javascript 的 previousSibling兼容性问题

<!DOCTYPE html>
<html lang="en">
<head>
   <meta charset="UTF-8">
   <title>测试</title>
</head>
<body>
   <ul>
       <li>11</li>
       <li>22</li>
       <li id="li1">33</li>
       <li>44</li>
       <li>55</li>
   </ul>
   <script>
       window.onload=function(){
           var oLi=document.getElementById('li1');
           var prev=oLi.previousElementSibling||oLi.previousSibling;//oLi.previousElementSibling与oLi.previousSibling位置不能颠倒，颠倒之后在火狐和chrome下会出错
           prev.style.background='red';
       }
   </script>
</body>
</html>

//同理 firstChild、 lastChild、nextSibing兼容性问题解决方法一样