为何用js 改 style.listStyleType 不生效？

No problem!
L@_@K
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title> new document </title>
    <meta name="generator" content="editplus" />
    <meta name="author" content="Gao YiXiang" />
    <meta name="email" content="[email protected]" />
    <meta name="keywords" content="javascript dhtml dom" />
    <meta name="description" content="I love web development." />
</head>
<body>
    <ul onmouseover="this.style.listStyleType='circle'" 
    onmouseout="this.style.listStyleType='square'">
        <li>123</li>
        <li>456</li>
    </ul>
</body>
</html>