持其它属性的变化。
示例图
<!DOCTYPE html>
<html>
<head lang="zh-CN">
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=no">
<title>任意值运动框架</title>
<style>
div {
200px;
height: 200px;
margin: 20px;
float: left;
background: yellow;
border: 10px solid black;
filter: opacity(alpha=30);
opacity: 0.3;
}
</style>
</head>
<body>
<div id='div1'>变透明度</div>
<input type='text' id='input' />
<script type="text/javascript">
//补充代码
</script>
</body>
</html>
参考代码：
oDiv1 = document.getElementById('div1');
oInput = document.getElementById('input');
oDiv1.onmouseover = function () {
startMove(this, 'opacity', 100)
}
oDiv1.onmouseout = function () {
startMove(this, 'opacity', 30)
}
function getStyle(obj, name) {
if (obj.currentStyle) {
return obj.currentStyle[name];
}
else {
return getComputedStyle(obj, null)[name];
}
}
function startMove(obj, attr, iTarget) {
clearInterval(obj.timer);
obj.timer = setInterval(function () {
var cur = 0;
if (attr == 'opacity') {
//Math.round()四舍五入取整主要是针对低浮点数的精度问题。
cur = Math.round(parseFloat(getStyle(obj, attr)) * 100);
} else {
cur = parseInt(getStyle(obj, attr));
}
var speed = (iTarget - cur) / 6;
speed = speed > 0 ? Math.ceil(speed) : Math.floor(speed);
if (cur == iTarget) {
clearInterval(obj.timer);
} else {
if (attr == 'opacity') {
obj.style.opacity = (cur + speed) / 100;
obj.style.filter = 'alpha(opacity=' + (cur + speed) + ")";
oInput.value = obj.style.opacity;
}
else {
obj.style[attr] = cur + speed + 'px';
}
}
}, 30)
}