javascript - 将一个标签的鼠标移入移出事件改用函数调用的方式写失败了，请热心的朋友帮我看看，非常感谢-PHP中文网问答

失败的代码在注释中
<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>淘宝卖家中心</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        li {
            list-style: none;
        }
        a {
            text-decoration: none;
            color: #000;
        }
        .nav-option {
            width: 110px;
            height: 30px;
            line-height: 30px;
            overflow: hidden;
            margin: 50px auto;
        }
        .nav-option .sell-center:hover{
            color: orange;
        }
        .nav-option ul li {
            line-height: 28px;
        }
        .show {
            overflow: visible;
        }
        .bgcGray {
            background-color: #F5F5F5;
        }
        .bgcWhite {
            background-color: #fff;
        }
    </style>
    <script>
        window.onload = function () {
            var navOption = document.getElementById("nav-option");
            var arrLi = navOption.getElementsByTagName("li");
            var len = arrLi.length;

            navOption.onmouseover = function () {
                navOption.className += " show";
            }
            navOption.onmouseout = function () {
                navOption.className = "nav-option";
            }

//            想将上面两段代码，navOption的鼠标移入、移出事件改用函数调用的方式写
//             但实现不了，请问哪里错了？
//            fnTab(navOption,onmouseover,"nav-option show");
//            fnTab(navOption,onmouseout,"nav-option");
//            function fnTab(name,evt,cclassName){
//                name[evt] = function (){
//                    name.className = cclassName;
//                }
//            }

            for(var i=0;i<len;i++){
                arrLi[i].onmouseover = function () {
                    this.className = "bgcGray";
                }
                arrLi[i].onmouseout = function () {
                    this.className = "bgcWhite";
                }
            }
        }
    </script>
</head>
<body>
    <ul>
        <li class="nav-option" id="nav-option">
            <a href="#" class="sell-center">卖家中心</a>
            <ul>
                <li><a href="#">免费开店</a></li>
                <li><a href="#">已卖出的宝贝</a></li>
                <li><a href="#">出售中的宝贝</a></li>
                <li><a href="#">卖家服务市场</a></li>
                <li><a href="#">卖家培训中心</a></li>
            </ul>
        </li>
    </ul>
</body>
</html>