1. 对象.style.样式名
弊端就是只能获取行内样式
2.window.getComputedStyle(对象，null);
最好用第二种方式
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<style type="text/css">
#box{
40px;
height: 40px;
background-color: red;
}
</style>
<body>
<button id="btn" >切换</button>
<div id="box" style="border: 1px solid #0f0;"></div>
</body>
<script>
var box = document.getElementById("box");
var btn = document.getElementById("btn");
var sty = getComputedStyle(box,null);
btn.onclick = function(){
console.log(box.style.background);
if(sty.backgroundColor == "rgb(255, 0, 0)"){
box.style.backgroundColor = "blue";
}else{
box.style.backgroundColor = "red";
}
}
</script>
</html>