获取元素计算后的css样式封装：
function getCss(obj,attribute) { if(obj.currentStyle) { return obj.currentStyle[attribute];}else { return window.getComputedStyle(obj,null)[attribute];} }
案例：
<!DOCTYLE html>
<html>
<head>
<meta charset="uft-8" />
<style>
#box {width:100px; height: 100px; background:#dfd; position:absolute; left:100px; top:100px;}
</style>
</head>
<body>
<button >200</button>
<button >600</button>
<div ></div>
</body>
</html>
<script>
function getCss(obj,attribute) {
if(obj.currentStyle) {
return obj.currentStyle[attribute];}else {
return window.getComputedStyle(obj,null)[attribute];}
}
console.log(getCss(box,'zIndex'));
</script>